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

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