FLOOD ANALYSIS STUDY of INCHEON GYO CATCHMENT

2010

1August 20th, 2010CONTENTIntroduction

Data and Characteristics

Flood analysisMOUSESOBEKARC-SWAT

Conclusions and suggestions

2INCHEONLocated in the mid-west Korea peninsula near Yellow seaWith both international port and international airportThe third biggest city in KoreaPopulation : 2,730,000INTRODUCTION

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INTRODUCTION

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Reclamatation area used for industry and residenceTotal area : 34 kmMost of the present Incheon Gyo watershed has been sea before reclamatation was completed in 1985DATA AND CHARACTERISTICS

5Annual mean precipitation in Incheon in the last 30 years

64% of annual precipitationDATA AND CHARACTERISTICS

6Time (h)Rainfall (mm)4:00:00 AM05:00:00 AM06:00:00 AM127:00:00 AM178:00:00 AM559:00:00 AM7510:00:00 AM4511:00:00 AM812:00:00 PM91:00:00 PM82:00:00 PM73:00:00 PM54:00:00 PM15:00:00 PM06:00:00 PM0Flood event : 4th August 1997, 04 AM~06 PM

DATA AND CHARACTERISTICS

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PRECIPITATIONS4th August 1997

Rainfall intensity20 years50 years80 years100 yearsPRECIPITATIONS4th August 1997

Rainfall intensity20 years50 years80 years100 yearsDATA AND CHARACTERISTICS

8DATA AND CHARACTERISTICS

9Peak : 78.29 mm/hPeak : 96.67 mm/hPeak : 111.99 mm/hPeak : 107.07 mm/hDATA AND CHARACTERISTICS

10Gate Data

Tidal difference about 9 mWhen sea level up to EL.(+) 2.3 m(gate height) must be close during 6 hours twice of dayMain culvert outlet invertlevel is EL.(-) 0.09 mTo drain rainwater effected by reservoir water level (Backwater)

1D modelAnalysis of pipe network

Steps:1. Imput data to the software 2. Flooding analysis 3. Improvements on the pipe network to reduce flooding11

11MOUSE

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1250 years return period

FLOOD ANALYSIS

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1380 years return period

FLOOD ANALYSIS

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14100 years return period

FLOOD ANALYSIS

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FLOOD ANALYSISComparison between 20 and 50 years return period

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FLOOD ANALYSISComparison between 80 and 100 years return period

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17Reason of Flooding FLOOD ANALYSIS

80 years Comparison of change in pipe diameter and run-off coefficient 0.6

18IMPROVEMENTS TO REDUCE FLOODING

IMPROVEMENTS TO REDUCE FLOODING

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20IMPROVEMENTS TO REDUCE FLOODING

Connecting pipe system at one node Result: shows before and after

21IMPROVEMENTS TO REDUCE FLOODING1D vs 2D models

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Manholes (1D)1D can not represent flooding in depressed areas where there are no manholes. 1D can not represent flooding between structures or buildings, where there are no manholes1D models can study the pipes capacity. However:Moreover a 2D model can be very useful to distribute the manholes in a good way.232D Hydraulic and Hydrological study with SOBEKRain as a direct input of the model

Proposal: Study of Overland flooding caused by inadequate storm water drainage systems.

Advantages:A separate hydrological model is not required. The hydraulic model is used for rainfall runoff routing.

2324SOBEK characteristicsCoupled 1D-2D model.2D grid with square elements.Solve Saint-Venant equations

2425 2D model of terrain, buildings and structures Hydrological Study for sub-basin delimitation

High resolution of the modelHigh computational cost (time consuming)LimitationReduction of the Study area to a sub-basin.

ARC-SWAT

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Processing of theDEM interpolating:Manholes elevationContour

Digital Elevation Model (DEM): SWAT & SOBEK inputs

2627ARC-SWATArcGIS-ArcView extension. SWAT (Soil and Water Assessment Tool) is a river basin scale model developed to predict the impact of land management practices on water, sediment, and agriculture.

We use:Generation of the sub-basins with the DEM as a unique input.

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Selection of the sub-basin with:Reported flooding in 1997Downstream bond. Condition known No drainage system (manholes)Does not recieve water from other sub-basins

Flooded Areas (1997)Main flowdischargeManholesSub-basin selection

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Yellow seaFlooded Area in 1996Basin characteristics:AREA = 42 km2Soil use: URBANInfiltration will not be considered.

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Modeling of the 2D structures is important in order to evaluate flooding in the area.The structure of the railway is modifying the natural flow.Flooded area in 1996

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Modeling of the buildings Option 1: Elevation of the DEM overlapping the buildings shape file (resolution=5x5m)

3132 Option 2: Increase the roughness of buildings

Manning Coeff.0.03Building Manning Coeff.=0.1Other = 0.014

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33Comparison of the two methodsElevate buildingsIncrease roughness

Volume entering the buildingsnoYes

Modify flow directionYes

Yes

What is better?Secure sideIt is ok if one knows that water can enter the buildings34

34Sobek Interface

Input 2D and 1D schemesInput PrecipitationSimulation Settings35But after two days trying to run the model..

SOBEK didnt RUN!

We suppose that is a software problem with the server cause it didnt run even for the most simplified case in 1D.

The expected results will be similar than the video showed:

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Conclusions and improvementsDifferent software were used to generate results (Arc-GIS, MOUSE, SOBEK, SWAT)Several succesful simultaion were run in MOUSE for different return periods.Some pipe modifications were proposed to reduce flooding in some areas.No result was generated by SOBEK. However it is necessary to evaluate flooding with a 2D.Different approaches were worked out to reduce flooding in the future.

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38Thank you

Chart126.436.859.878.780.2138.9252.9218.4116.550.247.125.4

MonthMonthly precipitation (mm)

Sheet1Jan26.4Feb36.8Mar59.8Apr78.7May80.2Jun138.9Jul252.9Aug218.4Sep116.5Oct50.2Nov47.1Dec25.4

Sheet1

MonthMonthly precipitation (mm)

Sheet2

Sheet3