flood risk assessment and modelling a k lohani

7/31/2019 Flood Risk Assessment and Modelling a K Lohani

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BRIEF OVERVIEW ON FLOODRISK ASSESSMENT AND

MODELLING

Dr. A.K. LohaniScientist E2

NATIONAL INSTITUTE OF HYDROLOGYROORKEE-247667

[email protected]

[email protected]

[email protected]
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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Outline of Presentation

What is Flood Risk Assessment?

Types of Floods

Definitions of terms related to flood riskmapping and flood plain zoning,

Approaches to flood hazard/risk

mapping, Methods & Models for flood hazard/risk

mapping and data requirement.

Data requirement & Software


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TYPES OF FLOOD Flash floods

Single event floods

Multiple event

flooding Seasonal floods

Dam break floods

GLOF

Floods due to

drainage congestion


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Definitions of Terms

Flood inundation map

Flood hazard map

Flood risk zone map

Flood plain zoning map


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Flood inundation map

Inundation map during a flood eventwhen the flood water in the riverovertops its banks and leads to the

flooding of adjoining areas or floodplains.


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Flood hazard map

A flood hazard map provides information

about the return period associated with the

areal extent of inundation for a reach of a

river.


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Flood risk zone map

A flood risk zone map providesinformation about the risk associatedwith the damages caused or losses

resulting from a flood event in aparticular area or flood risk zone.


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Flood plain zoning map

A flood plain zoning map categorizesvarious zones based on administrativelegislations for planning and

development of the flood plains forvarious purposes such as agriculturalactivities, play fields, industrial areas

and residential areas etc.


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Approaches to flood hazard &flood risk mapping

Geomorphological approach

Historical approach Damage approach

Remote sensing data based approach

Hydrological-hydraulic approach


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Geomorphological approach

For estimating the qualitative floodhazard.

Maps based on this approach may notbe reliable if embankments are presentand raised markedly.

More suited to relatively uncontrolledor virgin natural river basins.


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Historical approach

Major floods marks may appear assilt deposits on sloping river banksand on trees, erosion traces on banks

and around trees, and discolorationof structures. Information obtained from interviews/

literature and compared with the

elevations of the high-water marks.


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Historical approach

Soil types study to determine thehistorical floodplain.

This approach cannot take intoconsideration the effects of futureurbanization of a watershed on therunoff and inundation.

It is impossible to directly determinethe inundation areas for a given rainfallevent if sufficient historical flood dataare not available.

Historical inundation data are best

used for calibrating the inundationmodel.


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Remote sensing data basedapproach

It can provide information on floodinundated areas for differentmagnitudes of floods so that the extentof flooding can be related to the floodmagnitude or flood stages of the river.

Inundation extent for specific flood

return periods may also be estimated.


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The method basically consists of

Frequency analysis of flood stage ofpartial duration series and estimation of

stage for various return period. Preparation of flood inundation map from

satellite data corresponding to various

stages used for frequency analysis. Development of relationship between

stage and inundation area.


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Frequency Analysis

Identify some of the highest stage values ofthe observed river flow at the gauging site

each year for a period of 10 to 15 years. Form a partial duration series of about 30

stage values for the gauging site carry out

frequency analysis. Using the frequency relationship

developed; estimate the values of thestages corresponding to various return

periods.


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Inundation mapping

The flood inundation maps are prepared

using digital image processing softwarelike ERRDAS, ILWIS etc.


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Stage & area relationship

Develop the relationships between stages

of the partial duration series and eachcomponent of the flooded area.


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Prediction of flood hazard area for anystage of river flow

Using the developed relationships theflooded areas corresponding to any stagemay be computed.

These flooded area may be marked on the

toposheets by following the patterns of theflooded area corresponding to theobserved stages.


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Hydrological-hydraulicapproach

It utilizes the hydrological and hydraulicmodels to simulate quantitatively the depth,area and duration of inundation.

Maps based on this approach not only showinundation profile but may also be used toevaluate the effects of flood controlprograms such as river channel

improvements, and flood water detentionreservoirs, as well as urbanization of thewatershed etc.

H d l i l h d li


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Hydrological-hydraulicapproach

It is a GIS based approach for the developmentof a terrain model based on stream channelrepresentation using some hydraulic model.

Floodplain and channel geometry is delineated

in a GIS like ArcView. All the model parameter for hydraulic routing of

the floods are also defined/ computed in thesame GIS environment.

Calculate water surface profiles for the floodsof different return periods.

The results of the model are exported to GIS forthe floodplain delineation and mapping


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Data Requirement for Flood RiskAssessment & Modelling

DEM of the floodplain

Floodplain and channel geometry: rivercenterline, banks, river cross sections

Mannings roughness coefficients of riverbed and flood plain

Remote Sensing Data, Land use

Historical gauge-discharge data

Historical inundation data

Administrative maps


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PUBLIC DOMAIN & COMMERCIALSOFTWARE

ERRDAS

ILWIS

ArcView

ArcGIS

Mike 11

Mike 21

Mike Flood

HEC-RAS

HEC HMS

Software for Flood Risk Assessment &Modelling


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MIKE 11 Flood risk analysis and mapping

Design of flood alleviation systems Real-time flood forecasting

Real-time water quality forecasting andpollutant tracking

Hydraulic analysis/design of structuresincluding bridges

Drainage and irrigation studies

Optimization of river and reservoir operations

Dam break analysis

Water quality issues

Integrated groundwater and surface wateranalysis


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MIKE 21

a professionalengineeringsoftware packagefor the simulationof flows, waves,sediments and

ecology in rivers,lakes, estuaries,bays, coastal areas

and seas


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MIKE 21..

a professional engineering softwarepackage containing a comprehensivemodeling system for 2D free-surface

flows.

It is applicable to the simulation ofhydraulic and related phenomena in

lakes, estuaries, bays, coastal areasand seas where stratification can beneglected.


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MIKE FLOOD - river andfloodplain hydraulics

An integrated tool for detailed floodplainstudies.

Combines the two numerical hydrodynamicmodels MIKE 11 (1-D) and MIKE 21 (2-D) witha unified user interface

Detailed spatial modelling where needed,plus the speed of 1-D calculations where

appropriate. Ideal for many types of analyses such as

flooding, storm surge, dam break,embankment failure, and more.


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Software of HydrologicEngineering Center (HEC)

HEC-GeoRAS

HEC-HMS


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HEC-GeoRAS A set of procedures, tools, and utilities for

processing geospatial data in ArcGIS using a

graphical user interface (GUI). The interface allows the preparation of geometric

data for import into HEC-RAS and processessimulation results exported from HEC-RAS.

Water surface profile data and velocity dataexported from HEC-RAS simulations may beprocessed by HEC-GeoRAS for GIS analysis forfloodplain mapping, flood damage computations,ecosystem restoration, and flood warningresponse and preparedness.


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HEC-HMS

Designed to simulate the precipitation-runoff

processes of watershed systems.

Applicable in solving the widest possible rangeof problems which includes large river basin

water supply and flood hydrology, and smallurban or natural watershed runoff.

Output used directly or in conjunction withother software for studies of water availability,

urban drainage, flow forecasting, futureurbanization impact, reservoir spillway design,flood damage reduction, floodplain regulation,and systems operation.


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THANK YOU

flood risk assessment and modelling a k lohani

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