1. Hydrologic Characteristics of Floods in Ganges-Brahmaputra- Meghna (GBM) Delta A.K.M. Saiful Islam Sujit Kumar Bala Institute of Water and Flood Management (IWFM) Bangladesh University of Engineer and Technology (BUET) International Symposium “Hazard Management for Sustainable Development” 29 th November, 2009, Kathmandu, Nepal

2. Outline of the Presentation  Main Causes of Floods in Bangladesh  Hydrologic Aspects of Past Major Floods  Flood Inundation Maps using MODIS images  Performance of Flood Control Works around Dhaka City.

3. The Ganges, Brahmaputra, and Meghna (GBM) River Basins 93% water comes outside of Bangladesh

4. River System and GBM Grid

6. TRMM Rainfall over GBM 3 hourly rainfall with spatial resolution 0.25 degree

7. Rainfall (May-Sep, 1998)

8. Rainfall (May-Sep, 2004)

9. Rainfall (May-Sep, 2007)

10. Normalized Monthly Rainfall

11. Monthly rainfall over GBM basin during July using TRMM 3-hourly data. Ganges Brahmaputra Meghna

12. Chronology of the entrance of 2007 Flood

13. Water Level Stations in Major Rivers

14. Height of Peak above DL 2007200419981988 Brahmaputra0.880.680.871.12 Ganges--0.940.62 Meghna0.691.531.081.41

15. Duration of flood above DL 2007200419981988 Brahmaputra21156716 Ganges002623 Meghna37386775

16. Floods in Major Rivers 19881998 20042007

17. Brahmaputra at Bahdurabad

18. Ganges at Hardinge Bridge

19. Meghna at Bhairab Bazar

20. Flood Inundation Map based on MODIS Satellite Data

21. Land Use Classifications

22. MODIS derived Indices Where, Band 1: Red, Band 2: NIR, Band 3: Blue, Band 6: SWIR

23. Time Series of land use data

24. Flow Chart of Inundation Map

25. Flood Inundation Map for 2004 & 2007

26. Start, End and Duration of Floods in 2004 & 2007

27. Flood control Works around Dhaka City

28. Performance of Flood control works around Dhaka city during 2007

29. Rampura temporary pump station shows negligible impact on drainage congestion

30. Temporary pumps near Hazaribag discharge untreated waste water which cause serious pollution of Buriganga river

31. Retention ponds of Kallayanpur pump station Encroachments gradually increases and reduces retention pond area. Authority should act immediately

32. Dredging in Turag river filsl wetlands of Dhaka west. Serious thread to retention ponds of Goran chatbari pumping stations.

33. Floating mat of waste on Dholai khal indicates poor solid waste management of the Dhaka city

34. Conclusions The main source of floods in Bangladesh is the rainfall in the upper catchment of the Ganges, the Brahmaputra and, the Meghna river basins. The mean monthly rainfall plot of TRMM satellite data shows that the rainfall is higher for both the Meghna and the Brahmaputra basins, during July 2007 than during the last two years.

35. In terms of magnitude and duration, the flood of 2007 was more severe in the Brahmaputra basin than the flood of 2004. The magnitude of the Meghna in the flood of 2007 was well below the magnitude of the flood of 2004. However, the Meghna was in the flood stage above the danger level for a duration that was similar to the river floods in 2004.