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.