Hydrologic Characteristics of Floods in Ganges-Brahmaputra- Meghna (GBM) Delta A.K.M. Saiful Islam Sujit Kumar Bala Institute of Water and Flood Management.
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Hydrologic Characteristics of Hydrologic Characteristics of Floods in Ganges-Brahmaputra-Floods in Ganges-Brahmaputra-
Meghna (GBM) DeltaMeghna (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”29th 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
2007 2004 1998 1988
Brahmaputra 0.88 0.68 0.87 1.12
Ganges - - 0.94 0.62
Meghna 0.69 1.53 1.08 1.41
Duration of flood above DL
2007 2004 1998 1988
Brahmaputra 21 15 67 16
Ganges 0 0 26 23
Meghna 37 38 67 75
Floods in Major Rivers1988 1998
2004 2007
Brahmaputra at Bahdurabad
17
18
19
20
21
30-J
un
10-J
ul
20-J
ul
30-J
ul
9-A
ug
19-A
ug
29-A
ug
8-S
ep
18-S
ep
28-S
ep
Wat
er L
evel
(m
,PW
D)
1988
1998
2004
2007
DL
RHWL
RHWL
DL
Ganges at Hardinge Bridge
8
9
10
11
12
13
14
15
16
30-J
un
10-J
ul
20-J
ul
30-J
ul
9-A
ug
19-A
ug
29-A
ug
8-S
ep
18-S
ep
28-S
ep
Wat
er L
evel
(m
,PW
D)
1988
1998
2004
2007
DL
RHWL
RHWL
DL
Meghna at Bhairab Bazar
4
5
6
7
8
30-J
un
10-J
ul
20-J
ul
30-J
ul
9-A
ug
19-A
ug
29-A
ug
8-S
ep
18-S
ep
28-S
ep
Wat
er L
evel
(m
,PW
D) 1988
1998
2004
2007
DL
RHWL
RHWL
DL
Flood Inundation Map based on MODIS Satellite Data
Land Use Classifications
MODIS derived Indices
REDNIR
REDNIRNDVI
15.765.2
BLUEREDNIR
REDNIREVI
SWIRNIR
SWIRNIRLSWI
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
-0.5
0
0.5
1
1.5
2
2.5
3
3.5Ju
l-22
Jul-2
7
Aug
-01
Aug
-06
Aug
-11
Aug
-16
Aug
-21
Wat
er L
evel
diff
eren
ce in
m,P
WD
Goran chatbari
Kallayanpur
Dholai Khal
Segun bagicha
Rampura
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 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.
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