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T7: Flood Risk Assessment Using GIS Tools

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Flood Risk Assessment Using GIS Tools, By Dr. Omar Elbadawy, CEDARE, Land and Water Days in Near East & North Africa, 15-18 December 2013, Amman, Jordan

Flood Risk Assessment Using GIS Tools, By Dr. Omar Elbadawy, CEDARE, Land and Water Days in Near East & North Africa, 15-18 December 2013, Amman, Jordan

Published in: Education, Technology, Business

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  • 1. Land Resources Management Near East & North Africa Flood Risk Assessment Using GIS Tools
  • 2. Flow Diagram Processing Input Construct DEM Delineate watersheds Extract Stream network Calculate Watershed Characteristics Output Risk Matrix Vulnerability map GIUH Runoff Hydrograph 14000.00 60000.00 12000.00 10000.00 8000.00 6000.00 4000.00 50000.00 S-curves are lagged by 1 hour and the difference is found. 1-hour unit hydrograph resulting from lagging Scurves and multiplying the difference by 6. 40000.00 30000.00 20000.00 10000.00 2000.00 0.00 0.00 Time (hrs.) Flow (cfs) SCS Unit Hydrograph Flow (cfs/inch) Rainfall module
  • 3. Contours
  • 4. Elevation and constructing of DEM
  • 5. Flow Direction 32 64 128 16 8 1 4 2
  • 6. Flow Accumulation 32 64 128 16 8 1 4 2
  • 7. Delineating the watersheds and Stream Networks
  • 8. Delineating the watersheds and Stream Networks
  • 9. Selected parameters          Area (A) weighted mean of bifurcation ratio (WMRB) stream frequency (F) drainage density (D) shape index (Ish) slope index (Sl) relief ratio (Rr) ruggedness number (Rn) texture ratio (Rt).
  • 10. Watershed Factors  Watershed size - runoff volumes and rates increase with watershed size
  • 11. Watershed Factors  Watershed shape - runoff rates tend to be lower for long narrow watersheds than for compact water sheds having the same area Long “time of concentration” Short “time of concentration”
  • 12.  Drainage Density and Stream Frequency D= 1 A   N  L  =1  F=  N  =1 A
  • 13. Risk value  4 * ( x  xmin ) 1 ( xmax  xmin ) Risk Calculation ( x  xmin ) Risk value  4 * 1 ( xmax  xmin ) x = the parameter value xmin = the minimum value of the parameter according to all studied basins xmax = the maximum value of the parameter according to all studied basins
  • 14. Basin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 A WMRb 1 4 5 5 3 4 2 4 1 4 1 4 1 5 1 4 1 5 1 5 1 1 1 5 1 2 1 5 1 4 1 5 1 3 1 5 1 4 1 3 1 4 1 4 F 2 2 2 2 3 3 1 3 3 2 1 3 1 5 4 4 3 4 1 2 2 3 D Ish 2 3 3 3 3 2 3 2 1 3 2 2 3 2 2 2 3 4 3 3 1 1 3 4 2 1 3 2 3 2 3 3 4 2 3 2 5 1 3 1 3 2 4 5 Sl 3 1 1 1 1 1 2 1 2 3 3 3 3 3 4 5 5 5 2 2 3 2 Rr 4 1 1 1 1 1 2 1 2 3 3 4 3 3 4 5 4 5 4 1 3 3 Rn 4 5 3 4 1 1 3 1 2 3 3 2 3 2 3 3 4 3 3 1 4 5 Rt 1 5 3 3 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 Risk Degree 3 5 4 3 2 2 3 2 3 2 1 3 2 3 3 3 3 3 2 1 3 4
  • 15. N W E S 20 0 20 40 Kilometers Risk Fig (6.6) Risk map 1 2 3 4 5 Suiez can al Nile
  • 16. Rainfall Analysis
  • 17. Used Events   100 year maximum daily rainfall 49 mm for 3 hours period event. 50 year maximum daily rainfall 38 mm for 1 hour
  • 18. 120 D DISCHARGE, q 90 tp 60 qp 30 tb 0 0 1 2 3 TIME, t 4 5 6
  • 19. Basin 1 Area 19.375 LΩ 6.01 RB 5.00 RL 3.267 RA 6.223 SΩ 12.35 v 7.54 N 3.013489 K 0.097476 km2 Km % m/s
  • 20. Basin 1 - Event 1 20 18 16 12 10 8 6 4 2 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Tim e, hr Basin 1 - Event 2 30 25 20 Q, m3/s Q, m3/s 14 15 10 5 0 0 0.5 1 1.5 2 2.5 Tim e, hr 3 3.5 4 4.5 5
  • 21. Basin 2 Area 1761.345 km2 LΩ 63.81 Km RB 4.62 RL 2.649 RA 5.059 SΩ 1.59 % v 2.71 m/s N 3.279033 K 2.998812
  • 22. Basin 2 - Event 1 450 400 350 250 200 150 100 50 0 0 10 20 30 40 50 60 Tim e, hr Basin 2 - Event 2 250 200 Q, m3/s Q, m3/s 300 150 100 50 0 0 10 20 30 Tim e, hr 40 50 60
  • 23. Event 1 Qp Tp Basin (m3/s) 1 18.40 2 421.46 3 215.55 4 150.36 5 5.22 6 17.92 7 87.14 8 6.03 9 14.61 10 22.89 11 9.17 12 3.28 13 7.29 14 3.03 15 7.98 16 7.05 17 8.01 18 8.48 19 2.85 20 3.20 21 35.10 22 89.33 (hr) Event 2 Qp Tp 3 (m /s) 0.8 28.23 8.0 217.40 7.0 111.76 6.0 78.90 0.6 7.93 2.4 21.49 3.4 58.18 1.0 9.47 1.6 19.33 2.2 27.13 0.8 16.41 0.6 6.66 0.6 13.28 1.0 4.83 0.6 2.82 1.0 11.21 1.0 12.42 1.4 12.21 1.0 4.51 1.2 5.00 2.6 38.94 3.4 57.59 (hr) 1.0 7.0 6.0 5.0 0.6 1.2 2.0 0.9 1.0 1.2 0.7 0.5 0.9 1.0 0.6 1.0 1.0 1.0 1.0 1.0 1.3 2.0
  • 24. Event 1 Qp Tp Basin (m3/s) 1 18.40 2 421.46 3 215.55 4 150.36 5 5.22 6 17.92 7 87.14 8 6.03 9 14.61 10 22.89 11 9.17 20 12 3.28 13 7.29 14 3.03 15 (6.6)7.98 Fig Risk 16 map 7.05 17 8.01 18 8.48 19 2.85 20 3.20 21 35.10 22 89.33 (hr) Event 2 Qp Tp 3 (m /s) 0.8 28.23 8.0 217.40 7.0 111.76 6.0 78.90 0.6 7.93 2.4 21.49 3.4 58.18 1.0 9.47 1.6 19.33 2.2 27.13 0.8 16.41 0 0.6 6.66 0.6 13.28 1.0 4.83 0.6 2.82 1.0 11.21 1.0 12.42 1.4 12.21 1.0 4.51 1.2 5.00 2.6 38.94 3.4 57.59 (hr) 1.0 7.0 6.0 5.0 0.6 1.2 2.0 0.9 1.0 1.2 0.7 0.5 0.9 1.0 0.6 1.0 1.0 1.0 1.0 1.0 1.3 2.0 N W E S 2 20 20 40 Kilometers 0 20 40 Kilometers Risk Fig (6.6) Risk map 1 Risk 1 2 2 3 3 4 5 4 Suiez can al Nile 5 Suiez can al Nile
  • 25. Event 1 Qp Tp Basin (m3/s) 1 18.40 2 421.46 3 215.55 4 150.36 5 5.22 6 17.92 7 87.14 8 6.03 9 14.61 10 22.89 11 9.17 20 12 3.28 13 7.29 14 3.03 Fig 15 (6.6)7.98 Risk 16 map 7.05 17 8.01 18 8.48 19 2.85 20 3.20 21 35.10 22 89.33 (hr) Event 2 Qp Tp 3 (m /s) 0.8 28.23 8.0 217.40 7.0 111.76 6.0 78.90 0.6 7.93 2.4 21.49 3.4 58.18 1.0 9.47 1.6 19.33 2.2 27.13 0.8 16.41 0 0.6 6.66 0.6 13.28 1.0 4.83 0.6 2.82 1.0 11.21 1.0 12.42 1.4 12.21 1.0 4.51 1.2 4.02 2.6 38.94 3.4 57.59 (hr) 1.0 7.0 6.0 5.0 0.6 1.2 2.0 0.9 1.0 1.2 0.7 0.5 0.9 1.0 0.6 1.0 1.0 1.0 1.0 1.0 1.3 2.0 N W E S 20 20 20 40 Kilometers 0 20 40 Kilometers Risk Fig (6.6) Risk map 1 Risk 1 2 2 3 3 4 5 4 Suiez can al Nile 5 Suiez can al Nile
  • 26. Conclusions  The proposed methodology proved to be suitable for the arid wadi system especially when detailed data is not available  The selected geomorphological parameters for risk assessment are well matched with the results from estimated runoff hydrograph when both peak discharge and time to peak are considered  GIS has proved to be an easy and efficient tool for watersheds flood risk assessment.  The risk classification presented provides a prioritization skim for flood control and flood protection programmes.  The study presents an integrated approach for flood risk assessment for AlSokhna area, and should be reflected in development plans for the area
  • 27. Thank You
  • 28. Geomorphologic • Uses stream network topology and probability concepts • Law of Stream Numbers range: 3-5 • Law of Stream Lengths range: 1.5-3.5 • Law of Stream Areas range:3-6 N 1  RB N RBu ( N u  N u 1 ) RBu 1 WMRb  N L  RL L 1 A  RA A 1 29
  • 29.  Relief and Slope Ratios R Rr  LB E Sl  0.75Vl
  • 30. Instantaneous Unit Hydrogaph GIUH IUH 0.55 0.44 L  R B    tp=   RA  qp = 1.31 L R - 0.38 L qp= 0.871 i 1 ( ) hours .4 2.5  0.43 L R i= L 1.5 i r A R L   ir is the intensity of effective rainfall in cm/h AΩ is the area of the watershed in km2 αΩ the kinematic parameter for the stream of highest order 1/2 SΩ is the average slope of the highest order stream nΩ is the average Manning roughness coefficient of Ω bΩ is the average width of the highest order stream, in m S =  2/3 n b
  • 31. Risk Assessment Parameters Watershed characteristics Area Perimeter Basin length Valley length Length of overland flow Ruggedness number Texture ratio Stream morphology Stream frequency Drainage density Stream order Sum of stream number Sum of stream length RB RL RA WMRb Topographic and shape Slope index Circularity ratio Elongation ratio Relief Internal relief Relief ratio Shape index sinuosity

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