4 th Joint Project Team Meeting for Sentinel Asia 2011

Transcription

1 A Revisit on the Structural Flood Mitigation Measure with the Application of Remote Sensing and GIS in Gin River Basin, Sri Lanka 4 th Joint Project Team Meeting for Sentinel Asia 2011 Geoinformatics Center Asian Institute of Technology

2 Participating Agencies Irrigation Department, Sri Lanka S.M Premasiri Survey Department, Sri Lanka B.C.P. Bogahawathta

3 Introduction/Background/Significance of the project 1.Sri Lanka is an Island in southeast of India Sq Km Areal extent Central part of the country is the hilly area. 3. Highest Elevation m msl

4 Four Seasons First Inter-Monsoon (March April) Average Rainfall =268.0 mm (14%) Almost all parts of the island receives rain in excess of 250 mm South West Monsoon (May to Sep.) Average rainfall = mm (30%) Varies between 100 mm to over 3000 mm

5 Second Inter-Monsoon (Oct. to Nov.) North East Monsoon (Dec. to Feb.) Average Rainfall =558.0 mm (30%) Almost every part of the island receives in excess of mm SW slopes of the hills mm mm Average = mm (26%) Higher Rainfall in the Eastern Slopes

6 Classification of Climate Zones Annual rainfall varies between mm to mm with an Average = mm Dry Zone RF <1750 mm Intermediate Zone = 1750<RF<2500 Wet Zone RF > 2500 mm Gin Ganga Basin

7 Recorded maximum rainfall intensities for - 24 hours in Sri Lanka Highest mm on 15 th Nedunkerny December 1897 at mm on 16 th May 1940 at Rassagala Balangoda mm on 4 th June in Colombo mm on 17 th May at Wille Group - Deniyaya 440 mm on 10 th November in Colombo (Source:- Meteorology Department Sri Lanka)

8 Introduction Consequence: Frequent Flooding 1. Kalu River 2. Kelani River 3. Gin River 4. Nilwala River 5. Mahaweli River

9 Study Area River Basin Number = 9 Basin Area = 932 km 2 Upper Elevation = 1120 m Length of the River = 119 km Region = Wet Zone Average Annual Rainfall =3200 mm Runoff / Rainfall Ratio = 58%

10 Study Area Flood regulation Bunds 74 Total Length m

11 Objectives To produce a DEM of the Gin river basin replicating the natural and man-made topographical features To establish a flood routing model for the Gin River basin To analyze the flood hazard in Gin River basin To evaluate the adequacy of the existing flood regulation system in support of maintaining/enhancing the flood mitigation measure/s.

12 Methodology Data Collection

13 Methodology.. 1 Field Visit 2 collect point measurements on flood depth and flood area extent 3 collect ground-truth data on land cover land use carry out a river cross sections survey

14 4 Field Visit

15 Methodology DEM Generation Flood Bund 1. Update the Contour Map Using Bund cross sections Elevation Modeling of flood protection bund

16 Methodology DEM Generation Elevation Modeling of flood protection bund 2. Develop tools to Update the existing DEM

17 Methodology DEM Generation Elevation Modeling of flood protection bund 2. Develop tools to Update the existing DEM

18 Methodology DEM Generation This Model Creates a Smooth DEM Using Spot Heights and Contours

19 Methodology DEM Generation Incorporating the river bathymetry

20 Methodology The one dimensional steady flow module of HEC-RAS model was used for the flood routing. The requisite geo-spatial modeling of the flood plain was carried out by implementing HEC-GeoRAS module in ArcGIS environment. Updated DEM Land Use Map River Discharge Hec Geo RAS Output of Hec Geo RAS Hec RAS Model Calibration Flood Routing Maps of different return periods

21 Methodology HEC - RAS Model Establishment and Calibration With reference to year 2003 flood event 0.75m

22 Methodology Situation Analysis using ALOS/PALSAR Although the flood bunds route the upstream discharge, rainfall in the lower reach has been experienced to cause flooding. Such a situation, with the availability of ALOS data sets, was analyzed as contributory to flood mitigation measures. ALOS/PALSAR data of 2008 July flood event as well as that of a dry date were used for the purpose

23 Methodology.. Frequency Analysis Observed Peaks Obwerved Flood Peaks - Gin Ganga at Tawalama (37 Years - from 1973/74 to 2009/10) 1876 m3/sec 5 am on18th May Mean Peak Discharge = 452 m3/sec (with Peak 2003) Diischarge in m 3 /sec / / / / / / / /2009 Mean Peak Discharge = 413 m3/sec (without Peak 2003) Time in Water Years

24 Methodology.. Frequency Analysis Gumbel Linear Partition Return Period T ( years) Peak Flood Q ( m 3 /sec)

25 Results the 3 dimensional view of the DEM with the flood bunds and the river channel.

26 Results

27 Results

28 Results

29 Conclusions Remote sensing, GIS, and GPS together with flood modeling technique have successfully been applied to model existing flood routing system at the lower Gin basin in support of disaster preparedness and mitigation activities. A DEM replicating the natural and man-made features of the terrain has been produced with the ability to modify the heights of flood bunds as would be necessary for scenario modeling. Inundations due to the flooding event of year 2008 has been mapped successfully using ALOS/PALSAR derived remote sensing data Outcomes of this study would be very much useful in devising an effective and efficient flood mitigation and management strategy in the lower Gin basin.

30 Awareness Workshop At the Irrigation Department

31 Satellite Activation by Sentinel Asia Secretariat with cooperation of ADRC

32 Satellite Activation by Sentinel Asia Secretariat with Cooperation of ADRC

33 Acknowledgement Special thank The Japan Aerospace Exploration Agency (JAXA) for providing financial support and ALOS data through Mini-Projects. The Geoinformatics Centre of Asian Institute of Technology for providing educational and an excellent study environment. MOSTI NSC

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