flood maps-an excimap work

Atlas of Flood MapsExamples from 19 European countries, USA and Japan

EXCIMAPEXEXCCIIMMAPAP

Atlas

ofFlood

Maps

Examples

from19

Europeancountries,U

SAand

Japan

Contents

1 Introduction 5

2 Flood mapping 7

3 Cartographic aspects of flood risk mapping 93.1 Layout issues and GIS approaches 9

3.1.1 Basic and explanatory information 93.1.2 Meta-data 93.1.3 Background mapping or imagery 93.1.4 Location and navigation 103.1.5 Colour palettes and symbols 103.1.6 Numerical flood data 113.1.7 Additional considerations 11

3.2 Map Content 123.2.1 Flood extent 123.2.2 Flood probability, depth, progress 123.2.3 Potential damage and casualties 133.2.4 Flood risk 133.2.5 Flood Hazard 133.2.6 Evacuation maps 13

3.3 Conclusions 13

4 Examples of flood risk maps 154.1 Austria 154.2 Belgium 25

4.2.1 Flanders 254.2.2 Wallonia 29

4.3 Croatia 334.4 Denmark 374.5 Great Britain 39

4.5.1 England & Wales 394.5.2 Scotland 53

4.6 Finland 554.7 France 594.8 Germany 67

4.8.1 Baden-Württemberg 674.8.2 Bayern (Bavaria) 704.8.3 Nieder-Sachsen / Bremen 724.8.4 Nordrhein-Westfalen 734.8.5 Rheinland-Pfalz 774.8.6 Saarland 804.8.7 Sachsen 804.8.8 Sachsen-Anhalt 83

4.9 Hungary 854.10 Ireland 894.11 Italy 934.12 Latvia 974.13 Luxembourg 994.14 Netherlands 1014.15 Norway 1094.16 Poland 113

Atlas of Flood Maps3

4.17 Spain 1194.18 Sweden 1314.19 Switzerland 135

5 Transboundary flood hazard mapping 1475.1 European Flood Risk Mapping 1475.2 Comrisk and Safecoast 1495.3 ELLA 1505.4 FLAPP 1545.5 IKRS 1555.6 SAFER 1595.7 TIMIS 159

6 Insurance maps 1636.1 CatNet 1636.2 Austria 1666.3 Czech Republic 1696.4 France 1726.5 Germany 1746.6 Italy 1756.7 USA 176

7 Evacuation maps 1797.1 Germany – Hamburg 1797.2 Japan 1807.3 Netherlands 1837.4 USA 185

7.4.1 Mississippi 1857.4.2 Florida 1867.4.3 Louisiana – New Orleans 1877.4.4 California – Sacramento 189

8 Final Remarks 195

Atlas of Flood Maps 4

Prepared for:

Atlas of Flood MapsExamples from 19 European countries, USA and Japan

November 2007

EXCIMAPEXEXCCIIMMAPAP

Contents

1 Introduction 5

2 Flood mapping 7

3 Cartographic aspects of flood risk mapping 93.1 Layout issues and GIS approaches 9

3.1.1 Basic and explanatory information 93.1.2 Meta-data 93.1.3 Background mapping or imagery 93.1.4 Location and navigation 103.1.5 Colour palettes and symbols 103.1.6 Numerical flood data 113.1.7 Additional considerations 11

3.2 Map Content 123.2.1 Flood extent 123.2.2 Flood probability, depth, progress 123.2.3 Potential damage and casualties 133.2.4 Flood risk 133.2.5 Flood Hazard 133.2.6 Evacuation maps 13

3.3 Conclusions 13

4 Examples of flood risk maps 154.1 Austria 154.2 Belgium 25

4.2.1 Flanders 254.2.2 Wallonia 29

4.3 Croatia 334.4 Denmark 374.5 Great Britain 39

4.5.1 England & Wales 394.5.2 Scotland 53

4.6 Finland 554.7 France 594.8 Germany 67

4.8.1 Baden-Württemberg 674.8.2 Bayern (Bavaria) 704.8.3 Nieder-Sachsen / Bremen 724.8.4 Nordrhein-Westfalen 734.8.5 Rheinland-Pfalz 774.8.6 Saarland 804.8.7 Sachsen 804.8.8 Sachsen-Anhalt 83

4.9 Hungary 854.10 Ireland 894.11 Italy 934.12 Latvia 974.13 Luxembourg 994.14 Netherlands 1014.15 Norway 1094.16 Poland 113


4.17 Spain 1194.18 Sweden 1314.19 Switzerland 135

5 Transboundary flood hazard mapping 1475.1 European Flood Risk Mapping 1475.2 Comrisk and Safecoast 1495.3 ELLA 1505.4 FLAPP 1545.5 IKRS 1555.6 SAFER 1595.7 TIMIS 159

6 Insurance maps 1636.1 CatNet 1636.2 Austria 1666.3 Czech Republic 1696.4 France 1726.5 Germany 1746.6 Italy 1756.7 USA 176

7 Evacuation maps 1797.1 Germany – Hamburg 1797.2 Japan 1807.3 Netherlands 1837.4 USA 185

7.4.1 Mississippi 1857.4.2 Florida 1867.4.3 Louisiana – New Orleans 1877.4.4 California – Sacramento 189

8 Final Remarks 195


1 Introduction

Aware of the growing need for flood mapping development in the future in Europe, early 2006 the EuropeanWater Directors decided to establish a European exchange circle on flood mapping (EXCIMAP).

Today EXCIMAP is an informal circle consisting of nearly 40 representatives from 24 European countries ororganizations. It has been set up for encouraging and facilitating exchanges between European experts in view ofdeveloping flood mapping. The main objective of EXCIMAP is to produce a Handbook presenting the goodpractices (available in Europe) to mobilize when executing flood mapping.

In the mean time, the European Union has adopted a European Directive on the Assessment and Management ofFlood Risks. This Directive sets out the requirement for the Member States to develop three kinds of products:• a preliminary flood risk assessment: the aim of this step is to evaluate the level of flood risk in all regions and toselect those regions on which to undertake flood mapping and flood risk management plans (see below)

• flood mapping, with a distinction between flood hazard maps and flood risk maps:− the flood hazard maps should cover the geographical areas which could be flooded according to differentscenarios. These maps are also indicated by flood extension maps;

− the flood risk maps shall show the potential adverse consequences associated with floods under thosescenarios.

• flood risk management plans: on the basis of the previous maps, the flood risk management plans shall indicatethe objectives of the flood risk management in the concerned areas, and the measures that aim to achievethese objectives. Examples are evacuation maps.

The focus in this Atlas is on river flooding, but some examples of coastal flooding are also included.

According to this directive Member states shall produce flood mapping according to some minimumrecommendations. To be consistent with this proposed European document, EXCIMAP has decided to focus itswork on the minimum requirements of the Directive concerning flood mapping.

As part of the work to be done for this Handbook an inventory was made of examples of maps and mappingprogrammes in the participating countries. The result of this inventory is this “Atlas of Flood Maps”. It containsexamples from 19 European countries, not counting the subdivisions that are made in some instances (Belgium,Great Britain and Germany) and from the USA and Japan. In addition special chapters are dedicated totransboundary flood mapping, flood maps for insurance purpose and evacuation maps.In each chapter the authors of this Atlas have made remarks on content and layout of the maps, based on generalcartographic principles.

The Atlas is compiled by the Netherlands Ministry of Transport, Public Works and Water Management. Thematerial is submitted by the EXCIMAP members. WL|Delft Hydraulics assisted to collect and organize the materialand has made both the descriptions and the analysis of the maps. After the publication of a draft edition, thematerial was reviewed by representatives of the various countries.

We hope that this valuable collection of examples will stimulate flood mapping efforts in countries that have tostart with it, and discussion to improve these practices in countries that have experiences with it already.

The editors:Jos van Alphen and Ron Passchier


2 Flood mappingFor the purpose of consistency, this Atlas is based on the same definitions as the EXCIMAP Handbook on GoodPractices on Flood Mapping:

• Flood: is a temporary covering by water of land normally not covered by water. This shall include floods fromrivers, mountain torrents, Mediterranean ephemeral water courses, and floods from the sea in coastal areas,and may exclude floods from sewerage systems

• Flood risk: is the combination of the probability of a flood event and of the potential adverse consequences tohuman health, the environment and economic activity associated with a flood event

• Flood plain maps indicate the geographical areas which could be covered by a flood (from all sources exceptsewerage systems – see above definition of flood) according to one or several probabilities: floods with a verylow probability or extreme events scenarios; floods with a medium probability (likely return period >=100y);floods with a high probability, where appropriate

• Flood hazard maps shows areas which could be flooded according to three probabilities (low, medium, high)complemented with: type of flood, the flood extent; water depths or water level where appropriate; whereappropriate, flow velocity or the relevant water flow direction

• Flood risk maps indicate potential adverse consequences associated with floods under several probabilities,expressed in terms of: the indicative number of inhabitants potentially affected; type of economic activity of thearea potentially affected; installation which might cause accidental pollution in case of flooding […] potentiallyaffected ; other information which the Member State considers useful

• Damage is the negative effect of an event or process• Residual risk is the portion of the risk remaining after the flood risk management actions have beenimplemented and taken into consideration


3 Cartographic aspects of flood risk mappingThis Chapter aims to describe the basic content and cartographic good practices of flood risk mapping. It is meantto form the background information for the description of the compilation of various examples of flood maps fromcountries that are part of EXCIMAP. The text in the first paragraph on map layout and the use of GIS is identical tothe text on cartographic aspects in the ‘Handbook of Good Practice for Flood Mapping in Europe’ produced aspart of EXCIMAP. In the second paragraph, map content is discussed.

3.1 Layout issues and GIS approachesCartographic aspects are important issues in flood mapping. They need to be adequate to the intended user tohelp ensure that the content of the maps is correctly understood and that the maps might convey the relevantinformation to their users, thus achieving the objectives for which they have been developed. This Sectiondiscusses some of the key issues related to the presentation of flood maps.

3.1.1 Basic and explanatory informationInformation that is important for use and that explain the content of the map includes:• Title: brief description of the map, including its content and / or purpose (for flood maps particularly importantare the considered probabilities or recurrence intervals

• Responsible authority (organisation responsible for the development and publishing of the maps, with contactdetails)

• Date of preparation / publication• Legend (textual description of symbols, colours, line features, etc.)• Purpose of development and intended use• Method of development• Limitations of map and / or assessment of uncertainty (if available)• Disclaimer (to enforce explanatory information and limitations, and provide legal protection to the responsibleauthority against adverse consequences of misuse)

• North and scale: preferably using scale bar as this allows for changes in page size

The scope and detail of the explanatory information should be appropriate to the intended audience.• Maps intended for public use should be simple and self-explanatory and include a clear legend, such that aslittle supporting or explanatory information as possible is required for correct interpretation.

• Maps intended for organisational users (governments, local authorities, etc.) will generally be used byprofessionals to inform decision makers that may potentially have significant impacts, and will often containmore information than public maps. They are therefore likely to require more detailed explanatory informationto help the user to fully understand the development and limitations of the maps, particularly in relation tomethods of development, limitations and uncertainty.

3.1.2 Meta-dataAppropriate meta-data should be provided where maps are issued / downloadable in GIS format. Such datashould include standard meta-data (dates, responsible organisation, etc.) as well as information necessary for useof the GIS data, including the map projection and any datum levels used. Consideration should also be given toany relevant meta-data protocols or requirements.

3.1.3 Background mapping or imageryBackground mapping (i.e., maps showing topography, towns / buildings, roads, rivers and waterbodies, land use,etc.) or imagery (often ortho-rectified aerial photographs) are almost universally provided to a flood map toprovide geographical reference for the flood information.Clear, and appropriately scaled, background mapping facilitates location directly from the principal map (althoughit might be noted that at very detailed scales this can be difficult to achieve). Care should be taken to ensure thatbackground mapping colours will not be readily confusable with those used in the flood mapping (or vice versa),and background mapping is sometimes provided in black-and-white or grey-scale to improve clarity of theoverlying flood map information.


Imagery may be more readily interpreted than mapping as a background layer, although users may find it moredifficult to geographically locate the relevant area, particularly if they are not closely familiar with the specific area.Imagery can also be expensive to procure if not already available, although Google Earth has recently become apowerful tool to provide affordable imagery (see Polish examples, Figure 4.88 and Figure 4.89).

3.1.4 Location and navigationA location plan is often provided alongside the principal flood map to help users identify the geographical locationthat the flood map represents. This plan, which may be an appropriately scaled map or schematic plan (withappropriate key locations, such as towns, roads, rivers, etc.), shows the coverage and the location of the mapwithin a wider geographical area (e.g., the nation, region or river basin).Navigation tools will be required for internet-based maps to enable users find an area of interest. Tools ofteninclude zooming (in and out) and panning and can include relocation from a location plan (as described above) ora return to default view (e.g., regional or national scale view).

An indication of orientation (direction of North bearing) and map scale are also required for correct interpretation.Scale information may be provided by:• A written scale (e.g., 1:10 000) in the title box or legend• A scale bar provided on the map; this allows easy change in paper size• Grid squares provided on the map (with the grid square size defined in legend)

3.1.5 Colour palettes and symbolsSimple flood maps may show only a single flood parameter (such as the flood extent for one flood frequency orreturn period) using a single coloured layer over a background map. The use of different colours (or shades of asingle colour) may be used to present multiple parameters (such as flood extents for multiple flood frequencies,flood depths within a given flood extent, or classes of flood hazard or risk) in a clear and comprehensible formaton a single map.The choice of colour coding may be guided by a number of factors:• Social conditioning: People are conditioned to interpret information based on colour, e.g., blue may be taken torepresent flood extents, and red, orange and green are taken to represent danger, caution and safetyrespectively. Care should be taken with respect to possible interpretations of colour, and particularlymisunderstandings.

• Graduations of colour: Graduations of colour (or within similar colours, such as red, orange and yellow orpurple, blue and green) may be used to represent different degrees of a single parameter (e.g., deeper shadesto represent more severe flooding or higher risk). The graduation may be discrete or continuous, whereby:− Discrete graduation is used to represent a set number of ranges or classes of degree (e.g., flood extents for asmall number of flood event frequencies, or specified ranges of flood depth). The choice of range or class ofdegree may be based on equal divisions, or perhaps more appropriately, on classifications related toconsequence (e.g., depth categories related to safety and the ability of people to evacuate, or to depth-damage data for economic damage calculation)

− Continuous graduation is used to represent a continuum of degree. This provides more detail but may notbe as easy to interpret as discretely graduated maps. An example of discrete and continuous graduation isshown in the next two figures.

•


Black and White Reproduction: The possible reproduction of a colour map in black-and-white might beconsidered in choosing a colour scheme, noting that different colours may appear as the same shade of greyonce copied. An example of a colour palette that does not translate well into grey scales (both the blue and redtranslate into dark grey, but the blue is low and red is high) as can be seen in the next two figures.

• Accessibility: The accessibility of maps for the partially-sighted or colour-blind should be considered in choosingcolour-schemes, particularly within the context of any national, regional or organisational regulations, policiesor guidelines.

• Clarity: Strong colours may be used to provide clarity over a coloured background map, although it might benoted that an excessive number of strong colours can make a map difficult to interpret

Hatching may be used as an alternative to different shades or colours in representing different parameters or, as ismore often the case, parameter variants. Examples might include hatching of flood extent areas that are defendedby protection measures or form flood storage areas / washlands, to differentiate these types of area from thosethat are undefended or naturally flooded respectively.The use of different line types that bound a polygon or flood extent provides another opportunity fordifferentiation. This approach is generally more suitable to visualise variants of a parameter or meta-dataassociated with the primary mapped parameters, such as differentiation between observed historic and predictiveflood extents, or an indication of uncertainty associated with a flood extent.Line types variations that might be used include ranges of line:• Thickness• Colour• Continuity (e.g., solid, chain, dashed, dotted)• Definition (e.g., clearly defined line of set thickness as opposed to fuzzy boundary)

3.1.6 Numerical flood dataFlood maps represent information graphically. This visualisation can be supplemented with numerical data, such asvalues of water level or flow, either directly as text on the map or in a table on the legend. Such data can also beprovided as attributes or tables associated with the flood maps where the maps are issued or downloadable indigital GIS format.

3.1.7 Additional considerationsIn preparing flood maps, other considerations may be relevant to the presentation.The location, type, standard and condition of flood defence assets, and other flood-related information such asevacuation routes, shelter areas, flow direction, properties, etc., can also be shown on flood maps. The scope ofthe information provided might be more or less detailed dependent on the intended purpose and audience (i.e.,public or organisational). This information may be associated with the flood maps, and possibly with particularflood cells, where the maps are provided in digital GIS format.The presentation of flood maps in trans-national or trans-regional river basins should, as far as reasonably possiblewithin the requirements and constraints prevalent in each jurisdiction, be co-ordinated and consistent inpresentation.Consistency should also exist between different types of flood maps for a given area. For example, the outerextents of flood risk zones should be spatially consistent with flood extent maps for a given flood event frequency,


and a given colour should preferably not be used to represent more than one parameter within a related set ofmaps.Most EU countries now have a multi-cultural, and hence multi-lingual, society. Minority language versions of mapsmay therefore be deemed appropriate where significant minorities exist.

3.2 Map Content

3.2.1 Flood extentThe extent of potential flooding has to be presented as surface covering the topography for a specified flood level/frequency. For reference roads, railways, houses, property boundaries and the permanent waterbodies fromwhich the floods may originate may be included. Recently Google Earth has become a powerful tool to use asbackground layer for this kind of information. A drawback of the use of Google Earth is the fact that theinteractive site depends on third-party software which, although it is rather new on the internet, might easily bediscontinued and there is always the risk that the server producing the images goes off-line for whatever reason.Other problems may occur when the layout c.q. technical aspects of Google Earth are changed.

Flood extent should be presented for a specified frequency, e.g. 1/10, 1/100 or 1/1000. In addition the protectingeffect of defence works may be shown.

3.2.2 Flood probability, depth, progressA very useful, but more advanced tool, for flood inundation mapping is the use of 2-D hydrodynamic models forthe presentation of the actual process of inundation in a simulation movie. Evidently it is not possible to capturethis type of information on a (hard-copy) map, although successive stages of the inundation process can beshown. Nevertheless this type of information is extremely valuable, especially for the assessment of most reliableescape c.q. evacuation routes. It is very important for the presentation of this information to describe precisely thespecifications that form the boundary conditions of the simulation. There are an infinite number of possibilities, interms of location of a dyke breach, initial size and development of the breach, form of the flood hydrograph thatproduces the flood (in case of river floods), local roughness conditions in the flooded area, etc.

When many computations from different locations are available (scenario simulations), the resulting informationcan be combined into probability of flooding of a gridcell and maximum inundation depth per gridcell. However,since this requires many computations, these maps are relatively scarce. These probability maps can also beproduced as flood likelihood maps for reassurance purposes.Potential (maximum) inundation depth maps exist on national, regional and local scales (1:2.500.000 – 1:10.000).In the legend it is possible to present the important relationship between inundation depth and “what to do”,depending on inundation depths of e.g.: 50 cm, 1 m, 2 m, 5 m and > 5m, (see Japan). Other related informationmay be evacuation routes, shelter areas.

3.2.3 Potential damage and casualtiesMaps about flood damage may use indicators of potential damage like:• land use (rural, urban, infrastructure, water, etc.)• real estate value /ha (shown per dike-ring, or municipality)• population density /ha (shown per dike-ring or municipality);

When more sophisticated models and information is available potential damage can be computed per gridcell as aresult of different flooding scenarios and damage functions that relate water depth to damage to structures andland use as well as to numbers of casualties. Since this is very sensitive information the data, models andassumptions have to be explained in detail in accompanying reports.

Relevant information related to this theme has to do with the objects/services that may increase flood damagesubstantially: storage of chemicals, vital networks and services (highways, railways, airport, lifeline services likeelectricity, sewerage and drinking water, hospitals, etc). This information is expressed as line or point symbols, andmay be combined with inundation-class maps.


3.2.4 Flood riskRisk is often defined as probability x adverse effects. Consequently, a flood risk map may express flood risk asexpected annual flood damage or casualties per gridcell, given the level of protection. When different floodscenarios are available, the resulting flood level frequency curve per gridcell, population density and casualtyfunction may be combined into personal risk of decease per gridcell. However, the availability of these types ofmaps is very limited, and not public. They are also difficult to interpret and it might lead to confusing informationwhen presented e.g. on the Internet.

3.2.5 Flood HazardFlood hazard maps present information on the typical dangerous aspects of floods that are important for e.g.evacuation and rescue operations: current velocity, sometimes in combination with inundation depth and/or debriscontent. This type of information may be relevant for very specific locations, e.g. near breaches in theembankment or narrow passages in river valleys, where current velocities become relevant. Therefore thisinformation is presented on detailed maps (1:2.500).

Current velocity may be presented as (magnitude) classes or vector (magnitude and direction). However, it shouldbe kept in mind that current velocity depends very much on local topography and may be of limited accuracy.Vector maps may be difficult to read when flow direction and vector locations coincide.

3.2.6 Evacuation mapsEvacuation maps present public information on “what to do”. USA has a large tradition with evacuation routes incoastal areas related to hurricane and storm surge threats, but other countries start to produce these types of mapsas well. Evacuation maps relate the magnitude of the threat (hurricane category) to areas (zipcodes!) that areevacuated or should consider it. In addition recommended evacuation routes may be shown, with detailed roadmaps about traffic contra flow direction on junctions.Complementary information may be added about things to carry with you to survive the trip (food, water,batteries, emergency telephone numbers, etc.).

In general for river flooding there are too many options for evacuation maps, as the best evacuation routedepends on the flood characteristics e.g. It is therefore suggested that such information is used as backgrounddata for decision makers instead of published information to the general public for taking decisions on evacuationroutes themselves.

3.3 ConclusionsEstablishing guidelines to the cartographic aspects of flood risk maps should be given priority, not only to avoidproblems of the public not understanding flood risk maps, but also to assure for instance that specialists dealingwith floods actually use the same basis for information, in particular where river systems are concerned that crossnational boundaries. Maps and GIS products should be tested on the public to see if they are as effective asscientists like to believe. However, it is unlikely that flood maps in the EU countries will become completelycomparable as not only the underlying methodology is different, but also the data collection and method ofmeasurement are different. It is possible, though, to arrive at a more generalized layout of the maps. This isparticularly interesting now that most countries are in the process of producing interactive Internet sites where anyuser can access the map layers.


5 Transboundary flood hazard mappingEspecially the EU-funded projects are excellent examples of transboundary flood-related projects. In Figure 5.1 anoverview is given of the flood-related EU-funded projects that were either on-going or had been recently finalizedby the time of the compilation of this Atlas. In this chapter a number of these projects will be discussed as far asthey contribute to transboundary flood mapping, but no attempt has been made to give a complete overview ofall transboundary flood mapping activities in the EU.

Figure 5.1Overview of EU-funded transboundary flood-related projects29

Another example of a transboundary approach to flood mapping is the CatNET, which aims at providing floodinformation for insurance purpose. For this reason it is further discussed, with examples, in Chapter 6.1.

5.1 European Flood Risk Mapping

European flood risk mapping is one of the components of the work carried out in the WDNH (weather-drivennatural hazards ) action by the JRC (Joint Research Centre) of the EU. Three components of flood risk have beenaddressed, i.e. flood hazard, flood vulnerability and flood exposure. The assessment is based on a database of maplayers with information on GDP, population density, land use, flood hazard, etc. The flood hazard is derived using a1 km digital elevation model and the 1 km grid European flow network developed by JRC. The outcomes from thiswork are:• Flood risk assessment for the EU + Romania and Bulgaria;• Flood risk layer: Standardised index map for flood risk (spatial resolution 1 km);• Flood risk layer: Risk assessment for NUTS3 areas.

NUTS areas (Nomenclature of Territorial Units for Statistics) are administrative divisions for all European membercountries that were introduced in 1998 and for which four different levels of detail exist. A detailed description of


29 http://www.iu-info.de/fileadmin/user_upload/news_Inhalte/Flapp_report.pdf

the development of the maps by JRC is shown in given on the website of JRC30. As an example, the flood hazardmap is reproduced in Figure 5.2. This map is based on an algorithm calculating the elevation difference of alocation with the nearest river, along the hydrological flow path. The potential flood risk is determined by thedifference in elevation and the estimated extreme water level of the nearby river. Further details on themethodology is given in the report on the website referred to earlier. In the future a higher resolution DEM will beused together with model simulations to obtain more reliable results.

In Figure 5.3 the result is shown of a combination of a land use map (Corine 2000) and the European flood hazardmap of Figure 5.2. Evidently the trend of increasing urbanisation in many parts of Europe has let to a majorincrease in flood hazard in those highly populated areas.

Figure 5.2 Flood hazard map of Europe (WDNH – JRC)


30 http://ies.jrc.cec.eu.int/fileadmin/Documentation/Reports/Land_Management/EUR_2006-2007/EUR_22116_EN.pdf

Figure 5.3 Overlay of the Corine land cover map and European flood hazard map

5.2 Comrisk and Safecoast

An example of cooperation between neighbouring countries on coastal flooding can be found in the relatedComrisk and Safecoast projects, both under the auspices of the EU.Comrisk (Common strategies to reduce the risk of storm floods in coastal lowlands) was started in 2002 and hasalready been finalized31. It was carried out by eight coastal risk management authorities from Belgium, Denmark,The Netherlands and Germany. Various studies were carried out as part of the project and the project was finalizedwith an international conference in April 2005.The Safecoast project32 forms the follow-up action to Comrisk and started in July 2005.The interesting aspects of these projects in view of this Atlas is the opportunity to bring more unity in the technicalbackground for the production of flood maps, as well as the layout of the maps themselves. The projects deal withabout 40,000 km2 of floodprone coastal area and focuses strongly on the safety of the North Sea coast taking intoaccount the expected increase of flooding danger due to climate change, with a planning horizon to the year2050. Figure 5.4 shows the floodprone area along the North Sea, covered by the Safecoast project.Also in this project, the most important aim in view of transboundary issues in flood mapping is the comparison ofdifferent flood risk assessment methods and the goal to arrive at a common ground for the planning of the coastaldefence.


31 http://comrisk.hosted-by-kfki.baw.de/32 http://www.safecoast.org/

Figure 5.4 Study area of the SAFECOAST project

A similar EU-funded project is FRAME (Flood Risk Management in Estuaries: Sustainable New Land Use in FloodControl Areas), which does have some mapping issues as well (such as a ‘Best Practice Manual’), but it isconsidered outside the scope of this Atlas. Information on the FRAME project can be found on the internet33. It ispart of a number of projects that deal with the North Sea Programme and details on related projects are found onthe internet page of this Programme34.

5.3 ELLA

The ELLA (Elbe-Labe Preventive flood management measures by transnational spatial planning) project is anotherexample of an EU-financed flood-related project which deals with transboundary issues35. One of the aims is thepreparation of flood maps with a number of examples on transboundary rivers, especially the Rhine and the Elberivers. The project is carried out with partners from Germany, Czech Republic, Austria, Poland and Hungary. Theresults of the transboundary flood mapping are available on a special internet site36, with access to maps for theRhein, Weser and Elbe (Labe) river basins, the latter being in fact the result of the ELLA project. By clicking on theRhine river, a next interactive internet site is opened37, which gives access to series of flood maps for this river(Figure 5.5). This is in fact part of the Flood Information System, which has been set up within the framework ofthe ESA project GSE RISKEOS38. Additional technological developments are being done within the project EC IPPREVIEW39. An important objective is the standardized delineation of flood hazard and flood risk maps. To theextent of their availability, the map service shows the outline and/or inundation depths of a 100 year flood and anextreme flood. Also shown are the damage potentials of at least one of these events. Additional information


33 http://www.frameproject.org/34 http://www.interregnorthsea.org/default.asp35 http://www.ella-interreg.org/36 http://www.floodmaps.de/FloodServer/37 http://www.floodmaps.de/FloodServer/go?FrameLoaderActionSprache=en38 www.risk-eos.com39 www.previewrisk.com

Figure 5.5 Interactive site for flood maps of the Rhine river basin

includes the outlined areas of recent flood events, which were derived from satellite imagery. Also available arehistorical flood maps. The service is completed by landuse data.

As an example, flood extension and damage potential maps are shown for the transboundary region along theDutch – German border in Figure 5.6 and Figure 5.7. The legend to these two maps is shown in Figure 5.8. Thetwo maps show the location where the Rhine river, after passing the Dutch border, splits into various branches. Ingreen the region is shown that would be flooded in an extreme event, with water flowing along a differentNorthern route from the Rhine in Germany directly overland towards one of the Rhine branches (“IJssel”) in theNetherlands.

Other combinations of flood map items and land use are possible, but the combination of land use map anddamage map is not easy to distinguish (too many items on the map and mixed colours not included in the legend),although this would be the most interesting combination.


Figure 5.6 Flood extension map for Rhine river along Dutch – German border


Figure 5.7 Damage potential map for Rhine river along Dutch – German border

Figure 5.8 Legend to the flood extension and damage potential map

The flood mapping of the Elbe (Labe) river of the ELLA project is a good example of a transboundary effort forGermany and the Czech Republic. However, this is less interesting as an example in this Atlas as the boundaryregion between the two countries, being a mountainous area, does not exhibit any major flood threat. It does usethe same type of layout, though, for the two countries involved as was the case for the maps of the Rhine river.This is evident from the map example shown in Figure 5.9, which shows the flood extent for an extreme flood anda flood with a return period of 1/100 year, in combination with a land use map.


Figure 5.9 Combination of flood extension and land use map for the city of Dresden (ELLA project)

5.4 FLAPP

Another interesting EU-funded project is the 'Flood Awareness & Prevention Policy in border areas' (FLAPP). Theproject started in 2005 and is now in its final stage. One aspect of the project is the production of a ‘good practicebook’, which in itself has various components. For the transboundary flood mapping issue, an importantcomponent is the production of the cross-border flood maps for the cities of Görlitz and Zgorzelec on the Nyssariver between Germany and Poland. Information on the project is provided on the internet site of FLAPP40.The Nyssa river forms the border between the towns of Görlitz and Zgorzelec, which were separated in 1945through a redrawing of the borders after the Second World War. The aim of the project was to create a commonhazard zone and flood information map on a scale of 1:5,000 in 3 languages (English/German/Polish). The mapcontains the flood plains of different events (return periods of 1/20, 1/50, 1/100, 1/200 and 1/500 years) whichhave been taken form the Saxon flood control plan for the Nyssa elaborated in 2004. Furthermore additionalinformation with regard to endangered infrastructure, municipal planning and calamity defence are displayed onthe map. In this map flood risk in a certain area is displayed via hazard zones (high, medium, low and residualrisk). These zones are determined through overlapping intensity and frequency of a flood event. The map can beused to communicate flood risk to the public and to integrate information on flood risk into spatial planning of themunicipalities. An example of part of this map is shown in Figure 5.10, showing the flood extension for the variousreturn periods. It is not clear whether the ‘Hqextrem’ refers to the 1/500 year return period. There is alsoinformation on evacuation problems on this map (indication of a bridge in red that is flooded for an event with areturn period of more than 1/200 year).


40 http://www.flapp.org/cmsEN/cms/index.asp?itemId=328

Figure 5.10 Example of a transboundary map of the Nyssa river from the FLAPP project

5.5 IKRS

Regarding transboundary flood mapping the most important product from the International Commission for theProtection of the Rhine is the Rheinatlas (2001). The maps of this Atlas are available on the internet41. The mapsthemselves are accessible through a clickable PDF file42. As an example, both a flood extension and a damagepotential map are shown for the transboundary region of the Rhine river at the Dutch – German border (Figure5.11 and Figure 5.12). The legends to the two types of maps are given in Figure 5.13 and Figure 5.14.Although these maps are similar to those produced by the Flood Information System (see Figure 5.6 and Figure5.7), the maps of the IKRS give the damage potential in quantative terms (Euro / m2), while the Flood InformationSystem gives only a relative (qualitative) scale (see legend in Figure 5.8). As such the maps of the IKRS are farmore detailed and provide the user with a better level of information.


41 http://www.rheinatlas.de/42 http://www.iksr.org/index.php?id=302&type=0#

Figure 5.11 Flooding extension map for the Rhine river at the Dutch – German border


Figure 5.12 Damage potential map for the Rhine river at the Dutch – German border


Figure 5.13 Legend of the flooding maps of IKRS

Figure 5.14 Legend of the damage maps of IKRS


5.6 SAFER

The SAFER ((Strategies and Actions for Flood Emergency Risk Management) project aims to develop innovativestrategies and prevent and mitigate fluvial and coastal flood damage by working with organisations and agenciesat different levels. The five partner regions involved in the project work are adopting a common approach inimplementing these strategies. The project is approved under the INTERREG IIIB NWE Programme and part-funded by the European Union (ERDF). A component that is related to transboundary flood mapping is theWorkpackage ‘Hazard Mapping’, which aims at producing a common methodology to produce and provide floodhazard information to all the partners. Examples of the results of this work package can be found alreadyelsewhere in this Atlas, e.g. for the German region of Baden-Württemberg (see Chapter 4.8.1), who is the leadpartner in this project. An example of a map that is drawn according to the SAFER hazard mapping methodologyis shown in Figure 4.43 for the Neckar river.

5.7 TIMIS

Transnational Internet Map Information System (TIMIS) Flood is a contribution to a uniform EU policy for floodprotection and is meant to become a model for other regions with transnational flood issues. TIMIS focuses onboth flood hazard mapping and flood forecasting for the border region of Luxembourg, Germany and France.In Figure 5.15 the extent is shown of the TIMIS project for both flood hazard mapping (approx. 22,500 km2 >90rivers and >3000 km length of river) and flood forecasting (about 55,000 km2). The project will produce by theyear 2008 transnational hazard maps on a scale of 1:25,000, showing four hazard stages and a transnational GISon flood for hazard, forecasting and warning. The maps are accessible through an interactive internet site43 (Figure5.16). An image of the future GIS environment for flood-hazard related information is shown in Figure 5.17.

Figure 5.15 Extent of the region of the TIMIS project


43 http://www.timisflood.net/en/

Figure 5.16 Internet page for the viewing of interactive flood hazard maps from the TIMIS project

Figure 5.17 Example of the GIS environment of TIMIS for accessing the flood-related information


An example of a map produced by TIMIS is shown in Figure 5.18 for a tributary of the Mosel river in Luxembourg.This is another example of the flood hazard map on a transboundary river, where the same map layout and legendis used on both sides of the border (see also Chapter 4.8.5 on Rheinland-Pfalz). The maps are produced using thefollowing information:• High-precision DTM• River cross-sections• Hydraulic modelling• Hazard classification using four hazard levels.

The four hazard levels are determined by specific combinations of intensity, velocity and frequency of the events.The legend of the hazard levels is shown in Figure 5.19.

Figure 5.18 Flood hazard map for a tributary of the Mosel river in Luxembourg


Figure 5.19 Legend of the four hazard classes used in the TIMIS project


6 Insurance maps6.1 CatNet

CatNet is an interactive map tool from the insurance company Swiss RE44. It contains information on a number ofnatural hazards, including tornados, earthquakes, ‘European winterstorm peak gust’, hail, volcanoes, etc., but alsoflood risk and is regarded as a first attempt at a Worldwide Natural Hazard Atlas45. The CatNet flood zones arebased on a wide variety of heterogeneous sources. Therefore, depending on the country, either storm surgeand/or fresh water flood zones are displayed. The main page of the interactive hazard atlas of CatNet is shown inFigure 6.1 and the selection menu in Figure 6.2. The CatNet is accessible for external users who do have toregister before they can use the information, but only for a trial period of 8 weeks, after which it is a commercialservice.

Figure 6.1 Main user graphical user interface of CatNet


44 http://www.swissre.com/45 http://www.esri.com/news/arcuser/0402/swissre.html

Figure 6.2 Selection of three bordering countries to extract information on flood hazard in CatNET

CatNet covers a number of European countries. The flood risk information is included for the following countries(with short description of their content):• BelgiumFreshwater flood zones are calculated by Swiss Re’s proprietary multiple regression approach. Zones describenaturally flooded areas affected every 100 years. The effect of flood protection measures was not taken intoaccount and flood zones along canals are not depicted.

• Czech RepublicFresh water flood zones are calculated by Swiss Re’s proprietary multiple regression approach. Zones describenaturally flooded areas affected every 50, 100, 250 and 500 years. The effect of flood protection measures wasnot taken into account and flood zones along canals are not depicted.

• GermanyFresh water flood zones for 10, 50 and 200 year water levels are available. Original data for 10 and 50 yearflood zones have been calculated by Institut für Angewandte Wasserwirtschaft und Geoinformatik (IAWG),Ottobrunn; Germany. Orginal data for 200 year flood zones have been calculated by Institut für AngewandteWasserwirtschaft, Munich, Germany.The zones for Germany are the result of hydraulic calculations carried out for a river network with a total lengthof around 50,000 kilometres. The calculations were conducted using a Digital Elevation Model (DEM) with ahorizontal resolution of 50*50 metres. They do not take flood protection measures into account, i.e. the 10 and50 year zones are rather too conservative. The flood zones depicted may vary from those in the ZÜRS software(see Chapter 6.5) provided by the German Insurance Association (GDV).There is also information available on the Elbe flood event of August 2002.

• ItalyFreshwater flood zones are calculated by Swiss Re’s proprietary multiple regression approach. Zones describenaturally flooded areas affected every 100 years.

• HungaryThe 100 year and 1000 year zones are based on the 1977 series of ‘Magyarország árvízvédelmi terképei,VITUKI, 1977’ maps at 1:100,000 scale, which were transferred by VITUKI to a digital format. Areas inundated


every 50 years were subsequently introduced by Swiss Re.• NetherlandsThe zoning reflects the design level of the 53 areas defined by the dike ring system (dijkringgebieden) in theNetherlands, as published by the ‘Meetkundige Dienst’, afd. GAT, Delft, 1996. The protection level of thediked-in areas exceeds 1000 years. Elevated areas outside the dike-in areas are classified as ‘no data’.

• SlovakiaFresh water flood zones are calculated by Swiss Re’s proprietary multiple regression approach. The zonesdescribe naturally flooded areas affected every 20, 50, 100, 250 and 500 years. The effect of flood protectionmeasures was not taken into account and flood zones along canals are not depicted.

• United KingdomThe scope of the flood zones in the UK is limited to areas affected by coastal hazards (saltwater flooding) andbased on a study by Dr. J.C. Doornkamp of the University of Nottingham in 1996.

There are also maps and data for Argentina, Israel and the USA.

If we look at the geographical coverage of the CatNET it is evident that this is another example of a transboundaryflood mapping as the combination of the Czech Rebublic, Slovakia and Hungary form one continuous region forwhich the flood maps are available. An example is shown in Figure 6.2.

Examples of flood maps available in the CatNET system are shown in Figure 6.3 for Slowakia (which shows thetransboundary coverage with Hungary south of Slovakia) and in Figure 6.4 for Germany (Sachsen-Anhalt).

In general the cartographic layout of the maps is attractive and easy to read, but the level of detail does not allowthe user to acquire a very precise level of detail in the information. The use of the colours, starting from dark bluefor low return period (1/20 yr) to grey for high return periods (500 yr and larger) is unusual and does not providethe user with an intuitive idea of increased danger level. However, in practice this grey colour represents thoseregions that are not threatened by river flooding, or at least not by any major river.

Figure 6.3 CatNet map example: flood risk mapping in Slovakia


Figure 6.4 CatNet map example: flood risk mapping in Sachsen-Anhalt (Elbe river)

6.2 Austria

HORA is an example of a successful public private partnership (PPP) on flood risk zoning and mapping in Austria.Following massive damages after heavy rainfalls and flooding in summer 2002 in Austria, insurance industry andpublic authorities in Austria under guidance of the Ministry of Agriculture (Lebensministerium) and the AustrianInsurance Association signed a PPP-contract (available in German and English) stating a common project for thedevelopment of a public, common and admission-free risk zoning tool (internet access via Lebensministerium).Common goal was to create an open risk zoning platform for flood and earthquake. Public authorities weredelivering GIS basis data, modelling and development was done by insurance and reinsurance industry. No directexchange of any sort took place, the common result is open to the public since June 1st 2006.

Local risk zoning and mapping is for several regions already available on the HORA system as well.. One canchoose the option under "Legende", if more detailed public information (than probabilistic zoning for 25000 kmriver length in HORA) is already existing and HORA has got public access to this local or regional zoning-information (e.g. for the region of Carinthia). There one can see the risk zones in different colours (yellow and redinstead of blue).

From the point of view of the insurance industry, at a later stage, HORA is expected to develop into a PML(Probable Maximum Loss)-assessment system for underwriters and risk managers. The fully working public systemwill be dedicated for individual information (and work for insurance industry as a second source of riskinformation).

The information from the HORA project is available on the internet46. An impression of the interactive internet siteis shown in Figure 6.5. After starting up the map server for the HORA site, a disclaimer is shown in red font withthe text (in German): “I have read the copyright statements and accept them as legal disclaimer”. This statementneed to be accepted by the user before the maps can be accessed. The maps give a delineation of flooding areason river catchment level for about 25.000 km of river length on scales varying from 1:10.000 to 1:50.000. Thereturn periods shown on these maps are 1/30 yr (zone 1), 1/100 yr (zone 2) and 1/200 yr (zone 3). Theinformation is not yet available for the entire country.


46 http://geoinfo.lfrz.at/website/egisroot/services/ehora2/viewer.htm

Figure 6.5 Interactive Internet site for the flood hazard map of the HORA project in Austria

Figure 6.6 HORA window for location of airport of Innsbruck with legend

Users can enter their address information and find out the potential flood risk of their property. Examples of themaps are shown in Figure 6.7 (with topographic map) and Figure 6.8 (with satellite image) for the area of theairport of Innsbruck.


Figure 6.7 Example of flood extension map for airport of Innsbruck (with topographic map background)

Figure 6.8 Example of flood extension map for airport of Innsbruck (with satellite image background)


6.3 Czech Republic

In the Czech Republic an exceptionally well-developed tool has been made available which allows the user toassess the flood risk at any location in the country using a map-based user-interface (Figure 6.9). This system,called FRAT (Flood Risk Assessment Tool), is now used by almost all property insurances in the Czech Republic,allowing them to identify high exposed risks and more accurately price flood risks.

Figure 6.9 FRAT User Interface

The tool was developed by Swiss Re, as the leading reinsurer and developer of catastrophe models, and MMC, theleading provider of GIS (Geographic Information System) technology47. It can now price selected propertiesaccording to their flood risk exposure and can also be used as a basis for improved flood accumulation reportingand control. The tool is designed as a stand-alone software solution (CD-ROM) and offers two basic functionalmodes:• The user, for instance, a risk manager or insurance agent, enters data on the property location using the fulladdress (street, house number, and city). The address, or part thereof, is located and transformed intogeographic coordinates, which are used for zoning analysis.

• The system generates information on the flood risk exposure of the selected location and displays it on-screen.The tool distinguishes six different flood risk zones (zones 1 to 6, ranging from very low to very high risk), andthe historically observed maximum flood boundary. The result is also translated into the CAP (Czech InsuranceAssociation) format for designating tariff zones.

During the past few years, a Swiss Re team of hydraulic engineers, hydrologists, GIS specialists and statisticiansdeveloped statistical methodology to derive flood risk zones based on detailed digital terrain models (DTM). Theprediction success of the methodology prompted Swiss Re to apply for a patent.• FRAT 1.0 flood risk zoning is based on the best DTM available in the Czech Republic. The DTM features ahorizontal resolution of 10m, i.e. a reading is generated for every 10m of elevation.

• Due to the high impact of local factors, such as river defences or roads which are not reflected in the highresolution DTM, the high frequency flood risk (zone 6) is not derived by the statistical methodology but bydetailed processing on the part of MMC.


47 http://www.swissre.com/INTERNET/pwswpspr.nsf/alldocbyidkeylu/ULUR-5QBJKQ

Figure 6.10 Example of geo-coding at city level and at street level

An example of the outcome of FRAT, in the form of a risk map, is shown in Figure 6.11, with a distinction into four(out of maximum six) hazard zones with increasing severity of flooding.

In August 2006 the FRAT 2.0 has been released. The new version of Flood Risk Assessment Tool, which focuses onproperty insurance risk assessment is distributed on DVD ROM media and contains address database for wholeterritory of the Czech Republic. The Address database is used for address verification and for geocoding of theproperty location. The product offers extended set of detailed city plans, covering in total over 160 cities of theCzech Republic.

The FRAT system is not freely available as it is a commercial product. Swiss Re and MMC have decided to offerFRAT 1.0 CD-ROMs for a nominal fee to Czech clients of Swiss Re, the Czech Insurance Association (CAP) and toall companies within CAP. Other insurance companies with insured interests in the Czech Republic can gain accessto the application by written request to Swiss Re or MMC.


Figure 6.11 FRAT results with flood map showing hazard zones with four steps of severity

An interesting development is the application of this technology to China. Flooding is one of the major threats tolife and property in China, but to date, the insurance industry has had to depend on experience-based ratings,which have been unreliable especially for very large and infrequent events. Further information is provided on theinternet site of Swiss-RE.

Comments on the mapsAlthough the layout of the maps is clear and serves its purpose for insurance applications, the choice of the colourgreen for risk zones is not intuitive as it suggests safety where this may be misleading. It does also conflict with theuse of green for land use (wooded areas).


Description of the zones:Zone 1 – out of probable max. floodZone 2 – up to possible max. floodZone 3 – up to average 50 years floodZone 4 – up to average 20 years flood

6.4 France

In Figure 6.12 and Figure 6.13 images of typical screens of an intranet website48 are displayed developed fordissemination and use by insurance companies of public natural zoning data, by a organization dedicated tonatural risk knowledge and prevention, for the whole French insurance market.

The information is available for consultation with GPS coordinates or downloading of datasets with relevantmetadata (as available from public authorities). Further treatment of the data for more industry specific use of thepublic zoning is under development at the level of the organization and/or at the level of each company.

Depending to the existing public data on each location, the flood extension reflects either the highest historicalone or classified in terms of floods being ‘exceptional’, ‘frequent’ or ‘very frequent’ without details on actualreturn periods, if not delivered by public authorities.

So far, the indication of urbanization is provided from the relevant themes of the CORINE Landcover land use database.

Figure 6.12 Screenshot of flood extension data sets made available to insurance companies in France (large area of Avignon, mainly on the

Rhone river, indicating the urban areas affected)


48 http://www.mrn-gpsa.org/accueil.php

Figure 6.13 Screenshot of flood extension data sets made available to insurance companies in France (three flood occurrence zones displayed

for the area of Cavaillon, indicating the urban areas affected)

Information provided on these type of maps:1. Map Titles : classification of flood zones2. Type of map: "Flood hazard zoning map, to be used by French insurance market"3. Responsible authorities / sources :a) Flood extension data sets: "waterway-data by the services of the French Ministry of Ecology and Sustainabledevelopment water authorities;

b) Referential: selected themes of CORINE Landcover, with other references to be added according to specificneeds,

c) Intranet geoservice developer ; ARMINES on Kheopsd) Project manager : MRN for French insurance associations

4. Date of publication: MRN intranet geoservice in operation since mid 2006, with steady upgrade with newpublic data according to their availability

5. Scale: maps are freely scalable on the screen according to data sets scale6. Explanation of legend: according to public data sets7. Stage of program: further development for added value services in process, but depending to future theevolution of insurance scheme.


6.5 Germany

In Germany a numeric tool for classification of flood zones developed by German insurance association (GDV) isavailable (Figure 6.14) under the name ZÜRS Zonierungssystem für Überschwemmung, Hochwasser undRückstau.

Figure 6.14 Classification of flood zones update ZÜRS 2006 – area of flood hazard (Regensburg)

The following information is available on this type of maps:1. Map Title : Classification of flood zones update ZÜRS 2006 – area of flood hazard (Regensburg)2. type of map: "Flood hazard zoning map, produced and used by the insurance market in Germany"3. Responsible authorities / sources :a) waterway-data by the German water authorities;b) maps by "NAVTEQ";c) flood-zoning by "IAWG",d) programming and additional data by "ESRI", "con-terra" and "geomer";e) supervisor and project manager: "German insurance association, GDV"

4. date of publication: ZÜRS Version 2.0.12; released August 20065. scale: 1:21.151 (scale of this special map as seen on the maps footer, ZÜRS-maps are freely scalable)6. explanation of legend:a) GK 4, high hazard: flood at least once in 10 yearsb) GK 3, moderate hazard: flood at least once in 10-50 yearsc) GK 2, low hazard: flood at least once in 50-200 yearsd) GK 1, very low hazard: flood rare than once in 200 years or nevere) B, additional information: small river

7. stage of program: first release of ZÜRS in 2001, ZÜRS 2.0.12 is the fourth release since then.


49 Zonierungssystem für Überschwemmung, Rückstau und Starkregen

6.6 Italy

In Italy the insurance association (ANIA) provides flood hazard maps for insurance purposes via CEA, theEuropean insurance and reinsurance federation. The maps show the flood extension according to different returnperiods. They are produced under the responsibility of the Public Basin Authorities or ANIA itself under a special(SIGRA) project50 . The official internal release is planned for June 2007 and no public release has yet beenestablished. The maps are produced on a scale of 1:25,000 to 1:5,000 for the SIGRA project maps. In Figure 6.15an example of a screenshot of a flood hazard map is shown. In general the layout of the maps is straightforward,although the use of green is unusual as it is normally associated with safety. Nevertheless it is used here for thefloods with the lowest return period (50 years), i.e. the highest threat of inundation.

Figure 6.15 Example 1 of Regione UMBRIA/Provincia di Perugia/Comune di Torgiano

Legend of the map:Green return period = 50 yearsBlue return period = 200 yearsRed return period = 500 years


50 http://www.ania.it/sist_inf/prog/sigra/index.asp

6.7 USA

Although this Atlas is restricted to examples of flood mapping in the EU countries, as a reference the extensivemapping program in the USA is very interesting to include in this chapter on flood mapping for insurance purposessince this program started already in 1969. The program, called National Flood Insurance Program (NFIP), is aFederal program enabling property owners in participating communities to purchase insurance protection againstlosses from flooding51. This insurance is designed to provide an insurance alternative to disaster assistance to meetthe escalating costs of repairing damage to buildings and their contents caused by floods. Participation in the NFIPis based on an agreement between local communities and the Federal Government that states if a community willadopt and enforce a floodplain management ordinance to reduce future flood risks to new construction in SpecialFlood Hazard Areas (SFHA), the Federal Government will make flood insurance available within the community asa financial protection against flood losses.The program is administrated by FEMA (Federal Emergency Management Agency) which identifies flood hazardareas throughout the U.S. and it's territories by producing Flood Hazard Boundary Maps (FHBMs), Flood InsuranceRate Maps (FIRMs), and Flood Boundary & Floodway Maps (FBFMs). Several areas of flood hazards are commonlyidentified on these maps. One of these areas is the Special Flood Hazard Area (SFHA) or high risk area defined asany land that would be inundated by a flood having a 1-percent chance of occurring in any given year (alsoreferred to as the base flood). The high-risk area standard constitutes a reasonable compromise between the needfor building restrictions to minimize potential loss of life and property and the economic benefits to be derivedfrom floodplain development. Development may take place within the SFHA, provided that development complieswith local floodplain management ordinances, which must meet the minimum Federal requirements. Floodinsurance is required for insurable structures within high-risk areas to protect Federal financial investments andassistance used for acquisition and/or construction purposes within communities participating in the NFIP.

An important distinction is made between FHBMs and FIRMs. A Flood Hazard Boundary Map (FHBM) is based onapproximate data and identifies, in general, the SFHAs within a community. It is used in the NFIP's EmergencyProgram for floodplain management and insurance purposes. A Flood Insurance Rate Map (FIRM) usually is issuedfollowing a flood risk assessment conducted in connection with the community's conversion to the NFIP's RegularProgram. If a detailed assessment, termed a Flood Insurance Study (FIS), has been performed, the FIRM will showBase Flood Elevations (BFEs) and insurance risk zones in addition to floodplain boundaries. The FIRM may alsoshow a delineation of the regulatory floodway. After the effective date of the FIRM, the community's floodplainmanagement ordinance must be in compliance with appropriate Regular Program requirements. Actuarial rates,based on the risk zone designations shown on the FIRM, are then applied for newly constructed, substantiallyimproved, and substantially damaged buildings.

The FIRM is the basis for floodplain management, mitigation, and insurance activities for the National FloodInsurance Program (NFIP). Insurance applications include enforcement of the mandatory purchase requirement ofthe Flood Disaster Protection Act, which "... requires the purchase of flood insurance by property owners who arebeing assisted by Federal programs or by Federally supervised, regulated or insured agencies or institutions in theacquisition or improvement of land facilities located or to be located in identified areas having special floodhazards" (Section 2 (b) (4) of the Flood Disaster Protection Act of 1973). In addition to the identification ofSFHAs, the risk zones shown on the FIRMs are the basis for the establishment of premium rates for flood coverageoffered through the NFIP.The Standard DFIRM Database presents the flood risk information depicted on the FIRM in a digital formatsuitable for use in electronic mapping applications. The Standard DFIRM database is a subset of the EnhancedDFIRM Database that serves to archive the information collected during the flood insurance study.In the maps a number of types of areas are distinguished using a coding. The most important codes used are:

Zones AE: Areas subject to inundation by the 1-percent-annual-chance flood event determined by detailedmethods. BFEs are shown within these zones. Mandatory flood insurance purchase requirements apply.Zone AH: Areas subject to inundation by 1-percent-annual-chance shallow flooding (usually areas of ponding)where average depths are between 1 and 3 feet. BFEs derived from detailed hydraulic analyses are shown inthis zone. Mandatory flood insurance purchase requirements apply.Zone AO: Areas subject to inundation by 1-percent-annual-chance shallow flooding (usually sheet flow on


51 http://msc.fema.gov/

sloping terrain) where average depths are between 1 and 3 feet. Average flood depths derived from detailedhydraulic analyses are shown within this zone. Mandatory flood insurance purchase requirements apply.Zone A99: Areas subject to inundation by the 1-percent-annual-chance flood event, but which will ultimatelybe protected upon completion of an under-construction Federal flood protection system. These are areas ofspecial flood hazard where enough progress has been made on the construction of a protection system, such asdikes, dams, and levees, to consider it complete for insurance rating purposes. Zone A99 may only be usedwhen the flood protection system has reached specified statutory progress toward completion. No BFEs or flooddepths are shown. Mandatory flood insurance purchase requirements apply.Zone AR: Areas that result from the decertification of a previously accredited flood protection system that isdetermined to be in the process of being restored to provide base flood protection. Mandatory flood insurancepurchase requirements apply.Zones X: Areas identified in the community FIS as areas of moderate or minimal hazard from the principalsource of flood in the area. However, buildings in these zones could be flooded by severe, concentrated rainfallcoupled with inadequate local drainage systems. Flood insurance is available in participating communities but isnot required by regulation in these zones.Zone D: Unstudied areas where flood hazards are undetermined, but flooding is possible. No mandatory floodinsurance purchase requirements apply, but coverage is available in participating communities.

The flood maps can be used by a graphical user interface (Figure 6.16). In Figure 6.17 an example is given of theflood maps that are produced by FEMA as part of NFIP.

An overview of all flood information and links to maps in the USA is available on the internet52.

Figure 6.16 User-interface of the NFIP for selection of flood maps


52 http://www.floodsmart.gov/floodsmart/pages/index.jsp

Figure 6.17 Example of the FEMA – NFIP flood insurance maps (Colorado – Boulder County)


53 http://fhh.hamburg.de/stadt/Aktuell/behoerden/stadtentwicklung-umwelt/bauen-wohnen/hochwasserschutz/start.html54 http://fhh.hamburg.de/stadt/Aktuell/behoerden/inneres/katastrophenschutz/service/merkblaetter/start.html

179 Atlas of Flood Maps

7 Evacuation maps7.1 Germany – Hamburg

For the city of Hamburg, detailed information is available on the internet on the activities that are beingimplemented for the purpose of flood protection. Maps are available for several parts of the city on flood hazardand the evacuation routes. On Figure 7.1 a detailed map is shown of part of the city (Wilhelmsburg) with anindication of the evacuation zones corresponding to different water levels (6.5m and 7.5m), the location ofevacuation locations (‘Fluchtburgen’, indicated with ‘F1….8’), emergency residences (‘Notunterkünfte’, indicatedwith ‘N1…4’) and busstops (‘H’) from where evacuation busses will depart. The maps are accompanied by anextensive description of the expected situation in case of flooding and detailed advice to the general public how toact in such circumstances.

This is a good example of a well-planned information package for urban population in a very large city. Theinformation is well-presented and easily accessible, although the files themselves may prove large for slow-speedinternet connections.

Figure 7.1 Part of the map with flood protection and evacuation zones of the city of Hamburg with (German) legend

55 http://www.city.toshima.tokyo.jp/english/bousai/hazardmap/index.html56 http://www.icharm.pwri.go.jp/html/docu/jan_20_22_2004_ws/pdf_output/hiroki.pdf

180Atlas of Flood Maps

7.2 Japan

In Japan municipalities are obliged to inform their inhabitants on the flood risk conform the Flood Fighting Act,established in 2001. Since 2005 the municipalities are also obliged to take a pro-active attitude by distributingflood risk and inundation maps freely among the inhabitants in order to increase the flood-preparedness and, as asecondary goal, to contribute to the spatial planning within the municipality. The flood maps are prepared in twosteps:1. the Ministery of Land, Infrastructure and Transport and the prefecture (for resp. nationwide and regionallyadminstred river basins) determine the flood-prone areas;

2. the municipalities produce the Flood Hazard Maps.

The flood maps are produced following a nationwide standard that is determined by the Ministry, which e.g.establishes the inundation depth classes (0 – 50, 50 – 100, 100 – 200, 200 – 500 & > 500 cm) and thecorresponding colour codes. The choice of those depth classes is based on ‘human characteristics’:• 0 – 50 cm: most houses will stay dry and it is still possible to walk through the water;• 50 – 100 cm: there will be at least 50 cm of water on the ground floor and electricity will have failed by now;• 100 – 200 cm: the ground floor of the houses will be flooded and the inhabitants have either to move to thefirst floor or evacuate;

• 200 – 500 cm: both the first floor and often also the roof will be covered by water. Consequently evacuation isthe logic choice of action now. The same applies, evidently, for the depth class > 500 cm.

Similar to the situation in e.g. the Netherlands, the flood inundation maps are based on hydrodynamic calculationsfor several scenarios of possible locations of dike failure. The final map is based on the scenario that would causethe maximum number of victims, i.e. a worst case approach. The return period of the flood that is shown on themaps depends on the region as a function of potential damage.Once such maps have been made on municipal level, the municipality adds local information that is relevant forevacuation, such as the location of shelters, important buildings, evacuation routes, etc., as well as information onthe items that should be taken along during an evacuation. On some maps space is left for the user to draw apersonal evacuation route map based on the particular situation of the person or family.All the maps are distributed free of charge to the public on scales of 1:5.000 to 1:10.000, and in some cases theycan be downloaded from the internet. It is the task of the municipality to keep the maps up to date.

Examples of flood maps that are available to the public are shown in Figure 7.2 for the city of Toshima, using thedepth inundation classes mentioned above. As in most cases the legend is only given in Japanese, although insome cases an English legend is provided. Further information on the preparation of the map is given on theinternet55. On this site all relevant information is given necessary for evacuation in case of flooding, including theaddresses of the shelters.

Other examples are shown in Figure 7.3 and Figure 7.4. Especially the latter gives indications of shelters,temporary shelters (which probably have fewer resources for a long duration stay), boundaries of evacuationareas, the location of flood warning speakers and, contrary to general custom, an indication of roads that shouldNOT be used for evacuation. The map also provides expected flood depths, although no indication is given towhich return period this applies, and the limits of a recent historical flood. Although this map has some interestingfeatures that are hardly ever found in other evacuation-type maps (like the earlier mentioned location of ‘floodwarning speakers’), the topographical layout on the scale presented is not sufficiently clear to be used in practicalsituations. It may be used, though, for preparation purposes as a training for flood situations. Further informationcan be found on the internet56.


Figure 7.2 Part of flood depth map for the city of Toshima in Japan


Figure 7.3 Evacuation map for the Japanese city of Sukagawa

Figure 7.4 Example of a flood hazard map with indications of evacuation roads


7.3 Netherlands

An example of an evacuation map in the Netherlands is shown in Figure 7.5 for polders along the Rhine river nearGermany. This maps shows clearly the mandatory evacuation routes, including indication of one-way convertedroads, closed entrances and exits, and are a easy to interpret by the general public.

In Figure 7.6 the simulation of the expected flood extension for the region of “Land van Maas en Waal” (see alsoChapter 4.14) is translated into a decision-support map that shows the areas that will either remain dry, reach awater level that leaves the first flood of dwellings dry and those areas that will reach such water depths thatevacuation will be required. In order to take decisions on the best evacuation routes, a map is produced thatshows the time of arrival of the inundation front with a depth of 50 cm at the various types of infrastructure(especially roads, see Figure 7.7). Depending on the decision up till which depth roads or other escape routes arestill safe to use, maps with the arrival time of dfferent inundation depths can be produced.

Figure 7.5 Example of an evacuation map for the Netherlands with indication of obstructions and lane direction and closed entrances and

exits

Figure 7.6 Basis for decision making on evacuation (expected inundation depth)

Figure 7.7 Time of arrival of the inundation front of 50 cm depth at infrastructure (roads/elevated areas)



57 http://www.ibiblio.org/rcip/evacuationroutes.html#sbs58 http://www.gomdot.com/cetrp/hurricane_evac_routes.pdf59 http://www.gomdot.com/cetrp/hurricane_evac_routes.pdf

7.4 USA

7.4.1 MississippiSimilar to the comments made on insurance maps, there are a number of very interesting examples of evacuationmaps that can be used as examples for the development of evacuation maps in Europe. In the USA the evacuationroutes are published both by state and central on a clickable map of the entire country57.In the maps from the USA reference is often made to the ‘contraflow’ principle, i.e. the reversing of the normaltraffic flow direction to change an ordinary two-direction road into a one-direction (evacuation) road to increaseits capacity. Special maps are prepared for such occasions that are referred to as ‘contraflow maps’. An example isgiven in Figure 7.8 for a part of the State of Mississippi58 and a detailed map of a road crossing prepared by theMississippi Department of Transport is shown in Figure 7.959.

Figure 7.8 Hurricane evacuation routes in Mississippi state with indication of ‘contraflow’ roads

Figure 7.9 Example of detailed maps prepared for road crossings in case of ‘contraflow’ situations

7.4.2 FloridaThe State of Florida produces a number of very clear and attractive evacuation maps. An example is shown inFigure 7.10. This evacuation map is accompanied by a text with an indication of the ‘best’ evacuation route foreach of the villages in the region. The colours refer to expected hurricane / storm surge force (category 1 – 5)

Figure 7.10 Evacuation map for a part of Florida60


60 http://www.firstcoastnews.com/weather/stormtrack/evacuation_map.aspx


61 http://www.dotd.state.la.us/maps/

7.4.3 Louisiana – New OrleansEvidently after the impact of the hurricane Katrina, New Orleans has become a focus of attention in terms of floodprevention. Detailed evacuation maps are available for the all of the state of Louisiana (see e.g. Figure 7.11)61,with for each road crossing a special map that indicates the contraflow plan and detailed instructions for theevacuation by car (Figure 7.12).

Figure 7.11 Part of an evacuation map for Southwest Louisiana

Figure 7.12 Detail of contraflow at a road crossing (reference to map on Figure 7.11) and detailed instructions

Another example of an evacuation map for the city of New Orleans, including a phased evacuation plan, is givenin Figure 7.13. Very detailed instructions are available in case of a hurricane threat, with emergency shelterinformation points, agency contact information, radio frequencies, a guide on how to make a ‘familycommunication plan’ and even a chapter on ‘preparing your pets’.

Figure 7.13 Part of evacuation map of area of New Orleans with phased evacuation plan



62 http://www.msa.saccounty.net/waterresources/floodready/?page=maps63 http://www.nj.gov/njoem/plan/evacuation-routes.html64 http://www.dot.state.sc.us/getting/evacuation.shtml

7.4.4 California – SacramentoA very interesting example of a combination of a flood depth map and a combined rescue / evacuation map isavailable for the County of Sacramento in California, including the city of Sacramento itself. Various detailed mapsshowing hypothetical levee breaks, inundation levels and the time it would take for waters to rise in affectedneighbourhoods, and rescue and evacuation zones have been made available on the internet62. For a specificfailure location two types of maps can be downloaded:• Flood Depth Maps: show where the water would flow over time and how deep it would get given thehypothetical flooding scenario.

• Rescue and Evacuation Route Maps: show rescue areas, evacuation areas, and potential evacuation routes.− Rescue areas, in red, indicate places where water has the potential to reach a depth of at least one foot aftertwo hours from the time of a levee failure. People would not be able to drive out and likely would bestranded and require rescue.

− Evacuation areas, in yellow, indicate places, depending on where the levee breech occurs, that could fill from1 to 26 feet of water within 10 days, giving most people time to get out safely. Flood depth details arespecified on each map.

− This map also portrays potential evacuation routes (in green) and which evacuation routes would becomeinundated over time.

A total of 18 sets of maps are available. Examples of both types of maps, with the corresponding legends, for theAmerican – River Arden region, are shown in Figure 7.14 and Figure 7.15.

Detailed maps are also available for some of the other States in the USA, especially New Jersey63 and SouthCaroline64, but provide no extra information compared to the maps already shown in this Chapter.

Figure 7.14 Flood depth map of the county of Sacramento, with indication of location of hypothetical levee failure

and inundation process in time

Figure 7.15 Rescue and evacuation route map of the county of Sacramento, with indication of location of

hypothetical levee failure and passable routes in time


8 Final RemarksIn the present document a large number of examples of floods maps are shown, produced by various Europeancountries. The aim of this document is to provide the reader with illustrative examples of various types of floodmaps that might form an inspiration for future mapping efforts. As a kind of final remarks, in this section somedo’s and don’ts are formulated regarding the flood information that can be presented in these type of maps.In some occasions map examples are described as being very clear and/of as an example of an excellent floodmap. Evidently these are the subjective opinions of the compilers of this document and the users are invited tobrowse through it and form a personal opinion that may be brought forward within the context of EXCIMAP.

Although in Chapter 1 a number of different types of flood maps are mentioned, not all these types are equallywell presented.Most countries have flood extent maps. This flood extent should be related to a specified flood frequency.Frequencies used in the maps vary from 1/30 to 1/10.000. Most countries use only 2 or 3 different frequencies(e.g. 1/100 and 1/1000, or the less accurate “frequent” and “exceptional”), Flanders seventeen (2, 5, 10, 15, 20,25, 30, 40, 50, 75, 100, 150, 200, 250, 300, 500 and 1000 years). England & Wales distinguish between floodsoriginating from the sea (1/200) and flood from rivers (1/100), while Ireland gives an indication of the uncertaintyof the flood extent. Maps become difficult to read when flood extent is presented in iso-lines (instead of colouredsurfaces) or when current velocities are presented is arrows (that may merge together with parallel current lines).

Often flood extent for different frequencies is presented in one map. Increasing intensities of blue, suggestingincreasing flood depth, represent the most frequent flooded (deeper) areas (like England & Wales, Finland,Germany). Flood depth maps may be presented for one representative flood frequency, e.g. 1/100. An interestingexample is from Japan, in which the flood depth intervals are such that it contains “danger/how to act”information for individuals. In France maps exist that also present flood duration.Information on historic floods is shown on maps from France, Finland and Ireland. With this type of informationone should be aware that since this flood event floodwave characteristics and floodplain topography may havechanged considerably and that therefore this historic flood may not representative for present conditions.However, this information is valuable to increase flood awareness.

Flood hazard maps, indicating where the combination of current velocity and waterdepth may be dangerous, arepublished in England& Wales. Austria uses the more or less comparable dragforce parameter. In Rheinland-Pfalz(Germany) and Switzerland this velocity-depth information is related to frequency, expressing this hazardinformation in a more sophisticated way for professional users. The dominant colours for this type of hazardinformation are red, orange and yellow.

In terms of flood risk maps, official maps indicating potential damage are rare. The only examples are fromGermany (Rheinland-Pfalz, Sachsen). Italy, Spain and Switzerland have official risk zone maps. These maps arebased on the probability of flooding in combination with the land use sensitivity /vulnerability to flooding. In Italyand Switzerland this risk zonation relates to spatial planning regulations and construction requirements. Specificvulnerability maps are available in England & Wales (social vulnerability of the population) and Sachsen (Germany)(vulnerable services, like hospitals).

A special group of flood maps comprise the insurance maps, which are used as a basis for both the general user, tocheck on the liability of his/her property to flooding, and the insurance companies to assess the actual risk offlooding. These maps contain information on flood risk, represented as flood extent probability on damagepotential.

Evacuation maps are slowly becoming more usual, although most of them are still produced outside the EU. USAand Japan have a large tradition on this and may be valuable when European countries start to prepare thesemaps. Examples are found in Germany and also the Netherlands. These maps concentrate on how to act when aflooding threat becomes evident (evacuation routes, location of refuge/shelters, etc.), often combined with

recommendations on what to take with you. Sometimes those maps are combined with “threat” information(potential flooding depth / flood extent depending on hurricane force).

Apart form flood information (the core of the map of course) some additional information is essential for a properuse of the map: adequate title, date of publishing, responsible authority, orientation of the map, scale (preferablywith a scale rod, to avoid confusion when printing or copying maps on other scales), relevant topographicinformation (roads, railways, buildings, cadastral information (e.g. in Austria)). Interesting opportunities arise whencombining flood maps with Google Earth, however care should be taken to avoid an overload of topographicinformation in this way.Other desirable information is a small set-in map to locate the mapped area. Some Finnish maps indicate the areacovered by the model calculation. In addition the map from Finland has a nice example of a Disclaimer.

Another issue is language: in some instances English is used instead of the local language, but it is recognized thatthe use of English, especially on the publicly accessible internet sites, may limit the access to the information forthose people with limited knowledge of English and the local language is preferred. The use of two languages maymake the legend too large or difficult to read. An option is evidently to provide a translation of the map labels inEnglish, especially on the internet sites.

With maps presented digitally on a computer care should be taken that the legend remains readable, especiallywith (scanned) files of original hardcopies. Still many maps will be printed as well (A3 as most frequent maximumsize), which requires that map and legend are printed on the same page.

The Atlas shows for some of the maps a wide variety of layouts. When accompanied by a clear legend this maynot be a problem, however for transboundary catchments / maps it is advisable that a certain level of uniformity isaccomplished. Nice examples of such an approach are shown in the Chapter 5 on transboundary flood mapping.

Apart from the large number of different types of layout, that will be evident when browsing through thisdocument, it is important to realize that the differences in layout are only the outside of the discrepancies betweenthe various maps that according to their titles might assume to show the same information (e.g. flood extensionfor a certain return period). More important than the differences in layout are the different methodologies that areused for the production of the flood maps. Although the return period used is the same, the actual calculationmethod may be very different and is often not apparent from the map. However, even in cases where backgrounddocuments do explain the technical details of the calculations, there are too many differences in the approachesfollowed by the various agencies that the maps would possibly become comparable or, at border locations wherethey present a continuous line of information, show the same results. And although in theory it would be possibleto use one and the same methodology, it is unlikely that the same results would be generated for e.g. borderstations as the underlying data are often contrasting and/or the length of the measurement series are different forstations in neighbouring countries.This demand for uniform approaches not only holds for border areas, but also for maps prepared for differentpurposes within a country, e.g. national programmes, EU demonstration projects and reinsurance purposes.Because of these initiatives for one area different maps may exist, all presenting some type c.q. aspect of flood riskinformation.


Colofon

Published by Ministry of Transport, Public Works and Water Management

The Netherlands.

With the help of the EXCIMAP members:

Franz Schmid, Heinz Stiefelmayer (Austria),

Wouter Vanneuville (Belgium), Didier de Thysebaert (Belgium),

Vlatko Kadic (Croatia),

Thorsten Piontkowitz (Denmark),

John Goudie, David Murphy (England),

Mikko Sane, Mikko Selin (Finland),

Nicolas Monié, Frédérique Martini, Roland Nussbaum, Marie Renne (France),

Dieter Rieger, Juergen Krempin (Germany),

Péter Bakonyi, Sandor Toth (Hungary),

Mark Adamson (Ireland),

Valentina Vitale (Italy),

Liga Kurpniece (Latvia),

Victor Jetten (ITC),

Robert Slomp (The Netherlands),

Siri Stokseth (Norway),

Radislaw Radon, Marcin Jacewicz (Poland),

José Jiminez, Javier Lastra Fernández (Spain),

Barbro Naeslund-Landenmark (Sweden),

Roberto Loat (Switzerland).

Text: Jos van Alphen, Ron Passchier

Cover: European Environment Agency, Copenhagen, Denmark

Publishing and project management: Robert Slomp, Dick Brouwer

Lay out: Dratex, Lelystad

Print: Drukkerij Feiko Stevens

Contact: Jos van Alphen, Rijkswaterstaat, Centre for Water Management

[email protected]

EXCIMAP was organized by Frederique Martini (France) and Roberto Loat (Switzerland).

The work on this Atlas has lasted from January 2006 till October 2007 finishing with the publication of the document at

hand.

The present document contains examples of a non-exhaustive inventory of the current, existing and accessible good practices

for flood mapping in Europe. It is based on experiences and knowledge available in the countries represented in EXCIMAP.

The work of EXCIMAP started before the "Directive on the assessment and management of flood risks" endorsement (18

September 2007). The Atlas doesn’t intend to present any guidelines on how to implement the Directive despite the work

done to produce it having remained as close as possible to the Directive’s principles. Neither does the Atlas address all

requirements of the Directive.

It has not been verified if the maps and examples presented in this Atlas is compliant with the requirements of the Directive.


4 Examples of flood risk maps4.1 Austria

General informationThe flood maps of Austria are produced by the Federal Ministry for Agriculture, Forestry, Environment and WaterManagement. Two types of maps are being produced:• Flood plain maps• Flood hazard maps

Flood plain maps are provided for about 5000 km of river stretches on a scale between 1:5.000 and 1:10.000.A second group of flood plain maps are called Hochwasser Risikozonierung Austria (HORA). These maps are anexample of insurance maps and as such are further discussed in Chapter 6.2.

Flood hazard maps are produced for limited areas on scales between 1:1.000 and 1:5.000 with an accompanyingtext. They show expected flood extension for a return period of 1/100 years. For both types of maps, informationis provided on methodology, accuracy, etc. Hazard is expressed in two classes: yellow and red, which is determinedby a combination of flood depth and flow velocity (Figure 4.1).

Figure 4.1 Criteria that determine medium and high risk using depth and velocity

There are yet no flood risk or flood damage maps available.

A further distinction is made between flood control for major rives and torrents (flash floods). Flood hazard mapsfor the latter are produced for ‘catastrophic events’ with a return period of 1/150 years. Hazard zones are in factgiven for torrents, avalanches and erosion events. Maps normally cover only a certain village or community.More detailed information can be found on the internet1.


1 http://www.wassernet.at/

Comments on the mapsFour maps are shown as examples of flood maps in Austria for the same region (fictitious region ‘Muster’, Figure4.2 - Figure 4.5). As a general comment the maps are very clear and especially the cadastre background of theurbanization and infrastructure make them easy to read. It may be useful for anyone not familiar to the region tohave a small map added that shows the location within Austria. Another comment is that the North indication onthe map is rather small and may obtain a more prominent position, especially in this case where North is not at thetop of the map.

In Figure 4.2 both flood extension and expected water depth are given. In fact both water depth and water level(absolute value) are given. The latter might give an indication of the flow direction, although a flood extensionmap is normally a representation of a static situation, not of the inundation process. For the flood extension, threestandard return periods of 1/30, 1/100 and 1/300 yr are used that are the norm in Austria, but the water depth isgiven for the 1/100 yr flood event. The differences between the extensions corresponding to the three returnperiods are shown by symbols on lines instead of a system of coloured surfaces. As an alternative use can be madeof an indication of altitude similar to topographic maps, either with colours and/or putting the actual value (30 –100 – 300) within the lines.The water depths are given in an interval of 0.25 m, which is probably in line with the accuracy of the information,but the combination of colours is less common. The smallest depth (0 - 0.25 m) is shown in light blue and darkerhues of blue are used for larger depths up to 1.25 m, but then a shift is made to green with increasing depthindicated by lighter hues (up to 3.00 m). Green is normally used as an indication of safety and as was explained inChapter 3.1. Water depth is preferably indicated by hues of blue. In case there are many intervals the differencesbetween the various shades of blue may become obliterate and it might be an option to change to a larger interval(e.g. 0.5 m) instead of using a combination of colours.Although it can be deduced from the legend that the flood extension and water depth in numbers refer to theevent with a return period of 1/100 yr, this is not indicated in the subtitle of the map.

In Figure 4.3 flood hazard zones are indicated using four levels of hazard (blue, orange, yellow and red). Althoughred is normally the highest hazard, it is not immediately clear from the map what the order of the hazards is. Thecolour blue is already being used for inundation depth and may be left out of the colour palette here. It is veryuseful in this map that the hazard zones are combined with land-use information, although the overall use of thesame colour for this purpose (green) does not allow for an easy distinction between various types of landuse.There is however also another map available showing these hazard zones on top of an aerial photograph.

In the map showing flow velocities (Figure 4.4) both expected flood extension and flow velocities are shown. Theflow velocities are shown as light blue lines with the value of the velocity indicated by the length of the vector.There is no indication to which return period the velocity field belongs and the user might assume that the velocityfield is independent of the return period, which is probably not the case. Based on the extension of the velocityfield it can be deduced that it belongs to inundation with the highest (1/300 yr) return period. As a general remarkit should be mentioned that the use of vectors for flow velocities, although in general very clear, might lead toproblems in case of parallel flow lines, because the length of the vectors becomes obliterate.

An interesting and very rare type of map is shown in Figure 4.5 which gives the shear stress / drag force of theflowing water (in N/m2). There is no indication to which return period the information belongs. In general theinformation provided can be used to assess e.g. the probable locations of highest force on buildings and/or wheremajor erosion can be expected. These locations are also the most dangerous and should evidently be avoided incase of evacuation.


Figure 4.2 Flood extension and water depth map in Austria

Figure 4.3 Flood hazard map and indication of danger regions in Austria

Figure 4.4 Map showing flow velocities and flood extension for three return periods

Figure 4.5 Flood map showing drag force (shear stress - Schleppspannung) as a result of flow velocity

4.2 Belgium

4.2.1 FlandersFor the Province of Flanders in Belgium, three types of flood plain maps are developed:• The NOG-maps (Naturally flooded area map) contain the areas that are known as being flooded through soil-

mapping. These maps show the river sediments (alluvium) and slope (gravity-caused) sediments (colluvium)zones in the soilmap that has been constructed on a scale 1:20.000

• The ROG-maps (Recently flooded area map) show the recently flooded areas in the period 1988-2006 basedupon manual cartography, local terrain knowledge, photographs, (areal) movies, water authorities, Provinces,municipalities, consultants and others on topographical maps with scale 1:10.000. An automatic correction ofthe ROG-map has been performed using the DTM-Flanders (5*5 m) and GIS-techniques. This side-product iscalled the ROG-DHM map

• The MOG-maps (Modelled flooded area maps) shows the flooded areas for about 2000 km of rivers that havebeen modelled hydrological and hydrodynamical. The maps show flood extent, flood depth, flood time, floodfrequency (2, 5, 10, 15, 20, 25, 30, 40, 50, 75, 100, 150, 200, 250, 300, 500 and 1000 years). The MOG-mapcan be used till a scale of 1:2500.

The flood extension maps are available from an interactive internet site2 called the “Geo-loketOverstromingskaarten” and “Geo-loket Watertoets”; the same site is also used for other map purposes, e.g. soilmaps, colour orthophotos, satellite images, water quality, etc. The dark blue in the “Overstromingskaarten” canbe chosen for the ROG or NOG maps or for a combination of the surveyed ROG together with the MOG with areturn period of 25 years. In the “watertoets” the dark blue zones are the combination of the ROG and a MOGwith a return period of 100 years. The light blue zones are the NOG without the built-up areas. Explanation on theinteractive information, and how the flood extensions have been calculated, are given in an accompanying digitaldocument (“Risicozones overstroming – Begeleidende Nota”). Examples of a map produced with this internet siteare shown in Figure 4.8 and Figure 4.9. There is a legend to the maps, but this is written in Dutch.

Comment on the mapsOn the maps, colours are used to indicate areas that are floodable:• from any water course (pink)• from the sea (dark green)• recently flooded (ROG – dark blue)• floodable by excessive rainfall (brown)• floodable by either excessive rainfall or from a water course (orange)

Especially the two last items are rare on flood maps.

An example of a ROG maps is shown in Figure 4.6 (overview) and Figure 4.7 (example of detailed map).


2 http://geo-vlaanderen.gisvlaanderen.be/geo-vlaanderen/overstromingskaarten/

Figure 4.6 Overview of ROG areas in Flanders

Figure 4.7 Detailed ROG map in Flanders

In general the possibilities to find information on the interactive site are very good and it is easy to use also fornon-experts. A drawback is that once a certain area is selected and the user has zoomed into a detail of the map,there is no overview anymore where in Flanders the location is, e.g. there is no accompanying window that givesthe overall view of the province as is often shown on other internet sites. The amount of information is limited,but this is evidently also the reason why the maps are easy to interpret. The colour light blue for inundated area iswell-chosen, especially given the low return period. However, both the floodable areas from any water course and


‘risk zones, version 2006’ are shown in light blue and it is not immediately clear what is the difference between thetwo. Neither is there any indication in the legend on the meaning of the two different hues of blue in the map. Asimilar problem occurs in Figure 4.9 where there is no indication what is meant with the thick pink lines.

Figure 4.8 First example of a flood extension map from the Geo-loket of Flanders (Belgium)

Figure 4.9 Second example of flood extension map from Geo-Loket of Flanders (Belgium)


Also available – not on the internet – are modelled flood maps, damage maps (as a combination of hazard andvulnerability for different return periods) and risk maps as a mathematical combination of several damage maps.Some of the most important inputs are a detailed Elevation Model for the water depths and land use maps todelimit potential damage zones.

Every hydraulic scenario for the navigable waterways leads to a risk calculation with detailed maps of the presentsituation and the alternatives and a generalized overview map has to be made 2-3 times a decade.

Examples of flood risk maps are shown in Figure 4.10, Figure 4.11 and Figure 4.12.

Figure 4.10 Original flood risk map (Actual situation)

Figure 4.11 Flood risk map with alternative discharge assessment


Figure 4.12 Difference between the two foregoing maps

4.2.2 WalloniaIn view of the repeated floods in recent years and the extent of the damage they produce, the WalloonGovernment decided on 9 January 2003 to implement an overall plan for preventing and fighting against floodsand their effects on victims, called the « Plan PLUIES3 ».

One of the objectives of the “Plan PLUIES” is to determine the flooding areas for the whole territory of theWalloon Region, taking advantage of the preparatory work already done (topographic measurements of minorand major beds of rivers, inventory (survey) of areas flooded by overflowing rivers in the past, soil numericalmap,…). Concretely speaking, it consists of establishing two types of maps:− the flood hazard map, showing the territories that are likely to be flooded by overflow of rivers, which is the

main subject of this memo;− the flood risk map, showing potential damage to vulnerable, flood-sensitive elements located in zones where

there is a flood hazard.

The principles of the methodology developed by the GTI (Groupe Transversal Inondations – Cross-sector FloodGroup of the Walloon Region) were inspired by the « floodability » method developed by Cemagref, the FrenchInstitute for agricultural and environmental engineering research, duly adapted to the specificity of the Walloontopography and territory. While taking account of basic data available or being collected, it provides a coherent setof various tried-and-true scientific methods and can be applied to the entire Walloon territory. This methodologywas approved by the Walloon Government on 21 November 2002.

Flood hazard mapsA flood hazard by overflow of rivers exists in areas where flooding can take place, with variable frequency andseverity, as a result of a "natural" overflow of a river. The map shows the areas and their characteristic level ofhazard. The hazard level can have three values: low, medium and high.In practice, the degree of flood hazard is based on a combination of two factors: recurrence of flooding (returnperiod or occurrence) and its extent (depth of submersion).

• Recurrence


3 Plan PLUIES : plan de Prévention et de LUtte contre les Inondations et leurs Effets sur les Sinistrés (plan for preventing and combating floods

and their effects on the victims

Recurrence of a flood is linked to the return period of high water regimes, which implies statistical computing of ahistorical series of flow data or of a synthetic series drawn from precipitation measurements using a hydrologicalintegrated model. When the data required for statistical computing are not available, recurrence can bedetermined through evaluation of the occurrence of flooding, on the basis of observations and surveys in the field.

• SubmersionThe submersion of a flood is characterised mainly by its extent and depth. Hydraulic (2D or 1D) models thatdigitally reproduce minor and major beds of rivers are needed to determine this. When data needed to usehydraulic methods are not available, submersion is characterised by its extent, by applying the "hydropedological"method, based on information taken from digital topographic map and pedological maps, among others.

• Hazard of floodingThe flood hazard (low, medium, high) is computed from combining the values of recurrence and submersion (seeFigure 4.13). In the event of frequent flooding with a high submersion, the flood hazard will be high and,conversely, rare flooding with a low submersion will result in a low flood hazard. Note that corrective factors canbe inserted for specific conditions of the speed of the current or the duration of submersion, or when protectiveworks are present.

Figure 4.13 Determination of flood hazard in Wallonia

The combination of the methods for determining recurrence and submersion produce data which show the valueof hazard, after being integrated, cross-referenced and processed using the hazard determination grid, asillustrated on Figure 4.14.


Figure 4.14 Integration of the methods for determining recurrence and submersion

Examples mapsThe flood hazard maps for Wallonia are produced as the outcome of the combination of maps showing fieldsurveys (occurrence of historical floods), extension of the floodplain and the results of a hydraulic modelling. Anexample of the resulting flood hazard map is shown in Figure 4.15.


Figure 4.15 Example of a flood hazard map from Wallonia (sub-basin Dendre)

Comments on the map

The general layout of the map forms an attractive combination based on transparent colours overlaying atopographic background map in grey scale. The choice of the colours on the example flood hazard map forWallonia are logic and intuitive, but it would be interesting to mention both a qualitative (‘low / medium / high’)and quantitative value (’25 / 50 / > 100 years’) for the hazard in the legend. The information provided on themap is also rather limited compared to other example maps in this Atlas.


4.3 Croatia

In Croatia a pilot project has been carried out for the preparation of flood risk maps for river basin managementpurposes in 2004. The maps are produced on a scale of 1:100.000. In the Figure 4.16 to Figure 4.21 the resultsare shown for the river Krapina subbasin.

Figure 4.16 Overview of the river Krapina basin


Figure 4.17 Extent of expected flooding for events with a return period of 5 years

Figure 4.18 Extent of expected flooding for events with a return period of 1000 years


Figure 4.19 Landcover flooded for events with a return period of 1000 years

Figure 4.20 Damage map for events with a return period of 1000 years


Naselja = settlements

Figure 4.21 Overview of expected extent of flooded area for various return periods

Comments on the mapsAlthough the overview map of the Krapina basin (Figure 4.16) is very nice from a cartographic point of view, itlacks a legend and as such it is not very informative. Similarly the two maps of the expected flood extension forreturn periods of 5 and 1000 years (resp. Figure 4.17 and Figure 4.18) do evidently show the difference floodedarea, but lack background information, e.g. a subset of the information provided on the overview map. On theother hand the map showing the expected flooded area for various return periods (5, 10, 25, 50, 100 and 1000years) does have a reasonable background, although in fact it only shows the basin limits and the drainagepattern. The information provided is difficult to judge as there is no clear measuring rod to read the actualdifference between the flooded areas for the various return periods. It does show very neatly the difference inflooded area between the upper basin (very large) and lower basin (relatively small), but this is simply a function ofthe size of those subbasins. It would be interesting to show the relative inundated area, i.e. as percentage of thetotal basin area.

Croatia is one of the few countries that provides flood damage maps and in Figure 4.19 and Figure 4.20 a landcover map and flood damage map are shown for the same river basin. In general the areas that are expected towitness damage during an event with a return period of 1/1000 years correspond with the flood extension map inFigure 4.18. In addition to that, although the flood damage map lacks a legend, it is evident that the darker redcolours correspond to higher expected damage as these areas coincide with the settlements (Naselja in Croatian)on the landcover map.


4.4 Denmark

In Denmark the Danish Coastal Authority has only published a few flood maps for specific study areas, such as theareas along the Danish West coast and the Ribe polder area (Wadden Sea region). Flood maps on the internet arenot available yet. Two examples of flood maps in Denmark are shown in Figure 4.22 and Figure 4.23.

Figure 4.22 A very extreme flood disaster event with a return period of 1/4000 yr in the Ribe polder area


Figure 4.23 A flood event of 1/100 yr for a dune area at the Danish West coast

Comments on the mapsIn Figure 4.22 both the expected inundated area and the infrastructure of the same region are shown. In thelegend, a distinction has been made between roads with a height of 3-6 m and those above 6 m, but it is not clearwhich of those roads might become inundated for the particular event (probably both, given that the situationrefers to a 1/4000 year flood). Such information might form the basis for an evacuation map. They roads are alsodifficult to distinguish on the map and the line for roads over 6 m might easily be confused with the ‘dike line’,although the latter is much more pronounced.

The map in Figure 4.23 is difficult to interpret for an outsider as it is not immediately clear on which side the sea islocated. The fact that the buildings on the right side of the map are inundated suggests that this is the land sideand the left side the coastal area which also becomes partly flooded during the event. This map would benefitfrom more background information on the map and in the legend and both maps lack a North indication and ascale rod.



4.6 Finland

In Finland many types of flood maps are produced which are summarized in the following table with an exampleof the layout of each of them.

Some flood map types used in Finland.

There are also many historical flood maps, i.e. maps showing the extent of historical floods. They can be used incombination with flood extension maps, but their use may be limited when referring to floods that occurred manyyears ago, especially in urban areas, as major changes may have occurred in the geometry of the river bed.


Figure 4.30 Flood hazard map for the city centre of Lapua for 1/1000 yr flood event


Figure 4.31 Flood hazard map of the city of Pori (water depths for 1/250 yr event)


Comments on the mapsThe flood maps from Finland are among the most complete and clearest examples that can be found. The mapsare available for various return periods. In Figure 4.30 an example is given for the city of Lapua in Western Finlandfor a flood event with a return period of 1/1000 yr. The layout of this map is very clear and easy to read also for anon-expert. It is also interesting that it not only gives the extent of the expected flooding, but also the maximumextent of the area that was incorporated in the flood modelling (with a green line), i.e. no information is availableoutside these boundaries. Isolated areas within the flooded areas are shown by hatching, but this is more difficultto distinguish on the map. The combination with type of urbanization makes the map useful as basis for flooddamage assessment. There is an inserted window to show the location of the detailed map and both scale andorientation of the map are very clearly indicated. All information on the background data of the map, includingthe basis for the delineation of the flood extension, is summarized in a table on the same map page.

For the flood hazard map that is shown in Figure 4.31 for the city of Pori the expected water depths are given foran event with a return period of 250 year. The map shows both the flooding of unprotected areas and, withshading, the areas that will be flooded in case of failure of dikes. It is assumed that all dikes will fail, i.e. it is aworse-case scenario. Also here the maximum extent of the modelled area is indicated by a green line.As with the flood extension map, at the bottom of the map, additional information is given, among which thebasis for the calculation of the corresponding discharge: frequency analysis with the Gumbel distribution. Thecorresponding water levels are calculated with a 1-D hydrodynamic model. Such information is rarely given withflood maps and it is often even difficult to find this type of technical background information in accompanyingdocuments.

It is also interesting that these maps show in a very prominent position a disclaimer in red: “The purpose of themap is to give a general view of the extent and depth of a 250-year flood. It is not reasonable to use the map fora building-specific analysing. More information: http://www.ymparisto.fi/.”. This is a very clear statement and itcan be assumed that this message will not easily be overlooked as might happen with disclaimers in separateinternet pages and/or accompanying documents. On the specified internet site, more detailed information isindeed provided (albeit evidently in Finnish) and more examples of flood maps can be downloaded.

4.7 France

France has interactive flood maps for various regions on the internet. A few examples are given below.

General informationIn the following figures first examples are given of four interactive internet sites that are available in France toobtain flood extension maps for different regions.

In Example 1 a nationwide system is shown that allows the user to access flood-related risk information for anumber of regions in France.

The other three examples are administered by different agencies and as such the layout of these sites is completelydifferent. The three examples are produced by different methods:• Example 2 – Carte Rhône river – region of Avignon: based on hydrogeomorphology;• Example 3 – Nord Pas-de-Calais: based on modelisation• Example 4 – Ile-de-France region: based on historical flood maps.

A fifth example of flood maps from France is produced by the insurance sector and therefore discussed separatelyin the corresponding Chapter 6.4.

Example 1 – Ministere de l’ecologie et du developpement durableAn interesting source of information on the risk of natural disasters can be found on a central internet site of theMinistère de l’écologie et du développement durable7. On this site, called ‘Cartoristique’ the risk of naturaldisasters has been centralized from various local sources. One of the main reasons for making this informationavailable to the public is the “Plan de Prévention des Risques naturels (PPR)”, which was created by the law of 2February 1995, and which includes evidently flood risk. The use of the risk information in the insurance againstfloods is further discussed in Chapter 6.4.


7 http://cartorisque.prim.net/index.html

Figure 4.32 Overview page of the nationwide risk internet site

On Figure 4.32 an overview is given of the regions in France for which risk maps are available (shown in darkblue, light blue means “not yet available”). Risks refer to a number of natural risks, including avalanches, etc., butfor this purpose flooding is only relevant. After choosing a certain region, a new map becomes available withinwhich by zooming the flood hazard along a river can be shown (e.g. Thionville along the Mosel river in Figure4.33). Depending on the choice of the region, the extent of a number of historical floods can be shown. Byclicking anywhere within a flood-prone region, additional information becomes available which shows that theflood extent refers to a flood with a return period of 1/100 years and it also makes a background documentavailable on the chosen location with an overview of historical natural disasters (in this case floods).

Comments on the mapsThe main advantage of this system is evidently that it uses a common layout for all the departments in France,despite the fact that different sources of information may be at the basis. The layout is straightforward and easy tounderstand, with both the detailed map with the actual required information and the overview map in the samewindow. There is, however, no indication on the maps themselves to which return period the flood risk map refers.The use of different historical floods makes it impossible to compare adjoining maps, but this is not a majordrawback. The use of the various map layers is well organized, with an indication that certain background layers,such as a scanned topographical map and orthographic (aerial) photos, can only be shown after the user haszoomed in sufficiently (Figure 4.34).


Figure 4.33 Example of a flood extension map for Thionville on the Mosel river


Figure 4.34 Effect of different levels of zooming in on the availability of background layers in the Cartorisque system

(Abbeville on the Somme river)


Example 2 - Rhône river – region of Avignon8

Figure 4.35 Example of flood extension internet site of the Rhone river region

Figure 4.36 Flood inundation maps for city of Avignon with both historical floods (1856 and 2003) and expected inundation areas


8 http://www.geomapguide.com/diren/Risques/Dynamap_risques.htm

Comments on the mapsThe layout of the interactive internet site for the Rhône river, and more in detail shown for the region of Avignonin Figure 4.36, is very attractive and easy to work with also for a non-expert. It shows a combination of historicalfloods (in this case 1856 and 2003) and expected flood extension. For the latter, though, there is no informationto which return period the indicated area belongs. The map was build on the basis of a topographic map with ascale of 1:25.000. There is a clear indication of the location of the detailed map within the overall region. There isno North indication, but in this case all maps are automatically orientated with North at the top of the map.Although it is interesting to show historical floods with the flood extension information, it should be remarked thatthe extension of floods in the 19th century, as in this case for 1856, may be of limited value given the fact thatmany changes may have occurred since that time in the geometry of the river cross-sections.

Example 3 - Nord Pas-de-Calais9

Figure 4.37 Example of the river Yser in Nord Pas-de-Calais

Comments on the mapsThe layout of the internet site for the Nord Pas-de-Calais (Figure 4.37) is clear and easy to interpret. In this casealso a combination is shown of historical floods (here a flood of 2001) and the expected flood extension for evenswith a return period of 1/10 yr (‘décennale’) and 1/100 yr (‘centennale’). There are also indications possible of thepreferential flow path and storage areas. The former may be used as indication where higher flow velocities can beexpected, although no flow velocity map is provided. Information on flood depth and duration of the flooding isgiven for isolated points (depth with green, duration with black) and this type of data is shown whenever such apoint is highlighted with the mouse. Depth is given with 0.1 m precision for the historic flood and the two returnperiods. The duration is given as an order of magnitude (e.g. 1 – 2 days), but there is no information on the mapto which return period this information refers.


9 http://carto.ecologie.gouv.fr/HTML_PUBLIC/Site de consultation/site.php?map = azi_yser.map&service_idx=24W htm

Example 4 - Ile-de-France region10

Figure 4.38 User-interface of the flood map site of the Ile-de-France

Figure 4.39 Detail of the flood inundation map for the Ile-de-France

Comments on the mapsFor the Ile-de-France region only historical flood extensions are given and it is only included here as an example ofa flood map of a very densely populated urban area (region Paris). Different historical floods can be chosen fromthe internet site.


10 http://carto.ecologie.gouv.fr/HTML_PUBLIC/Site%20de%20consultation/site.php?map=essai_PHEC.map&service_idx=18W

4.8 Germany

For Germany there are many different maps as each of the “Länder” makes its own maps, but recently (2006)recommendations have been published on national level for the production of flood maps11. Examples in thisdocument include maps from Baden-Württemberg, Bayern, Nieder-Sachsen (including Bremen), Nordrhein-Westfalen, Rheinland-Pfalz, Saarland, Sachsen and Sachsen-Anhalt.

4.8.1 Baden-WürttembergFor Baden-Württemberg there are interactive maps available for both flood extension and flood depth on theinternet12. However, there is still very limited information available (only the Neckar river between Mosbach andHeidelberg, see Figure 4.41). There is a clear corresponding document available in PDF-format directly from themap page in which the procedure is explained of the production of the flood maps. Information is given for returnperiods of 1/10, 1/50, 1/100 and an ‘extreme’ situation. The latter is explained in the text as a ‘statistically veryrare event. It can be defined as a historical event, which may be different for different locations, e.g. due toobstruction by bridges’. It is not possible to give any return period to such an event.

In Figure 4.40 the various concepts are shown that are used for the elaboration of the flood maps of Baden-Württemberg. Important are the possibilities to indicate whether a certain area is located behind a flood defenceand the return period for which this flood defence is still effective.

In Figure 4.41 the (restricted) river stretch is shown for which flood maps are made publicly available (Neckarriver). Examples of flood maps for this region are shown in Figure 4.42 and Figure 4.43. They can be accessedfrom the internet13. As stated on the internet site of Baden-Württemberg all the maps are produced as part of theEU-funded SAFER project (see Chapter 5.6). Baden-Württemberg has also produced an English-languageguidebook ‘Flood Risk Maps in Baden-Württemberg’, as part of the SAFER EU project, which forms the basis forthe production of the flood hazard maps. The map in Figure 4.43 is an example of a map that is producedfollowing these (SAFER) guidelines.


11 Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall (DWA), Arbeitsgruppe Hochwassermanagement:

“Empfehlungen der Bund-/ Länderarbeitsgemeinschaft Wasser (LAWA) zur Aufstellung von Hochwasser-Gefahrenkarten”12 http://rips-dienste.lubw.baden-wuerttemberg.de/rips/hwgk/13 http://www.hochwasser.baden-wuerttemberg.de/

Figure 4.40 Examples of the definition of flood inundation areas (Baden-Württemberg)


Figure 4.41 Location for which flood maps are available in Baden-Württemberg (Neckar river)

Figure 4.42 Example of a flood extension map from Baden-Württemberg (Neckar)


Figure 4.43 Example of flood depth map (Neckar river)

Comment on the mapsThe flood extension map (Figure 4.42) is rather detailed and easy to read. The inundated area for each returnperiod is shown as the increment compared to the lower return period, the results on the map being in line withthe intuitive interpretation that higher return periods result in larger (=darker hue of blue) water depths.

For the flood depth map (Figure 4.43) the information is only provided for the ‘extreme’ flood, which has no clearreturn period, although in the case of the maps shown above it corresponds with the extension of the 1/100 yearflood (possibly because no major historical flood information is available). The use of colours is unusual as normallyflood depth is only shown in shades of blue. The present succession from yellow to red is normally used in floodrisk maps to indicate increased level of danger. Step size of 0.5 m is logic and probably consistent with the level ofprecision of the underlying data.

4.8.2 Bayern (Bavaria)With the “Information Service on Flood Hazard Areas” detailed flood plain maps for Bayern are shown on theinternet14, open to the public. The service was published by the Bavarian Environment Agency in March 2004. Itcontains:− Flood plains (German: Überschwemmungsgebiete). Usually these areas are calculated for a 100 year flood by

means of hydraulic modelling and based on high-precision digital elevation models. Up to the end of 2008flood plain maps will be produced for all big and medium rivers in Bavaria (~ 9.000 river kilometres) in a scaleof 1:2.500 to 1:5.000. Furthermore the extension of the programme on small rivers is planned.

− Flood prone areas (German: Wassersensible Bereiche): Derived in a scale of 1:25.000 they represent anestimation of potentially hazardous areas by interpreting soil maps (natural flood plains). Water sensible areasare only developed for online presentation. As they are available almost all over Bavaria, they are provided asvery simple and basic information for the public, to assess the risk of flooding or high ground water level.

The integration of flood hazard maps into the web mapping service is planned. First pilot studies are alreadystarted.


14 http://www.iug.bayern.de

The internet site with an example for the region of Regensburg is shown in Figure 4.44.

Figure 4.44 Interactive internet site for flood maps in Bayern

Comment on the mapCompared to many other interactive flood map sites, the site for Bayern shows limited information and as such isof course also easy to interpret. The outstanding feature of the mapping service is the possibility to get verydetailed information on the extension of floods. With changing background map zooming in is possible up to ascale that shows every house and parcel (Figure 4.45). Thus utilization restrictions due to water legislation arecomprehensible for everyone. In the information provided on the map, it is indicated that the flood inundationarea normally corresponds with an event with a return period of 1/100 yr, but in some cases either 1/30 yr or1/300 yr. In a few cases it represents the extent of a historical flood and further inquiry may be necessary to clarifywhat the flood extent for a certain location means.


Figure 4.45 Detail of the interactive internet site precisely showing the affection of houses and parcels

4.8.3 Nieder-Sachsen / BremenFor Nieder-Sachsen and the city of Bremen flood hazard maps are available on the internet as downloadable mapsheets in PDF format15. An example is given in Figure 4.46. The legend to the maps is only available in German,but the expected flood extension for a return period of 100 years is shown in light-blue. Diagonal hatchingindicates regions for which the maps are still being produced, while dark-blue is used for flood water retentionareas. The city of Bremen is covered by two map sheets (nrs. 4 and 9). According to the accompanying text (inGerman) the inundation areas are calculated by 1-D hydraulic models and, for more complex situations, with 2-Dhydraulic models. The approach is based on a steady-state situation, i.e. no calculations are made of the actualinundation process and therefore no information is available on the duration of the inundation. Maps are given ona scale of 1:200.000. New detailed maps for some areas on a scale of 1:25.000 are also available on the sameinternet site and it is the aim to finalize the inundation mapping for the whole of Nieder-Sachsen in 2008.


15 http://www.mu1.niedersachsen.de/master/C7774004_N11348_L20_D0_I598

Figure 4.46 Example of flood map for Nieder-Sachsen with part of the city of Bremen

Comments on the mapThe flood hazard maps of Nieder-Sachsen are easy to read due to the combination of clear colours for theinundated areas and a topographical background. The information provided is limited, with only the expectedextension of the inundation without any indication of the expected depth. The legend is only provided on theoverall map with the location of the map sheets, no legend is available on the map sheets themselves. Such alegend is available, though, on the newly produced more detailed maps.

4.8.4 Nordrhein-WestfalenFor Nordrhein-Westfalen use is made of maps, which can be downloaded from the corresponding internet site16.Information on flood extension is given for the Rhine river for a return period of 1/500 yr and the smaller streamsfor 1/100 yr. The maps are available as PDF files and are very detailed. Interestingly the maps also show regionsthat may be used as emergency inundation areas. In Figure 4.47 this is shown with the normal flood extension indark-blue and the emergency inundation areas in yellow and pink. The yellow areas are flooded in for floods witha return period of 100 years in case no action is taken, while the pink areas are restricted region for inundation andonly used in special cases.


16 http://www.lua.nrw.de/wasser/hwberkarten.htm

Figure 4.47 Flood extension maps in Nordrhein-Westfalen including emergency inundation area

In Figure 4.48 an example is given of the Rhine river in the region of Köln that shows the expected inundationarea for an event with a return period of 1/500 yr for the Rhine, with a distinction between inundated area alongthe main river channel (light blue) and behind dikes (hatched yellow). For the tributary of the Sieg in the rightupper part of the map, both the expected inundated area for a return period of 1/100 yr is given as well as theemergency inundation area (in yellow and pink).The legend is rather small and not easy to read, even when printed on A3 format as in this case. This illustrates theproblem of reproducing scanned original topographic maps as background to flood maps.

The access link to an interactive map is already shown on the internet site where the maps of Nordrhein-Westfalenare available, but has not yet been activated.


Figure 4.48 Example of a flood extension map with indication of emergency inundation areas along the Rhine


4.8.5 Rheinland-PfalzRheinland-Pfalz has a very complete interactive map internet site17 for the Mosel basin with many possibilities foradjusting the map and searching for e.g. rivers, locations, etc. It is based on a high-precision elevation model. Theuse of river kilometres (in steps of 500 m) to focus on river stretches is particularly helpful. The map is used toshow information on expected flood extension (for return periods of 1/50, 1/100, 1/200 and ‘extreme’ events)and also for a second class of information (‘Danger classes’, with a distinction in four classes). It is possible to showthe four types of extension as well as the danger (or hazard) classes in one map, but evidently the information willoverlap and may be partly lost. Deriving the hazard stages is based on a method in which the degree of hazard isexpressed by the intensity (water depth and flow velocity) of a flood event in combination with the probability ofits occurrence. Using a hazard matrix - an intensity-probability diagram - these two parameters are summarised tobe expressed as hazard stages (see below).

The hazard stages show the degree of danger to persons, animals and property and are differentiated into threedegrees of hazard, distinguishable by the colours red (substantial hazard), orange (moderate hazard) and yellow(minor hazard). In order to be able to calculate the residual hazard, the hazard situation for very rare events(extreme floodwater run-off) was examined. These areas are shown as yellow-white hatched.

A similar approach with a hazard matrix is adopted in Switzerland and Belgium (Wallonia).

17 http://www.gefahrenatlas-mosel.de


Figure 4.49 Example of flood extension map for the Saar river

Figure 4.50 Danger class map of the lower part of the Kyll river

Figure 4.51 Flood extension map of the lower part of the Kyll river

The danger or hazard classes do not correspond with the flood extension classes and return periods. They aredefined based on the initiative of the international TIMIS-project (see Chapter 5.7) through which hazard maps formore rivers in Rhineland-Palatinate are elaborated. The maps will be available in the internet in 2008 and willprovide a lot more information for the user. The four danger classes that are used on those maps are furtherdiscussed in Chapter 5.7 on the TIMIS project. Figure 4.52 shows an example of an improved hazard map forRheinland-Pfalz.

Figure 4.52 Example of a hazard map for Rheinland-Pfalz



Comments on the mapsThe internet application for the Mosel river in Germany is among the most complete that is presently available.The layout is very clear and the information provided also very complete. The three examples of the internet siteitself (Figure 4.49, Figure 4.50 and Figure 4.51) show expected flood extension and flood risk according to theclassification explained above. It is possible to show both the flood extension and the risk level in one map,although sometimes the information will be obliterated. Return periods can be chosen (1/50, 1/00, 1/200 and‘extreme flood’) and the user can interactively change the details of the background information, includingvegetation, names of towns, etc. Colours are well-chosen and make it immediately clear to the user which areashave the highest risk. There are very easy to use search options, e.g. for a certain town and it is also possible tojump directly to a certain location along a river using river kilometre indications. This internet flood map site mightform an interesting example for other agencies that want to provide their information interactively.

4.8.6 SaarlandAlso the maps for the Saarland region are based on an interactive map site18. An example is shown in Figure 4.53.

Figure 4.53 Example of a flood extension map for the Saarland region (1/200 yr event)

Comment on the mapAlthough the map is rather clear, especially the topographical information, the large number of parallel dark-bluelines, indicating the limits of the expected flood extension for a 1/200 year event, may be more difficult todistinguish than the method based on coloured surfaces.

4.8.7 SachsenFor Sachsen there is an interactive internet site19 where a choice is given between flood inundation maps(Uberschwemmungskarte) and flood damage maps (Schaden¬potential¬karte). In Sachsen some major cities arelocated, such as Leipzig, Dresden and Chemnitz. Dresden is particularly interesting as it has witnessed major floodevents in the recent past due to high water levels on the Elbe river (especially August 2002, for which a historicalflood extension map is also available). It should be remarked that the maps have been produced as part of thetransboundary ELLA project (see Chapter 5.3).

18 http://www.gis.saarland.de/website/usg1/viewer.htm?Title=%DCberschwemmungsgebiete19 http://www.umwelt.sachsen.de/de/wu/umwelt/lfug/lfug-internet/interaktive_karten_10950.html

Flood extension mapsOn the flood extension maps it is possible to show expected flood extensions for three return periods: 1/20,1/100 and ‘extreme’, which according to the description is higher than any historical flood extent and at leastmore than 1/300 years. For the three return periods it is possible to show the corresponding expected floodextent, but only for the ‘extreme’ situation it is also possible to show the expected flood depth. Use is made of anintelligent map program that avoids ‘overlapping’ information, e.g. trying to show both extension and waterdepth, the latter showing evidently automatically already the extension. It is interesting that it is possible also toshow vulnerable locations such as hospitals, energy installations, water production and industrial areas. Theexamples are shown for Leipzig and Dresden (Figure 4.54 and Figure 4.55).

Figure 4.54 Flood extension map of the region of Leipzig

Figure 4.55 Flood extension map of the region of Dresden

Comments on the mapsIn general the use of the colour green for flood extension (and in this case use is made of hues of green to showthe flood extension corresponding to the three return periods) is unusual, but most likely has been chosen to allowfor the combination of both flood extension and expected water depth in the same figure. It should be remarked,though, that green is normally used to indicate safety, which is not the case in this map. This shows the conflict incolouring that will occur when several themes are shown in the same map.



Flood damage mapsThe layout of the flood damage maps is similar to the flood extension maps. Examples for Leipzig and Dresden areshown again (Figure 4.56 and Figure 4.57), but with a higher level of detail as in this case map layers with detailson the expected damage become visible.

Figure 4.56 Flood damage map of the region of Leipzig

Figure 4.57 Flood damage map of the region of Dresden

Comments on the mapsThese maps give very detailed information on the potential damage during ‘extreme’ floods, with a distinctionbetween industry and urban damage. Colours are well-chosen and evidently the user can change interactivelyboth the region and the scale that is wanted.


4.8.8 Sachsen-AnhaltFor Sachsen-Anhalt a number of very detailed maps are available on the internet20 in PDF format. In Figure 4.58an example is shown for the river Elbe at the city of Magdeburg for an event with a return period of 1/100 yr.

Figure 4.58 Flood extension map for the river Elbe at Magdeburg

Comment on the mapThis is an example of a very clear map, partly due to the limited type of information that is provided. They have adetailed topographical background. Flood depths are given in a non-linear scale (0.5, 1, 2 and 4 m), which maylead to confusion. Although the maps are freely available from the internet, they can not be copied or printed.

20 http://www.ella-interreg.org/gefahrenkarten0.html

4.9 Hungary

In Hungary flood maps have been produced for the major rivers, but most of the maps are rather old and have notbeen updated since 1977. Only flood extension has been presented.

Figure 4.59 Flood map of the Tisza river basin


Figure 4.60 Flood map at Madocsa on the River Danube in Southern Hungary

Comments on the mapsIn Figure 4.59 example of a flood extension map is given for the Tisza river. The example is the version in scale1:500,000, but the maps are originally made in 1:50,000 and 1:100,000.Although it is originally called flood hazard map, it shows the expected flood extension for return periods of 1/100and 1/1000 yr. The map is an example of a flood extension map without any special additions and as such is veryeasy to interpret.

A map of a Danube flood area in 1:50,000 is shown in Figure 4.60. The same return periods are used at thisexample and also the flood embankments are shown. Flood embankments are very important in Hungary: about97% of the floodplains are protected by dikes.

Recently new flood maps are being prepared and will become available for the whole country in the near futurebased on statistical analysis. In many cases hydraulic modelling is used to determine the flood extent, flood depthand the propagation time of inundation. The processing of new flood maps for Hungary is still in progress. In thefuture many other types of flood maps will be available, among which flood risk and flood damage maps.Examples of new flood maps for Hungary are shown in Figure 4.61 (extension of inundation), Figure 4.62 (flooddepth) and Figure 4.63 (propagation of inundation).


Figure 4.61 Bereg flood area, River Tisza right bank, highest elevations of inundation (masl Baltic)

Figure 4.62 Bereg flood area, River Tisza right bank, flood depth (m)


Figure 4.63 Bereg flood area, River Tisza right bank, propagation of inundation (hours)


4.10 Ireland

In the past flood mapping in Ireland has focused on mapping of flood extents for various event probabilities(return periods) only in high-risk areas. This practice has recently been expanded to include the mapping of floodvelocities and depths (See Figure 4.64) based on 2-Dimensional hydraulic modelling and high-resolution digitalterrain models.

Figure 4.64 Flood depth map – 1% Annual probability event

A national flood mapping programme has been initiated to provide greater spatial coverage of flood maps,principally for planning and development management and flood risk management planning. Phase I of thisprogramme has recently been completed, with the development of a web-based information managementsystem, and its population with collated and verified historic flood data (www.floodmaps.ie, see Figure 4.65).Before the user can enter the internet site, a disclaimer has to be acknowledged:

The user can search on the name of a location or zoom in on the map and interactively choose a location. For eachlocation for which specific information is available a clickable indication in the form of yellow triangle is shown onthe map. As is shown in Figure 4.65 for each location the available information on historic floods is given, whichcan be accessed directly on-line, also reports on the event. There is also a complete glossary on the technicalwords and an extendable legend.


IntroductionThe Office of Public Works (OPW) is the leading state agency in relation to flood-related matters in theRepublic of Ireland. The information in relation to past flood events that is displayed on this Web site iscollected by OPW from Local Authorities, other state bodies and members of the general public. Theinformation is then put through a rigorous verification process in order to provide the maximum degree ofconfidence in its accuracy. However, due to the type and character of the information involved there are anumber of issues and considerations that users should take account of in relation to the Content and the Useof the Web site.

Figure 4.65 Website view, indicating historic flood extents and reported flood incidents

In addition to historic flood extent and incident locations, the website also makes available to the user informationsuch as photographs (see Figure 4.66), reports, hydrometric data and other supporting information.

Figure 4.66 Website view, available photographs of historic flood events

Predictive flood maps currently under development through the flood mapping programme will also be madeavailable via the website. The foreseen format of the flood extent maps is provided in Figure 4.67. It might benoted that the line type varies for different reaches of each of the flood envelopes to indicate a high, medium orlow level of confidence (indicator of uncertainty) associated with the flood extent. A table of flood levels (abovedatum) is also provided for nodes along the river channel.


Figure 4.67 Predictive flood extent mapping format, with indicator of uncertainty and table of flood levels

(Note: Map is provided only as example of map format)

Comments on the mapsAt present Ireland has one of the most sophisticated interactive internet sites to access information and maps onhistoric flood events. The combination of both documents, photos and maps makes it very easy for the user to geta complete picture of the situation.For flood extent maps at present only maps for high-risk areas are available, which though are easy to read with awell-chosen range of colours for the various levels of risks. For the whole of Ireland, the work on flood mapping isstill in progress, but the example provided shows that these maps are also easy to read and the use of coloursintuitive.


4.11 Italy

For Italy a number of flood-related maps have been made available. However, no information has been providedon the mapping programme, mapping authorities or any other background information.

Figure 4.68 Flood extension and risk map in Italy (location Rieti)

On the flood extension map (Figure 4.68) both the flood extension is shown (for 3 return periods: 1/50, 1/200and 1/500 yr) and three levels of risk (R2, R3 and R4). This risk factor R is defined on the basis of two parameters:sensitivity and probability. One of these two factors (probability) is already shown on the same map (inverse of thereturn period) and the risk factor is obtained by overlying this information with land use and urban planning. Thelatter is remarkable, because it implies that future urban layout is taken into account. In total there are four levelsof risk (R1 – R4). Risk area R1 is characterized by a low sensitivity, because its specific use implies a low probabilityof human loss or because it falls within areas characterized by high return periods. The level of risk increases fromR4 to R2:• R4: Return period of 1/50 yr and high level of sensitivity• R3: Return period of 1/50 – 1/200 yr and high level of sensitivity• R2: Return period of 1/200 – 1/500 yr and high level of sensitivity

The process of derivation of risk areas is shown in Figure 4.69 - Figure 4.71 for the river Tevere with a totalpopulation of about 4.3 million persons. The Tevere river passes through the city of Rome towards theMediterranean Sea and as such is a very relevant example of flood mapping in an urban area.

On Figure 4.69 the vulnerability / sensitivity is indicated of exposed assets (i.e. types of buildings, sport facilities,waste dumping areas, power plants, etc.). In the vulnerability maps, red indicates the most vulnerable locations,which is logical. However, green indicating the least vulnerable locations might suggest that these areas are safe,which is misleading.


On Figure 4.70 the flood extension for the three return periods is shown. Use is made of colours that are normallyassociated with a danger level, e.g. red is used for the flood with the highest probability (1/50 years) that can beexpected to have the highest water depths and flow velocities.

On Figure 4.71 the combination of the two former maps into a flood hazard map is shown. Use is made of thecolour red again for the highest flood hazard.

Figure 4.69 Vulnerability of exposed assets in the river valley of the Tevere

Figure 4.70 Flood extension map for 3 return periods (1/50, 1/200 and 1/ 500 years)


Figure 4.71 Hazard map (combination of vulnerability and flood extension maps) for 3 return periods

Comments on the mapsThe maps for Italy give one of the scarce examples of flood risk maps (probability versus consequences). Themethod is easy to understand, but the use of the same colour (e.g. red) for high vulnerability and high probabilitymight cause some confusion.In addition, the use of green for areas of low probability c.q. vulnerability may lead to the misleading conclusionthat those areas are safe, while this is not the case.




7.2 Japan









7.3 Netherlands




exits



7.4 USA



4.12 Latvia

Latvia doesn’t yet have a well established flood mapping system, partly because there was no urgent need forsuch mapping for the whole of Latvia or separate river basins. For historical events maps are available as hardcopies. Many maps are produced on special request e.g. for a municipality.

In Latvia there is no great flooding as in most of other European countries where larger rivers are present.However, some flood mapping efforts are made mostly if there are requests from municipalities. Calculations aremade for some territories for 1/100 yr (1% probability) and sometimes other frequencies (5%, 10%, 20% or 50%probability etc.), depending on request.

For the examples of flood maps in Latvia two maps are available. The map in Figure 4.72 shows the expectedflood extent for an event with a return period of 1/100 yr for the city of Jekabpils, which lies along the Daugavariver, which is the most important river in Latvia. Most floods in the city of Jekabpils occur in spring due to ice-jams.

The map in Figure 4.73 shows the flood extension for the city of Lubana on the Aiviekste river, a tributary of theDaugava river, also for a return period of 100 years. This is an example of a map that was especially produced fora municipality, who requested also to have land use on the same map.

Both maps where made in Latvian Environment, Geology and Meteorology Agency (LEGMA) in year 2006. Itshould be remarked that the layout of both maps map is rather clear and easy to read.

Figure 4.72 Flood extension map for the city of Jekabpils in Latvia on the Daugava river


Figure 4.73 Flooded area (diagonal blue lines) for the city of Lubana for a return period of 100 years


4.14 Netherlands

The Netherlands is flood prone for about 60% of its surface. 95 so-called dike-rings protect the polders from beingflooded from the North Sea, rivers or lakes. The protection level has a legal status, expressed in the followingexceedance frequencies per year: 1/10.000 along the central section of the North Sea coast, 1/1250 along themain rivers, 1/2000 and 1/4000 in the intermediate estuaries, lake IJssel and Wadden Sea. Flooding of these dikerings may occur as a result of the failure (or overtopping) of embankments or other defence works (sluices, stormsurge barriers). Under these conditions a relatively large area may be flooded in a couple of days. The extent,progress and final flooding depth (and hence potential damage and affected inhabitants) depend on the locationand process of the failure, hydraulic boundary conditions and terrain characteristics. This can be simulated by 2-Dmodel computations. Only relatively small, unprotected areas outside these dike-rings experience the naturaldynamics of rising waters due to the tide, storm-surges or river floods. Along the river Meuse isolated villages haveminor embankments with a protection level of 1/250.Official flood (extent) maps in the Netherlands are available for public and official use on Internet(www.risicokaart.nl, access on provincial level). These maps show flood prone areas, as defined by more than 1meter flooding depth with a frequency larger than 1/4000 per year. Figure 4.76 shows an example for theprovince of Gelderland. Many types of disasters are shown on this site, including accidents in tunnels, traffic, forestfires, earthquakes etc. To show maps related to floods (the light blue horizontal hatching), the other options cansimply be turned off.In addition to these official maps many types of flood maps exist for study and disaster management purposes. Asa result of these studies a new generation of flood maps will become available on the provincial Internet-sites thecoming years. Anticipating the EU Flood Risk Management Directive these maps will distinguish between floodextent, depth and probability, flood progress (and rate of rise), dangerous current velocities, potential damage andaffected inhabitants, flood risk (probability x adverse effects) and finally information for evacuation.

Figure 4.76 Interactive flood risk map of a part of the province of Gelderland in the Netherlands


Figure 4.77 shows, for the Netherlands as a whole, the maximum depth of flooding for any location that mayoccur due to embankment overtopping without any reference to return period. As such it does not represent a realsituation, but the worst case for every location.

Figure 4.78 and Figure 4.79 show examples of depth and potential damage for a specific event: a flood caused byfailure of the coastal dunes between The Hague and Rotterdam by a specified North Sea storm surge. Increasingflood depth (and damage) is visualized by increasing intensities of blue (and red). Maximum flood depth anddamage not necessarily coincide. Of course damage only occurs where flooding occurs, but the amount ofdamage is much more determined by socio-economic value of a specific location than the expected depth ofinundation.

Figure 4.80 shows the travel time of the flooding process. This is important information for the preparation ofevacuation plans by disaster management organizations.

Figure 4.81 is an interesting example, as it shows flood depth classes related to the height of a human body (darkblue: ankle-deep, light blue: knee-deep, light rose: hip-deep, orange: head-deep, red: submerged).


Figure 4.77 Flood depth after inundation in the Netherlands at any location


Figure 4.78 Example of maximum flood inundation depth caused by sea flooding in the Netherlands


Figure 4.79 Potential flood damage resulting from flood depth and land use


Figure 4.80 Map showing the progress of an inundation front from dike failure at the coast of the Netherlands


Figure 4.81 Flood hazard map with indication of expected water depth with ‘human’ terminology

Another example of the information that can be obtained from series of simulations of the inundation process isshown for the region of ‘Land of Maas en Waal’ in the Netherlands in Figure 4.82 (time of arrival of front ofinundation with a depth of 50 cm) and the rate of rise of the water (Figure 4.83). The rate of rise has a majorimpact on the number of casualties, especially for inundation depths between 0 – 1.5 m. The highest values of therate of rise occur evidently close to the locations of dike failure (green dot). A combination of such a map with amap of population density and expected inundation depth can be used to derive an image of the potential numberof casualties in an area vulnerable to floods.


Figure 4.82 Inundation front arrival time for depth of 50 cm

Figure 4.83 Example of a map showing rate of rise of the water (m/hour)


21 http://wwf.pl/powodz/publikacje/hoydalflood.pdf


4.15 Norway

The map shown in Figure 4.84 is part of a program that was started after Norway suffered from a major floodevent in 1995 which caused extensive damage (approx. 225 million Euro). An extensive flood zone mappingproject was governmentally launched after this event. After a pre-study a total number of 134 sites were selectedfor detailed flood zone mapping. These are the most flood prone and most densely populated areas of Norway.The program ends in 2007, and then all the 134 flood zone maps will be finalized. The maps are published on theinternet and paper copies are also available together with the report. These are handed over to the localauthorities. The maps are important premises to local land use planning. The local land use planners are bound bythe maps from a legal point of view. The project has awakened the local authorities and new sites will be mappedin the years to come in a following up project. More information on the flood mapping procedures in Norway isgiven in a document on the internet (“Procedures And Guidelines For Flood Inundation Maps In Norway”21).

Comments on the mapThe example of the flood zone map for Norway is an interesting combination of a map sheet with additionalinformation. In the subtitle to the map it is clearly stated to which return period the map refers (here 1/100 yr) andthe legend is very clear. On the map sheet there is not only information on the flood extension, but also on thevulnerability of the buildings in the region, e.g. “Buildings with potential damage to basement”. Detailedinformation is provided on technical details of the map, date of the flood calculations, name of the correspondingreport, etc. In separate windows extra information is given on expected water levels at a cross section for otherreturn periods (1/20 – 1/500 yr) and the water profiles along the length of the river axis. There is a very clearindication of the location of the detailed map and the North of the map is also indicated. Although much of theinformation is provided on this map, most of it is probably only useful to a flood expert. In general, though, it isprobably one of the clearest flood map layouts at present available.

Figure 4.84 Flood zone map from Norway

4.16 Poland

For Poland both ‘traditional’ flood maps are available as well as interactively produced maps using Google Earth asbackground.

“Traditional” flood maps

Figure 4.85 Flood extension map in Poland

Explanation of the legend:Strefa zalewów o prawdopodobieństwie przewy�szenia p = 1% - flood zone with the exceedence probability p=1%

Istniejace wały powodziowe – existing levees


Figure 4.86 Flood extension and depth map at Wroclaw for Motorway A1 Study

Comment on the mapsThe flood extension map in Figure 4.85 is easy to read and as it provides only the expected flood extension forone event the information is straightforward. In Figure 4.86 both flood extension and depth are given, withoutcompromising the readability of the map.

The flood extension map shown in Figure 4.87 is very detailed, but the aim to show expected flood extension forseven return periods in the same map leads to an image in which it is not easy to distinguish the various lines thatshow the borders of the flood extension for each return period. It may be interesting to use coloured surfacesinstead of lines, showing the increment in inundated area for each subsequent return period.


Figure 4.87 Flood extension map for various return periods


Explanation of legend:

Granice zalewów o prawdopodobiezstwie przewy szenia

p = 0,2% …50%

- flood zone boundaries with the exceedence probability

p = 0,2% … 50%

Obszary bezodpływowe – non - runoff areas

Obszary osuwiskowe – landslide areas

Erozja brzegowa – bank erosion

Powiaty – counties

Gminy – communities

Rzeki – rivers

Wały przeciwpowodziowe – levees

Budo wle pietrzace (jazy, zapory)

– hydrotechnical structures (weirs, dams)

Przekroje poprzeczne – cross-sections

Zlewnia 1 .. Iv rzedu – 1st . .. 4th grade catchment

Kilometraz rzeki – river mileage

Sterunki wodowskazowye– gauging stations

Posterunki meteorologiczne – meteorological stations

Mosty – bridges

Sluzy wałowe – embankments sluices

Zbiorniki retencyjne, poldery – reservoirs, polders


Google Earth based flood maps

Figure 4.88 Flood extension map using Google Earth

Figure 4.89 Detail of flood extension map with Google Earth

Comments on the mapsThe use of Google Earth as a basis for mapping purposes is becoming more usual, e.g. in showing weather radarand many other spatial phenomena. An excellent example is now available from Poland. On Figure 4.88 andFigure 4.89 flood maps are placed on top of the photo-images of Google Earth. The procedure to transfer GIS-based flood maps to Google Earth is rather straightforward and the resulting ‘*.kmz’ files can be read immediatelyby Google Earth, who places the flood map information exactly upon the right location. In general this way ofpresentation is very good to provide information to the non-specialist, because it is easy to operate and a lot ofextra information can be made available by using links to other internet sites. In the document accompanying theGoogle Earth images the following advantages and disadvantages are mentioned:

Advantages:• Attractive image• Easy to operate, similar to net browsing• Large amount of information possible, especially when using www sites links• Easy and fast to convert data from existing ArcGIS geodatabaseDisadvantages:• A fast computer with Windows XP is required• A fast internet connection is required• Data presented in *.kmz file is given free of charge to the user, who can download the kmz.* file to the local

hard disk, so it not possible to use it for restricted data• It is possible to edit *.kmz data, but there is no connection with the geodatabase and the changes will not

appear in it• If many *.kmz files are placed in the ‘favourites locations’ map, Google Earth will operate slowly.

In addition it should be mentioned that there exists the risk that people will zoom in towards their own house /property and consider the flood information provided at this level as reliable, which may not be the case (seeChapter 3.2).

There is another possible disadvantage that might be less evident with Google Earth recently released and still indevelopment is the continuity of this service. This has been explained already in Chapter 3 on the cartographicaspects of flood mapping.



4.17 Spain

CataloniaIn Spain, inundation studies are the responsibility of the respective Hydrographic Confederations of each riverbasin (River Basin Authorities). The actual status of inundation studies varies from basin to basin with significantdifferences in the level of achievement.

A good example of inundation studies is the one corresponding to river basins in Catalonia, where theGovernment of Catalonia (Generalitat de Catalunya) through the Catalan water Agency has elaborated ainundation management plan, Inuncat22, where all the inundation areas corresponding to rivers in Catalonia havealready been produced.

The Catalonian Water Agency (Government of Catalonia) has evaluated for the river basins of Cataloniainundation maps for the main river courses (Delimitació de zones inundables a les conques internes de Catalunya)as well as for the Ebro river (Delimitació de zones inundables a les conques de l'Ebro) which has a basin sharedwith other regions. These studies define the inundation areas for return periods of 1/50, 1/100 and 1/500 yr23

and, also delineate potential flood areas from the geomorphological standpoint. In addition to this, the study alsoincludes a database with critical points, which are defined as locations where the experience acquired during manyyears of river management has shown that they present repeating problems24.

The inundation maps for return periods of 1/50, 1/100 and 1/500 yr (Figure 4.90) are interactively available inPDF format. In the example shown here, corresponding to the Besós river (the Northern natural border of the cityof Barcelona) only a part of the total map is shown and the legend has been placed on top in order to show onlythe most relevant information.

In Figure 4.91 an example is shown a flood hazard map for the Besós river basin at the northern part of the city ofBarcelona, with a part of the legend shown above. These maps are also available as PDF files directly from theinternet25. Also in this case this is only a part of the total map; the original full sheet includes information on themap and a clear indication of the location of the map area within the total province of Catalonia. In this case, thereis no indication of the return period that is represented in the map, because they delineate potential flood areasfrom the geomorphological standpoint using historical information (areas already subjected to floods) or geologicevidences. Use is made of signs in green, orange and red to indicate level of low, medium and high risk (seelegend).

22 http://mediambient.gencat.net/aca/ca//planificacio/inundabilitat/inici.jsp23 http://mediambient.gencat.net/aca/ca/planificacio/inundabilitat/delimitacio/pl_periode.jsp24 http://mediambient.gencat.net/aca/documents/ca/planificacio/inuncat/conquesinternes/punts_critics.pdf25 http://mediambient.gencat.net/aca/ca/planificacio/inundabilitat/delimitacio/pl_potencial.jsp


Figure 4.90 Flood extension maps for the Besós river basin (N of Barcelona) for 3 return periods

Figure 4.91 Flood hazard map for Besós river basin (N of Barcelona) for 3 return periods

Comment on the mapsThe layout of these maps is very clear and it is also relatively easy to distinguish between the three return periods.From the maps it is clear though that emphasis is placed on the presentation of the flood extension for a returnperiod of 1/50 yr, which is shown both with a bordering line as well as with a hatched surface. The use of red forthe lowest return period (1/50 yr) is chosen not to indicate the highest danger, but the highest risk of occurrence(i.e. the highest probability).

In Figure 4.92 a full flood hazard map is shown of a part of the Spanish coast in order to show the general outlineof such a map, which when printed on a larger scale result very clear and easy to read.


Figure 4.92 Full image of a flood hazard map in Catalonia

Obrir el Pànol de delimitació hidràulica


English translation of legends

Type/level of hazard Level of affectation

Low effects on an area

Medium effects on a stretch

High Critical point / hot

spot (e.g. bridge)

effects on large areas

Description code

AA: river or creek

BB: municipality

NN: number of order of hazard

From top to down:

Legend Geomorphology Symbols

Flood hazard area

Embankment area

Limit of historical flood area

Mark of recent movements

Active cone of dejection = floodable

Possible flow direction or water flow

Flow deviation due to existing anthropogenic

actions

Flood retaining wall

Mark of alluvial erosion / old meanders

Former lagoon/ dried deltaic lagoon or wetland

Northern Spain

In the Spanish northern basin, 38 384 km2 of total area, 2 900 129 inhabitants use intensively the scarce plainsurfaces, mostly associated to floodplains. The geographic and geological characteristics of the Cantabrian Rangeprovide an environment where rivers typically have high gradients with straight, short and incised channels, and itsdischarges are high in amount, velocity, erosive power and load of sediments. Another important characteristic isthe quick response of these rivers after rainfall.An approach to river activity in its floodplain can be obtained by geomorphic evidences studied by theGeomorphology as the science of landscape forms. As a result, the floodplain is divided in different terrace levelsassociated to different flood frequency, mostly restricted by steep banks and cliffs, and also defined by the floodshistoric analysis. This method, based in real evidences caused by floods, is especially useful in fluvial systems whererivers are confined within high valley walls and where the floodplain external limit is highly abrupt.

The first step is to define the study area by delineating the alluvial plain limits and the channel course withtopographic criteria and helped by aerial photos. An analysis of a series of historic photographs could help tounderstand the river behaviour during the recent past. It is necessary to take note of fluvial system properties aschannel width, margin height, steep or gradual margins, granulometric measures, etc. Furthermore, the main pointis to map the geomorphic elements of the alluvial landscape that are mentioned later. GIS software is an essentialtool because it allows to map and store all the information for its representation in flood maps or to be used later,for example, in emergency plans.

Historical information of flood events has been obtained from documentary sources and field interviews with localresidents. The former allow the identification of the main locations with flood problems, the latter provide moreaccurate data about the extent and characteristics of the events. In bibliographical literature and newspapers aninventory of sites historically affected by floods was collected for the time period 1522-2007 in an intensiverevision of nearly 7300 newspapers. The low precision of the historic floods data obtained in the previouscompilation forced to realize 2000 field interviews to local residents distributed in 340 km2 of floodplains. Dates,extent, damage (agriculture, buildings, roads links, etc.), water depth, grain size and sedimentation areas andoverflow zones were recorded. All this information was stored in a database, including photographs and videos ofsome floods and data of gauged flow and rainfall of every event when the information is available.


Information obtained from documentary sources (1 and 3) and field work

(2 and 4).

Example of event map in a section of the Arnoia river (Galicia, NW Spain)


Geomorphological evidences of floods are erosive or depositional landforms or other indicators of fluvial activity:• Channel course as a sign of the different fluvial energy among straight, meandering or braided rivers.• Steep banks or cliffs: linked to the main channel, to secondary channels or isolated in the floodplain.• Overflow point within we can think about water course throw the floodplain.• Recent deposits (characterization): levees, crevasse splays (granulometric fractions help to understand the flood

energy).• Microtopographies are identified as an irregular topography in the floodplain, at different scales, as a result of

the combination of erosive and deposited forms (negative and positive forms).

Natural narrowings or river confluences create important local variations of the fluvial energy.

Evidences of different floods frequency: 1 and 2 flood deposits, 3 microtopographt, 4 crevasse and overflow point and 5 steep bank defined by a

cliff.

The hydrological behaviour of rivers can be altered by different anthropic elements which have to be identifiedand described: human-made conflictive points, canalizations, reservoirs, others.

All field parameters are analysed by searching overflow points and its relationship with the observed geomorphicevidences. Also, zones with different fluvial activity, based on the geomorphic analysis, are linked to anapproximate return period by comparison of event properties obtained from the historic analysis (surface occupied,speed, swept sediments, overflow points, etc.). A good practice is to carry out a regional analysis in order to checkif the followed criteria were homogeneous in the entire basin and also to compare present floods.


Finally, all the information is used to distinguish different units represented in the flood map:

Low Terrace: it is the most active floodplain terrace flooded at least once every 10 years so it is plentifully ofgeomorphic evidences.

Middle Terrace: higher than the low terrace, it is associated to a flood frequency of once every 50 years.

High Terrace and Very High Terrace: with a flood frequency of once every one hundred years and five hundredyears respectively. They are short of geomorphic evidences and human activity is highly intense.

Example of a floodplain zonification in a section of the Narcea river (Asturias, NW Spain) with fluvial and torrent floods.

Other floods can be mapped as Tidal influence, mountain torrents an also drainage deficiency caused by artificialelements in the floodplain.

River flood risk determination has been carried out combining flood hazards mapping and land use vulnerability.Additionally, the risk map provides supplementary information about mountain torrent hazard, tide dynamics anddrainage deficiencies, and also it includes an inventory of assets at risk in the analyzed river sections.Vulnerability maps show different classes established regarding land use and a combined indicator which takes intoaccount material loss (direct and indirect economic vulnerability, VED and VEI), loss of life (population vulnerability,VP) and the reaction capacity decrease and services provision interruption (community vulnerability, VC), plus thepossible damage of Cultural Monuments protected by the regional government.Vulnerability and flood mapping are combined in a GIS in order to obtain different categories of flood risk: verylow, low, medium, high and very high, which are displayed in a 1:5.000 scale topographic map.


Flood hazards (left) and Land-use (right) maps of the Caudal river floodplain through the city of Mieres (Asturias, NW Spain)


Vulnerability map of the Caudal river floodplain through the city of Mieres (Asturias, NW Spain) used in the risk estimation.

Flood risk map of the Caudal river floddplain through the city of Mieres (Asturias, NW Spain)


4.18 Sweden

Swedish risk management programs are lead at local level. Sweden has chosen the “bottom up” approach tomake sure that all risks are addressed on the basis of the resources that are available. Risk assessment has to bedealt with locally due to the fact that accident and hazards occur locally - every accident/hazard has a geographicposition but the effects of the accident/hazard may be of local, regional, national or international character.Therefore, the subsidiary principle is the key factor in Sweden’s risk management policies. The Swedish CivilProtection Act supports this view.The Swedish Rescue Services Agency (SRSA) is the government authority tasked to improve safety againstaccidents within society. Among other things, the agency works with risk assessment and risk management inseveral different sectors, for example, natural disasters.SRSA mainly supports rescue services and municipalities with knowledge and subsidises preventive measures in thebuilt up environments that may be at risk of flooding and landslides. The SRSA also has the responsibility, oncommission from the government, for providing the municipalities and county administrative boards with generalplanning information such as general stability maps and general flood inundation maps. Flood risk assessment is amunicipal responsibility.

The Swedish Rescue Services Agency (SRSA) is conducting a general mapping of parts of Sweden’s waterways.The mapping began in 1998 and the goal is to achieve maps of approximately 10,000 km (approx.10%) ofSweden’s waterways. In January 2007 almost 8 000 km are mapped and 56 of the rivers are covered with FloodInundation Maps. 5 new rivers are going to be mapped in 2007.The general maps are intended for the overall planning of fire & rescue service work and as information for land-use planning. The flood mapping covers natural floods in both governed and ungoverned waterways, but notfloods that occur, for example, as a result of a dam break or an ice-dam.

The priority is made by a preliminary risk assessment based on risk identification and urbanized areas along therivers together with records of occurred flood events in the past.

In Figure 4.93 an overview is given of the rivers for which interactive maps are available now. The maps can beaccessed through a map browser on the internet26, showing the same map as in this figure, by clicking on aregion. This loads the corresponding PDF document. Both the internet site as well as all the texts accompanyingthe maps are only available in Swedish.


26 http://www.raddningsverket.se/templates/SRV_ExternalPage___2257.aspx

Figure 4.93 Flood Inundation Mapping in Sweden

Flood Inundation Maps highlight the areas that are at risk from flooding during two known high water discharges.Two types of flood are used:• the 100-year flood• the highest estimated flood.

The latter is calculated in accordance with the Swedish Flood Committee’s guidelines for the dimensioning of dams(dams in risk class I). The calculation is made on a systematic combination of all the critical factors (rain, melting ofsnow, levels of ground moisture, and the filling of basins in governed waterways) that contribute to a flood. Thecalculated return period is approximately 10 000 years.

Map productionThree elements are involved in the production of flood maps:• Calculation of the two floods. The 100-year flood is calculated by the statistical analysis of observed water flowmeasurements. The highest estimated flood is calculated in accordance with the Flood Committee’s guidelines.In the latter case a hydrological run-off model is programmed with maximum adverse conditions as regardsprecipitation, melting of snow and ground moisture conditions, while at the same time giving consideration topossible waterway governing and dam basin activities.

• Calculation of the water level along waterways during the two floods. This is achieved using a hydraulic model.The description of the waterway and stretch of river is achieved with the help of dam and bridge diagrams, and


looking at the qualities of the waterway and the topography of the surrounding land. The model is calibratedagainst previous measurements taken of the water level and flow. After which the water level across sections ofthe waterway is calculated.

• Mapping out of flooded areas along stretches of waterway. This mapping out is achieved with the help of ageographical information system (GIS). The water level along the whole waterway is interpolated and with theaid of a topographical database and Digital Elevation Model (DEM) the area that will be flooded can becalculated.

An example of a flood inundation map from Sweden is shown in Figure 4.94.

Figure 4.94 Example of a Swedish flood inundation map

Fields of applicationsThe mapping out work is presented partly in a report with printed maps and partly as GIS-layers for further workby users in the municipalities, county administrative boards etc. The idea is that the overlays shall be connected toa suitable map (e.g. 1:50,000) that shows where floods can occur and suggests likely problems with roads, railwaylines, bridges and buildings. The map overlays can also be connected to various co-ordinate registers, such as, forareas sensitive to landslides, property registers detailing numbers of inhabitants, wells, sewage treatment works,industries, environmentally hazardous operations, warehouses etc. Examples of the combined use of flood hazardand land use information are shown in Figure 4.9527 and Figure 4.9628. The former shows the flood-affectedroads, while the latter shows the occurrence of quick-clay areas at risk of flooding. These two maps are examplesof dedicated maps that combine flood inundation information with other types of information and therefore thecolour setting of the maps are also completely different.


Legend:

Highest estimated floodaccording to the Swedish FloodCommittee

100 year flood

Urban area

27 Source: Swedish Rescue Services Agency and County Administrative Board of Västmanland28 Source: Swedish Rescue Services Agency

Figure 4.95 180 km of roads at risk of flooding

Figure 4.96 An overlay analysis of the General Stability Map and the General Flood Risk Map

Comment on the mapsIn the flood map on Figure 4.94 the expected flood extension is shown for two situations (pink area = area at riskof 1/100 yr flood, hatched area = area at risk of 1/10,000 yr flood, grey area = area of municipality). The use ofthe latter return period is unusual and as expected the corresponding flood extensions are large. The colour pink isnot common for flood extension, but it does stand out very clear in both maps.In the map of the flood-affected roads (Figure 4.95), it is not clear what is meant with the red lines (floodextension ?) and the dark-blue double lines, although the latter probably represent those road sections.


4.19 Switzerland

In Switzerland several types of flood maps are produced. They include flooding (dynamic and static), debris flowactivity and bank erosion/scouring. Flood indication maps (flood extension maps) are produced on a scale of1:25,000 for the bigger cantons as shown in Figure 4.97. The maps represent an extreme event (generally setequal to a return period of 1/1,000 y) to get a quick insight in the most critical areas (by overlaying the vulnerableelements on the flood areas).

Figure 4.97 Example of a food indication map for an extreme event

Flood hazard maps are produced in a scale of 1:5,000 for return period similar to those used in Austria (1/30,1/100, 1/300, extreme event; the latter is not available in Austria). By combining the probability and the intensity(magnitude), the latter expressed as flow velocity or depth, the flood hazard class is obtained as indicated in Figure4.98.


The criteria used for the definition of flood hazard are given in detail in the following table.

Criteria for intensity of different hazards

Figure 4.98 Assessment of flood hazard in Switzerland

In Figure 4.99 an example is shown of a flood hazard map in Switzerland. Note that the processes represented inthis map are debris flows and related phenomena. The meaning of the three colours (including the hatching) isexplained in the text following the figure.


Debris flow -- D < 1 m D > 1 m

and and

v < 1 m/s v > 1 m/s

Static flooding h < 0.5 m 0.5 < h < 2 m h > 2 m

Dynamic flooding q < 0.5 m /s 0.5 < q < 2 m /s q > 2 m /s

Bank erosion t < 0.5 m 0.5 < t < 2 m t > 2 m

Process low intensity medium intensity high intensity

2 2 2

D = thickness of debris frontv = flow velocity (flood or debris flow)h = flow depthq = specific discharge (m /s/m) = h x vt = extent of lateral erosion

3

Figure 4.99 Flood hazard map in Switzerland based on the hazard levels


RED: high hazardThe red zone mainly designates a prohibition domain (area where development is prohibited).

BLUE: moderate hazardThe blue zone is mainly a regulation domain, in which severe damage can be reduced by means of appropriateprotective measures (area with restrictive regulations).

YELLOW: low hazardThe yellow zone is mainly an alerting domain (area where people are notified at possible hazard).

YELLOW-WHITE HATCHING: residual hazardLow probability of high intensity event occurrence can be designated by yellow-white hatching. The yellow-white hatched zone is mainly an alerting domain, highlighting a residual danger.

Figure 4.100 Flood depth map for a return period of 1/300 yr.

Figure 4.101 Map showing the flood hazard zones for the same region as in Figure 4.100

The direct interpretation of the hazard classes (red, blue, yellow, yellow-white) constitutes an excellent (legal)mechanism to directly implement the hazard maps into spatial planning and building regulations. In the red zone,all new urban development is prohibited, where as in the blue zone restrictive regulations are enforced. In theyellow zone there are principally no restrictions (except for highly sensitive infrastructure) but the residents aremade aware of the flood hazards.

The basis for the production of hazard maps is the so-called “intensity map”. The intensity (or magnitude) of aparticular process is delineated for each return period. In Figure 4.100 an example of a flood depth map is shownfor an event with a return period of 1/300 y with the flood depth indicated in steps of 0.25 m. Use is made of acolour ramp from light pale green (0 to 25 cm) slowly intensifying through orange to red for the greatest depth.In Figure 4.101 the flood hazards using the definition explained above is shown for the same region inSwitzerland.

There are very detailed documents available on the explanation of flood hazards and the use of the hazard zones.An interesting example is given in Figure 4.102 where the effect is shown of the implementation of floodmitigation measures (e.g. lowering of river bed, raising of dikes etc.) on the flood hazards.

In Switzerland the flood risk maps are not yet widely distributed. However, a qualitative risk can be depicted byoverlaying the hazard zones with the various land use classes (damage potential). In a first attempt this is done byjust using the topographic information (settlements, housing or industrial estates, transport infrastructure etc.). Animportant instrument is the so-called “Map of Safety Deficits” relating flood risks with protection objectives asshown in Figure 4.103.


Figure 4.102 Change in hazard level before and after implementation of flood mitigation measures


Figure 4.103 Map of safety deficit showing the degree of the lack of protection

Comment on the mapsSwitzerland has one of the most complete systems for the delineation of flood hazard and flood risk with andexcellent set of documents in German, French, Italian and English. Concepts, guidelines, and recommendations areavailable on the internet (environment-switzerland.ch / Documentation)


4.5 Great Britain

4.5.1 England & Wales

General informationIn England & Wales the Environment Agency has developed several mapping products to raise awareness of floodrisk and support decision making. Examples of these are shown as Figure 4.24 to Figure 4.28. All are available forpublic or professional use; some data is published on the Environment Agency’s internet site4.

The Flood Map is currently the Environment Agency’s main map to raise awareness of flood risk with the publicand our partner organisations, such as land use/spatial planning authorities, emergency planners, emergencyservices, developers and drainage authorities. It has been available on the internet since 2004, although an earlierversion was first published on the Internet in 2000. The Flood Map shows:• Flooding from rivers or the sea without defences – the natural flood plain area that could be affected in theevent of flooding from rivers and the sea.Two shaded areas are presented, which are aligned with the Flood Zones as defined by land use planning policyfor England:_ Areas that could be flooded either from rivers with an annual probability of flooding greater than 1% (1 in100) OR areas that could be flooded from the sea with an annual probability of flooding greater than 0.5%(1 in 200)

_ Areas other than covered by the above that would be flooded by an extreme flood with an annualprobability of 0.1% (1 in 1000) from rivers and the sea

• The location of flood defences – such as embankments and walls, and flood storage areas• Areas benefiting from these flood defences in a 1% fluvial flood or 0.5% coastal flood – where possible theareas that benefit from the flood defences are shown. However, not all areas that benefit from flood defencesare currently shown (Figure 4.24 is an example of this). Figure 4.25 shows how areas benefiting from defencesare shown where the information is available. There is ongoing work to increase the coverage of thisinformation.

On the internet the Flood Map is presented as a single layer in map form. Users search for their location of interestthrough a standard search tool by entering either a post code or a location name. The mapped output shown onthe internet site (default scale 1:20,000) is very similar to Figure 4.24, which has been shown at a scale of about1:45,000.The online Flood Map also has the facility to allow users to gain further information by opting to ‘learn more’ bypointing at a specific location within the map. This leads to data from the National Flood Risk Assessment, amapped data set which provides further qualitative information on the probability of flooding taking into accountthe location, type and condition of flood defences. This information on the actual (residual) probability of floodingis presented in three categories used by the insurance industry in the UK, as noted below:• Significant: the chance of flooding in any year is greater than 1.3% (1 in 75)• Moderate: the chance of flooding in any year is 1.3% (1 in 75) or less, but greater than 0.5% (1 in 200)• Low: the chance of flooding in any year is 0.5% (1 in 200) or less

Comments on the mapsA number of examples of mapped flood data are provided for England & Wales. Most relate to the city of Carlislein Cumbria to allow direct comparison of outputs, but a further example from Burton upon Trent (Figure 4.25) isshown to illustrate information not available on the Carlisle maps.

Figure 4.24 and Figure 4.25 both show extracts from the Flood Map. Flood extents ignoring the presence ofdefences, as described above, are shown. These extents are shaded in hues of blue, with the area of greaterprobability in the darker colour. The map also shows flood defences. Although these do not stand out well at thescale shown in the Atlas, they are clear on the internet version of the map shown at a scale of 1:20,000. Data onareas benefiting from defences is not available at all locations, but exists for all defences built since 1998. Further

4 http://www.environment-agency.gov.uk/



data is added to the Flood Map, as it becomes available, when modelling is updated. The Carlisle maps do notshow the areas that benefit from defences, although this is available for Burton upon Trent. The map layout isclear, with the topography shown on the background without too much detail. The internet site also provides anoverview map, to orientate the location within the national scale, although this is not shown on the example here.No ‘North’ indication is deemed necessary – it is customary that ‘North’ is at the top of the map in the UK. Thegrid with its coordinate references provides confirmation of this.

Figure 4.26 is a presentation of the assessment of flood probability bands for Carlisle as produced by the NationalFlood Risk Assessment. It maps the ‘Low’, ‘Moderate’ and ‘Significant’ flood probability bands as defined aboveand takes into account the reduction in probability as a result of flood defences. The underlying information usedto generate the map (the flood probabilities and depths) is also a step in the subsequent assessment of risk whencombined with depth/damage information. This banding is tailored more for commercial concerns as the insuranceindustry in the UK has a particular interest in the 1.3% limit. Whilst this data is not available in mapped format onthe internet, the information is available on the internet through the ‘Learn more’ option on the Flood Map.There may be discrepancies between this map and the areas benefiting from defences on the Flood Map. This isbecause the assessment used to develop the Flood Map does not take into account the presence or condition offlood defences, and so ignores the possibility of breach under different loading conditions. The areas benefitingfrom defences on the Flood Map may therefore show a greater area of ‘benefit’ when compared with the NationalFlood Risk Assessment results.

Figure 4.27 shows flood hazard rating data, with 7 bands of assessed hazard rating from 0 – 30 on a non-linearscale. The hazard rating (HR) is calculated as a function of velocity (v), depth (d) and a debris factor DF such thatHR = d x (v + 0.5) + DF. The hazard rating provides an assessment of the direct risk to life arising from thecombination of water depth and its velocity of flow, based on experiments, and includes a debris factor whichrecognises that debris-filled flowing water increases the danger to people. The map shown in this figure gives theabsolute values of this calculation. As this is a more specialized type of information, this map will be more useful tothe expert in flood risk than to the general public.

The formula on which this map is based is taken from the “Flood Risks to People – Phase II” report5. A simplifiedpresentation of the information for general use has been proposed in the report, as in the table below:

Figure 4.27 could have been produced using this banding rather than the banding shown. However, there areseveral uses for such maps and the needs of the user must be understood before deciding on the bandings. Forexample, the bandings in the table may be most useful for planning emergency response (evacuation routes, forexample) whereas the more detailed banding may be better for deciding where buildings and other infrastructureshould be located. This data has not been developed for the whole of England and Wales but will be producedwhere needed (using a risk based approach). The data is not available on the internet.

Figure 4.28 shows Social Flood Vulnerability. This map is very easy to read for the non-expert and gives a quickinsight into the vulnerability of either a person or property at different locations within extreme flood outline. The

d x (v + 0.5) Degree of Flood Hazard Description

<0.75 Low Caution“Flood zone with shallow flowing water or deep standing water”

0.75 – 1.25 Moderate Dangerous for some (i.e. children)“Danger: Flood zone with deep or fast flowing water”

1.25 – 2.5 Significant Dangerous for most people“Danger: flood zone with deep fast flowing water”

>2.5 Extreme Dangerous for all“Extreme danger: flood zone with deep fast flowing water”

5 http://sciencesearch.defra.gov.uk/Document.aspx?DocumentID=3646


number of people at risk from flooding, and their social status, is measured by “social vulnerability”. The FloodHazard Research Centre at Middlesex University developed a Social Flood Vulnerability Index (SFVI), based onthree social groups (long-term sick, single parents, the elderly) and four indicators of financial deprivation(unemployment, overcrowding, non-car ownership, non-home ownership). The SFVI can take a range of values,and these are divided into bands from 1 (very low vulnerability) to 5 (very high vulnerability). Each Output Area ofthe UK National Census has a SFVI band calculated, and the number of districts with each score in a flood risk areasuch as Carlisle is used to calculate the overall social vulnerability of that area. On the map provided for Carlisle,the ‘very low’ class is not present. This data is not available on the internet.

Figure 4.24 Flood extension map for the region of Carlisle

Figure 4.25 Example of flood map with indication of area benefiting from defence works

Figure 4.26 Flood hazard map of the region of Carlisle

Figure 4.27 Flood hazard rating map of the region of Carlisle

Figure 4.28 Social Flood Vulnerability map of the region of Carlisle

4.5.2 Scotland

In Scotland the organization SEPA looks after all aspects of flood control. Recently an interactive internet site hasbeen activated6 where for the whole of Scotland the expected flood extension is shown for a return period of1/200 years. Both flooding from rivers and the sea are incorporated. The information provided is very similar towhat is available for England & Wales, although they use a return period of 1/100 yr for river flooding and1/200 yr for flooding from the sea. An example is shown on Figure 4.29 for the city of Edinburgh.

Figure 4.29 Flood extension map for the city of Edinburgh from interactive internet site

Comments on the mapThe maps that can be produced with the interactive internet site have a very clear outline and are easy to read,partly because only a limited amount of information is presented (topography and expected flood extension byflooding from rivers and the sea). On the example shown in Figure 4.29 both types of flood origin are included.There is an option to show the flood defence works instead of the flood extension, but not both types ofinformation at the same time.


6 http://www.multimap.com/clients/places.cgi?client=sepa



7.2 Japan









7.3 Netherlands




exits



7.4 USA



flood maps-an excimap work

Documents

flood probability

flood extent

flood hazard maps

flood extension

flood mapping excimap

european flood risk

flood mapping development

level of flood risk