Flood hazard mapping four provinces of cambodia

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Presented in the ASEAN Cooperation on Utilization of Space Technology for Disaster Management Seminar, 11th Aug 2010 at Miracle Grand Convention Hotel, Thailand. Hosted by GISTDA

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Flood hazard mapping four provinces of cambodia

  1. 1. ‘Flood Hazard Mapping’ <br />Four Provinces of Cambodia <br />in the Mekong Basin<br />Arnob Bormudoi<br />Project Researcher<br />Geoinformatics Center<br />
  2. 2. Contents<br /><ul><li>Introduction
  3. 3. Statement of the Problem
  4. 4. Objectives
  5. 5. Limitations of the Study
  6. 6. Description of the study area
  7. 7. Data Used
  8. 8. Methodology
  9. 9. Results and Discussion
  10. 10. Conclusion and Recommendations</li></li></ul><li>Introduction<br />This study is about the simulation of a 1D flood model and utilization of its results for hazard mapping<br />
  11. 11. Problem Statement<br /><ul><li>Destruction of properties
  12. 12. Affects the agricultural practice
  13. 13. Loss of lives</li></li></ul><li>Study Area<br />Year 2000 <br />112 districts in 20 provinces were affected<br />300,000 out of 500,000 hectares of rice field destroyed (60%)<br />Year 2000 <br />186 dead, 606 sick over 460,000 families homeless<br />
  14. 14. Study Area<br />The Mekong<br />Flood Prone Areas<br />Ton Le Sap<br />Kampong Cham<br />Ton Le River<br />Phnom Penh<br />Kandal<br />Prey Veng<br />
  15. 15. Study Area<br />Position of Dykes<br />Highway No.5<br />Dartmouth flood observatory report (Year 2000 flood)http://www.dartmouth.edu/~floods/Archives<br />
  16. 16. Study Area<br />
  17. 17. Flood model<br />Q. Prediction of Flood ?<br />A. Flood Model..<br />Should produce fairlyaccurate results at less computing time<br />Should be cost effective<br />Hec-RAS<br />Hydrologic Engineering Centers River Analysis System<br />developed for the U.S. Army Corps of Engineers<br />It is a 1D model, Open source<br />
  18. 18. Objective<br />Estimate the flood depth and extent for the year 2000 flood in the four provinces Kampong Cham, Kandal, Prey Veng and Phnom Penh in Cambodia using Hec-RAS.<br />
  19. 19. The Climate<br />Monsoon Period from May~October<br />
  20. 20. Limitations<br />Hec-RAS a 1D model<br />Terrain is flat at d/s<br />Effect of the Ton Le Sap<br />
  21. 21. Data Used<br /><ul><li>Water level and the daily average discharge data (1991 to 2002) of the Mekong river in the gauge stations of Kampong Cham and Chroui Changvar.
  22. 22. The spot heights of the flood plains taken from the Data surveyed in 1960.
  23. 23. River bed cross section elevation data from Kampong Cham to Phnom Penh.
  24. 24. GPS surveyed data collected along the two river banks and the highway No.6 from Phnom Penh to Kampong Cham.
  25. 25. RADARSAT-1 image acquired on 23 Sep. and 25 Sep., 2000 as the base map of flood extent.
  26. 26. Landsat ETM of 3 Jan., 2005 used for preparing landuse map and delineating the Manning’s Roughness values for the flood plain.
  27. 27. Population data for these four provinces were obtained from the Seilaprogramme 2005 funded by UNDP.
  28. 28. Digitized river network, road network, administrative boundary and the location of schools.</li></li></ul><li>Filed Survey <br />
  29. 29. Methodology<br />Other Topographic Data<br />Landuse from Landsat ETM<br />Spot Heights of riverbed from existing data<br />Preparation Phase<br />TIN generation<br />Extraction of Manning’s Roughness coefficient from Landuse map<br />Model Execution Phase<br />Geometric Data Editing in<br />HEC-RAS<br />Model Simulation<br />For year 2000, September 11<br />(Flood Season)<br />Model Simulation<br />For year 2000, March 03<br />(Dry Season)<br />Hydrological Data<br />Verification & Result utilization<br />Socio Economic<br />and other ancillary Data<br />Flood Depth and Extent<br />As model output<br />Flood Extent <br />Verification<br />Model Result<br />SAR data as a<br />Base Map<br />Flood Depth<br />Verification<br />Hazard Mapping<br />Comparison with data from field<br />Model Result<br />
  30. 30. Results<br />Landsat 03January, 2005<br />
  31. 31. Results<br />Cross section at <br />Kampong Cham<br />(143 km)<br />Cross section at Chroui Changvar (36 km)<br />
  32. 32. Results<br />Flood Day (September 2000)<br />Dry Day (March 2000)<br />
  33. 33. Results<br />
  34. 34. Hazard Mapping part..<br />
  35. 35. Reclassification of Different Themes with Internal Weightage<br />Total Population per Commune<br />Population per Pixel<br />Weighted Landuse<br />Population per Commune x Weighted LU<br />Population per pixel =<br />Total weight <br />
  36. 36. Reclassification of Different Themes with Internal Weightage<br />
  37. 37. Assigning weightage based on AHP.<br />How to Give Weight to the Final Map Calculation?<br />Analytic Hierarchy Process (AHP) <br />Flood depth is 2 times as important as Population<br />Population is 3 times as important as Landuse<br />Flood depth is 4 times as important as Landuse<br />Final Hazard = 0.5584 x Flood Depth + 0.3196 x Pop per Pixel + 0.1220 x Landuse<br />
  38. 38. Hazard Map<br />Phnom Penh<br />
  39. 39. Comparison with the Base Data<br />Another Limitation<br />
  40. 40. Comparison of Depth<br />Minimum difference (Point Number 3 at Kampong Cham 0.05m )<br />Maximum Difference (Point Number 15 at Phnom Penh 5.2m )<br />
  41. 41. Results<br />Areas in each Province under Flood<br />Flooded Areas under each Depth Class <br />Highest area under depth of (3.5-6.5)m<br />Lowest Area under depth of (1.5-2.5)m<br />Kandal Province highest affected <br />Phnom Penh least affected<br />Maximum depth Kampong Cham<br />Minimum depth Phnom Penh<br />
  42. 42. Conclusion<br /><ul><li>Hec-RAS output of the flood extent by and large closely agreed</li></ul> with the base map of the study area.<br /><ul><li>Hazard analysis showed that maximum area under flood was</li></ul> between 3.5 to 6.5 meters.<br /><ul><li>Most of the areas affected by the flood was agricultural areas.
  43. 43. This approach can be extended to the other parts of the basin.</li></li></ul><li>Recommendation<br /><ul><li>For a more accurate model output, extensive surveys in the flood plains have to be carried out and recent sounding data of the riverbed will be useful.
  44. 44. Hydrological data for more than 25 years will be useful for flood frequency analysis.
  45. 45. Taking into consideration the uniqueness of this area the model would predict more accurate results if the effects of the Tonle Sap lake, Tonle and the Basak rivers are considered.</li></li></ul><li>Thank You..<br />

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