Flood Management Systems

Edward Walsh

DT117/4

C06515036

Sonya Daly

Flood Management Systems Edward Walsh

Table of Contents

WHAT IS FLOODING?..................................................................................................................... 4

FLOOD POLICY IN IRELAND......................................................................................................... 4

FLOOD RISK ASSESSMENT........................................................................................................... 5

FLOOD RISK MANAGEMENT PLANS.......................................................................................... 6

SUSTAINABLE URBAN DRAINAGE SYSTEMS (SUDS)...........................................................7

REFERENCES.................................................................................................................................. 10

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Table of Figures

FIGURE 1: TRENDS IN PRECIPITATION IN IRELAND................................................................................................4

FIGURE 2: SOURCES, PATHWAYS AND RECEPTORS OF FLOODING........................................................................6

FIGURE 3: SWALE AND FILTER STRIP.....................................................................................................................8

FIGURE 4: FILTER DRAIN AND PERMEABLE SURFACE............................................................................................8

FIGURE 5: INFILTRATION BASIN AND SOAKWAY...................................................................................................9

FIGURE 6: DETENTION POND.................................................................................................................................9

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What is Flooding?Flooding is a natural process that can occur at any time in any location and in inevitable part

of life in Ireland today. They are mainly caused by overflowing of seas and rivers but

prolonged and intense rainfall can cause sewer flooding, overland flooding and groundwater

flooding. Flooding has become a more frequent event over the last decade in Ireland causing

devastation to people’s properties that are at risk. This increase is primarily due the effect of

climate change. Climate change will affect the levels of precipitation in Ireland with an

increased hydrological cycle. Changes in weather patterns will occur along with the amounts

and characteristics of precipitation.

Figure 1: Trends in Precipitation in Ireland

While we cannot prevent flooding from occurring, we can prepare for it and reduce resulting

damage and suffering. It is important that a reduction in these future potential flood risks be

achieved by incorporating the assessment of flood risk into the planning phase.

Flood Policy in Ireland

In September 2008, the Department of Environment, Heritage and Local Government and the

Department of Finance with responsibility for the OPW published new planning guidelines

on The Planning System and Flood Risk Management. This was aimed at ensuring a more

consistent, rigorous and systematic approach to fully incorporate flood risk assessment and

management into the planning system.

These new guidelines are focused on providing for the wide-ranging consideration of flood

risk in regional, development and local area plans as well as assessing planning permission

applications in line with the proper principles and sustainable development. They also take

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account of environmental considerations including the need to manage the inevitable impacts

of climate change, biodiversity etc., and the EU Directives on Flooding and the Water

Framework Directive which established the concept of river basin management.

These guidelines will require the planning system at national, regional and local levels to

follow the following requirements:-

Building and development is to be evaded in areas with a risk to flooding unless the

risk can be managed or reduced to an appropriate level without increasing flood risk

elsewhere; and where are sustainable grounds that validate suitable development.

It is of practice to adopt a sequential approach to flood risk management and plan

developments away from areas that have been identified as flood prone through flood

risk assessment.

Flood risk assessment should be included when making decisions in the planning

process.

Flood Risk Assessment

To undertake a flood risk assessment, it is necessary to understand the source of the

water, how and where it flows and the hazards that will occur to people and assests

affected by it.

Figure 2: Sources, pathways and receptors of flooding

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The stages of assessment include:

1. Screening Assessment- identifies if there are any flooding or surface water issues

with the development that may require further investigation.

2. Scoping Assessment- identify the sources of flooding that will affect the site and

scope of the extent of the risk, the potential impacts on the development and the

possible mitigation measures.

3. Appropriate Risk Assessment- assessment of flood risk issues in specific detail and

provide appraisal of the potential impact on flooding elsewhere and effectiveness of

any propped mitigation measures.

Flood Risk Management Plans

The aim of Flood Risk Management is to minimise the risks arising from flooding to people,

property and the environment. After the assessment phase has been completed, the next stage

is to design a flood risk management system. The following actions should be taking into

consideration when devising a flood risk management system:-

Flood hazard and potential risk should be identified and considered at the earliest

stage in the planning process.

Risks should be reduced or eliminated by developing areas with little or no flood risk.

Development should only be granted in areas of flooding risk where there are no

alternative, lower risk sites available in the area.

Future effects of climate change and coastal erosion should only be taken into

consideration when designing developments in areas of high risk. A precautionary

approach should be employed so that future occupants are no subject to unacceptable

risks.

Thorough assessments of flood risks should be undertaken before a review of

development plans to ensure compliance with the guidelines, to ensure that land is not

zoned or developments granted permission before the risk is fully known.

Land which will be required for future sustainable flood risk management should be

identified on local area plans to avoid development in these areas.

Flood risk to, and arising from, new development should be managed through

location, layout and design incorporating sustainable drainage systems. E.g. SUDS.

Strategic Environmental Assessment (SEA) of Regional Planning Guidelines,

Development and Local Area Plans should include flood risk as one of the key

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environmental criteria against which such plans are assessed where flood risk has

been identified.

The SEA planning guidelines will be updated to reflect the need for flood risk to be identified,

assessed and managed.

Sustainable Urban Drainage Systems (SUDS)Sustainable Urban Drainage Systems (SUDS) is an approach to drainage that recognises the

wider consequences of urban development. In built-up areas, rainfall has little or no natural

drainage route, and so must rely heavily on drainage infrastructure. This concept considers

the long term environmental factors in decisions about drainage. They can consist of one or

more structures which combined with good management of a site, prevent flooding and

pollution. Its main objective is to minimize storm water runoff and to collect and treat this

water as close to the source as possible.

The four main methods of control are:-

1. Filter strips and swales

Figure 3: Swale and Filter Strip

2. Filter drains and permeable surfaces.

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Figure 4: Filter drain and Permeable Surface

3. Infiltration devices.

Figure 5: Infiltration Basin and Soakway

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4. Basins and ponds.

Figure 6: Detention Pond

References

Wavin- What is SUDS (n.d.) [Online] Available:

http://ie.wavin.com/master/master.jsp?FOLDER%3C

%3Efolder_id=2534374305437765&middleTemplateName=oc_middle_research_sub

_sub (Accessed on 23rd March 2010)

Department of Environment, Heritage and Local Government- The Planning System

and Flood Management Guidelines (2008)

Department of Environment, Heritage and Local Government (2007) [Online]

Available:

http://www.environ.ie/en/DevelopmentandHousing/PlanningDevelopment/

NationalSpatialStrategy/News/MainBody,18440,en.htm (Accessed on 23rd March

2010)

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