flood risk assessment and modelling a k lohani
TRANSCRIPT
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BRIEF OVERVIEW ON FLOODRISK ASSESSMENT AND
MODELLING
Dr. A.K. LohaniScientist E2
NATIONAL INSTITUTE OF HYDROLOGYROORKEE-247667
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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Remote sensing data basedapproach
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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Remote sensing data basedapproach
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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Remote sensing data basedapproach
Inundation mapping
The flood inundation maps are prepared
using digital image processing softwarelike ERRDAS, ILWIS etc.
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Remote sensing data basedapproach
Stage & area relationship
Develop the relationships between stages
of the partial duration series and eachcomponent of the flooded area.
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Remote sensing data basedapproach
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