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APPLICATION OF GIS FOR APPLICATION OF GIS FOR FLOOD RISK ASSESSMENT: FLOOD RISK ASSESSMENT:

RATNAPURA TOWN, SRI LANKARATNAPURA TOWN, SRI LANKA

- CASE STUDY-

P. Liyanarachchi and Chandana Gunasena

Dept. of Geography, Dept. of Geography, University of University of RuhunaRuhuna, , Sri Lanka.Sri Lanka.

INTRODUCTION

Sri Lanka is lying between 6° and 10° N latitude and 79° and 81° E longitude. The island extends 432 km north and is 224 km wide.

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Study Area

SRI LANKA

RATNAPURA TOWN

RATNAPURA DISTRICT

RATNAPURA M.C.AREA

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Ratnapura M.C. area is located between 6° 41' and 6° 42'North latitudes and 80° 23' East to 80° 24'East longitudes.

The extent of M.C. limit is 2218.4 ha.

The contour height varies from 18m to 305m within the town limit.

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0

5

10

15

20

25

30

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

Years

Flo

od

lev

el (

m)

24.4m (critical flood)

21.3m (major flood)

20.1m (minor flood)

HISTORICAL FLOODS: Ratnapura town (1978-2003)

WARD EXTENT OF RATNAPURA M.C. AREA

2218.4TOTAL

137.2MUDDUWA15

138.1MUWAGAMA14

102.3DEWALEGAMA13

46.1POLUNGUPITIYA12

21.2FORT11

21.3BAZZAR10

18.2WARAKATOTA9

153.1BATUGEDERA8

167.5THIRIWANAKETIYA7

296.6ANGAMANA6

136.2GODIGAMUWA5

93.5POMPAKELE4

190.9WERALUPE3

415.3KOSPELAWINNA2

280.9HIDELLANA1

EXTENT (ha)NAME OF THE WARDNo.

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POPULATION DISTRIBUTION - 2002

2145822TOTAL

263519MUDDUWA15

435952MUWAGAMA14

333421DEWALEGAMA13

301378POLUNGUPITIYA12

841775FORT11

1082301BAZZAR10

1312390WARAKATOTA9

162512BATUGEDERA8

132230THIRIWANAKETIYA7

92755ANGAMANA6

375072GODIGAMUWA5

333051POMPAKELE4

173252WERALUPE3

83245KOSPELAWINNA2

112969HIDELLANA1

DENSITY PER (Ha)POPULATIONNAME OF THE WARDNo.

1002214.2Total7.9169Vacant & Cemetery12268.6Paddy

1.943.3Marshy16359.1Plantation

2.350.3Water bodies1.227.2Religious5.6125Forest1.227.2Parks & Playground0.48Industries

6128.1Transport3.578.5Public40885.3Residential244.6Commercial

%EXTENT (Ha)CATEGORY

LANDUSE OF RATNAPURA - 1998

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Determination of the flood inundation area according to the ward wise in the Ratnapuratown.

OBJECTIVESAssessing the risk of different flood scenarios for Ratnapura town due to flash floods.

To assessing the flood zonation based on the flood magnitude.

METHODOLOGYStored Stored datadata

Flood level Flood level at gauging at gauging stationstation

Digital Digital contour data contour data 1:5,0001:5,000

Digital Digital landuselanduse data data 1:5,0001:5,000

M.C. area M.C. area mapmap

Topographic Topographic maps maps 1:50,0001:50,000

Flood Flood frequency frequency analysisanalysis

DEMDEMRisk Risk analysisanalysis

Flood Flood scenario scenario mapsmaps

Return Return period and period and probabilityprobability

Flood Flood zonation zonation mapsmaps

Flood Flood inundation inundation area mapsarea maps

Flowchart –Flood Risk Assessment

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DATA COLECTIONDigital contour data (1:5000 )

Digital landuse maps (1:50,000 )

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Ward wise base map (1:5000 )

Flood flow data at the Ratnapuragauging station, 1977 - 2003

Ward wise socio-economic data of the U.C. area

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DATA ANALYSISFlood frequency analysis based on Gumble method

Return period

Probability

Created Digital Elevation Model (DEM)

Produced Flood scenario maps

Produced flood zonation maps

Assessed flood inundation area according to ward wise in the U.C. area

0.520032I

0110030H025028G

043026F

5.62025E

101023D

20522C

50220B

99118A

Probability %Return PeriodMax. Depth (m)

RESULTSAssessed return period and probability using Flood Frequency analysis through Gumble method.

Return period = N+1/ rN= Number of years r = Rank

P% = 100/rP= Probability r = Return period

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Flood magnitudes using annual flood data.

25 - 32Low risk zone

22 - 25Moderate risk zone

below 22High risk zone

Flood Magnitude (m)Flood Risk Zone

Digital Elevation Model (3D view)

Kalu ganga (river)

Ratnapuracity center

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Flood Scenario Maps

200 year flood scenario map200 year flood scenario map

49.61115.011150000Total

0.716.816790015

1.022.722720014

3.170.270170013

1.225.925920012

6.5145.1145080011

5.0111.9111920010

2.659.25918009

5.2116.811678008

3.987.68758007

1.124.62461006

1.226.32634005

3.476.07600004

6.9155.315534003

5.9131.913189002

2.044.74468001

%HectaresMetersWard No

200 year flood

Ratnapura M.C. area


48.41086.210862400Total

0.716.216240015

1.022.722720014

3.068.067990013

1.125.825800012

6.4142.8142760011

4.9110.3110260010

2.657.85784009

5.2116.411642008

3.886.48643007

1.124.32428006

1.226.12607005

3.374.87481004

6.9154.815479003

5.6126.812680002

1.533.03303001


100 year floodRatnapura M.C. Area

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43.4974.29741700Total

0.715.315250015

1.022.622550014

2.453.953900013

0.920.520520012

5.8129.9129860011

4.6103.2103190010

2.452.95285009

5.1114.211421008

3.578.67864007

1.123.82377006

1.124.72469005

3.067.06698004

6.6148.614862003

4.6102.510249002

0.716.71665001




40.3905.49053500Total

0.613.413430015

1.022.021950014

2.146.646560013

0.716.015970012

5.3118.8118810011

4.499.098950010

2.249.54951009

5.0112.611255008

3.374.77469007

1.022.52246006

1.023.22322005

2.761.86175004

6.4144.714467003

4.089.08898002

0.511.91185001

% hecHectaresMetersWard No


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38.9872.88727600Total

0.510.710720015

0.921.021000014

2.045.245190013

0.714.914900012

5.1114.5114530011

4.396.996850010

2.045.14514009

5.0111.511149008

3.373.27318007

0.920.72071006

0.920.62057005

2.659.05897004

6.4143.414343003

3.885.08500002

0.511.11108001




23.1519.45193500Total

0.11.21240015

0.510.810810014

0.920.820840013

0.36.56540012

2.965.765710011

3.271.971860010

0.36.5651009

2.965.26518008

2.351.05102007

0.613.61355006

0.613.41343005

2.147.24720004

5.4121.212117003

1.124.02401002

0.00.328001



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8.4189.21891700Total

0.00.015

0.37.77710014

0.11.61610013

0.00.9920012

0.511.211170011

0.512.212240010

0.00.440009

0.715.71574008

0.716.01603007

0.49.7966006

0.36.4643005

1.943.34325004

2.761.16114003

0.12.9287002

0.00.01




2.965.9659100Total

0.00.015

0.11.31310014

0.00.013

0.00.012

0.00.3320011

0.00.020010

0.00.09

0.11.8177008

0.13.1306007

0.25.5551006

0.24.3430005

0.818.11811004

1.431.53151003

0.00.02

0.00.01

% hecHectaresMeters


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Flood Zonation Maps

High risk zone mapHigh risk zone map

453.54Total

9.1714

18.3213

4.6612

58.8311

63.3410

1.39

56.388

42.227

11.746

11.075

46.314

113.783

16.422

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Area Ha.Ward No.

High Risk area

Ratnapura M.C. Area

Moderate risk zone mapModerate risk zone map

298.53Total

9.1415

9.9914

19.3713

6.9812

40.0411

18.9310

35.029

43.498

18.467

6.936

6.735

6.264

18.093

50.162

8.941

Area (Ha.)Ward No.

Moderate Risk area

Ratnapura M.C. Area

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Low risk zone mapLow risk zone map

272.12Total

6.115

1.7214

29.2713

12.2312

33.7211

17.2810

16.389

5.668

16.577

3.996

6.195

19.554

13.223

51.612

38.631

Area (Ha.)Ward No.

Low Risk area

Ratnapura M.C. Area

CONCLUTION

2.965.918.4189.22

23.1519.4538.9872.81040.3905.43043.4974.25048.41086.210049.61115.0200%

Inundated Area (Ha.)Return Period (years)

Flood risk assessment : inundated area according to Flood risk assessment : inundated area according to ward wise in the ward wise in the RatnapuraRatnapura town.town.

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1024.14Total272.12Low risk area298.48Moderate risk area453.54High risk areaHa.Zone

Flood risk assessment : inundated area according to Flood risk assessment : inundated area according to zone wise in the zone wise in the RatnapuraRatnapura town.town.

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