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

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.

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

River System and GBM Grid

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

Rainfall (May-Sep, 1998)

Rainfall (May-Sep, 2004)

Rainfall (May-Sep, 2007)

Normalized Monthly Rainfall

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

Chronology of the entrance of 2007 Flood

Water Level Stations in Major Rivers

Height of Peak above DL Brahmaputra Ganges Meghna

Duration of flood above DL Brahmaputra Ganges Meghna

Floods in Major Rivers

Brahmaputra at Bahdurabad

Ganges at Hardinge Bridge

Meghna at Bhairab Bazar

Flood Inundation Map based on MODIS Satellite Data

Land Use Classifications

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

Time Series of land use data

Flow Chart of Inundation Map

Flood Inundation Map for 2004 & 2007

Start, End and Duration of Floods in 2004 & 2007

Flood control Works around Dhaka City

Performance of Flood control works around Dhaka city during 2007

Rampura temporary pump station shows negligible impact on drainage congestion

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

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

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

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

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.

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