201
140,000 m
3
/s carried by Ganges-Brahmaputra-Meghna (GBM) Rivers (EGIS 2000).
As a whole the Brahmaputra (Jamuna) River carries water flow 60,000–100,000 m
3
/s.
The minimum water flow of the Meghna River is 3750 m
3
/s (Fig. 6.6). The Ganges
River is the major source of silt deposition and delta formation in the Bay of Bengal
(Joseph 2006; Islam and Gnauck 2008). The Brahmaputra carries every year, about
600 million tons of sediments, with alluvial sand constituting large proportion (FAP
24 1996). The sediment is deposited as dunes in the river bed, which is about 350,
in some cases up to 600 m long and they can move very fast as 17 m/s (FAP 24
1996; EGIS 1997).
The Meghna Delta is the main output of the Ganges, the Brahmaputra and the
Meghna to the Bay of Bengal (Chowdhury 1990). The sediment load is extremely
high, with suspended sediment load during flood stage reaching as high as 13 million tons per day (Coleman 1969). The strong south Asian monsoon and high
Himalayan source area supports one of the world’s largest riverine sediment loads
(1.8–2.4 billion tons annually) for the Ganges-Brahmaputra-Meghna dispersal system (Anwar 1988; Umitsu 1993; Goodbred and Nicholls 2004).
The study finding has asserted that India’s diversion of fresh water had resulted
in a loss of biodiversity and rice output of 236,000 metric tons in 1976 just after
construction of Farakka Barrage in India, this loss figure in 2007 became three times
more than the loss of 1976 (Islam and Gnauck 2009a). The previous study result of
CEGIS then EGIS (Environmental Geographical Information System) showed that
the water quality of Sundarbans region has degraded in dry season (February–June),
when 60% water of Sundarbans rivers are poor quality where EC dS/m is 5532 and
40% is good quality and the EC dS/m is 2766 (Islam and Gnauck 2009a). Coastal
water pollution such as oil spills are new threat and could cause immense damage,
especially to aquatic fauna, seabirds, mangrove biodiversity and coastal agricultural
cropping systems. The yearly natural calamities, global warming and its impacts are
new challenge and threats for coastal food security and agro-biodiversity (Islam and
Gnauck 2009b).
As per an earlier soil investigation conducted by SRDI in 1970, the soil salinity
was mainly found in the Ganges tidal floodplain of the coastal region. The Ganges
River floodplain and the peat basins areas were classified as a non-saline. Soil salinity occurred south of Khulna and Bagerhat districts. The surface and subsurface
salinization is very common, with saline water intruding into freshwater aquifers.
Each year, a new area of 146 km
2
is affected by salinity, where a significant reduction in biodiversity is observed (Dutta and Iftekhar 2004). Salinity range was
between 8644 and 17,288 dS/m. A rise of soil and water salinity has been noticed in
1975 when Farakka Barrage constructed on the Ganges River and withdrawal fresh
water from the basin. At present soil salinity level has recognized at south of Khulna
and Bagerhat town ranges between 17,288 and 32,415 dS/m during the dry season
(November–May). Soil and water salinity is rapidly increasing in the coastal region,
currently, river water salinity moves up as far as Kamarkhali River port in Magura
district; (SRDI 1997, 2000; EGIS 2000; Islam and Gnauck 2008). The salinity
trends is higher in the Sathkhira, Khulna, Bagerhat, Borguna, Jhalokhati, Potuakhali,
Bhola and the southern part of Noakhali districts. The trends are higher in the south
6 Degraded Coastal Wetland Ecosystems in the Ganges-Brahmaputra Rivers Delta…
140,000 m
3
/s carried by Ganges-Brahmaputra-Meghna (GBM) Rivers (EGIS 2000).
As a whole the Brahmaputra (Jamuna) River carries water flow 60,000–100,000 m
3
/s.
The minimum water flow of the Meghna River is 3750 m
3
/s (Fig. 6.6). The Ganges
River is the major source of silt deposition and delta formation in the Bay of Bengal
(Joseph 2006; Islam and Gnauck 2008). The Brahmaputra carries every year, about
600 million tons of sediments, with alluvial sand constituting large proportion (FAP
24 1996). The sediment is deposited as dunes in the river bed, which is about 350,
in some cases up to 600 m long and they can move very fast as 17 m/s (FAP 24
1996; EGIS 1997).
The Meghna Delta is the main output of the Ganges, the Brahmaputra and the
Meghna to the Bay of Bengal (Chowdhury 1990). The sediment load is extremely
high, with suspended sediment load during flood stage reaching as high as 13 million tons per day (Coleman 1969). The strong south Asian monsoon and high
Himalayan source area supports one of the world’s largest riverine sediment loads
(1.8–2.4 billion tons annually) for the Ganges-Brahmaputra-Meghna dispersal system (Anwar 1988; Umitsu 1993; Goodbred and Nicholls 2004).
The study finding has asserted that India’s diversion of fresh water had resulted
in a loss of biodiversity and rice output of 236,000 metric tons in 1976 just after
construction of Farakka Barrage in India, this loss figure in 2007 became three times
more than the loss of 1976 (Islam and Gnauck 2009a). The previous study result of
CEGIS then EGIS (Environmental Geographical Information System) showed that
the water quality of Sundarbans region has degraded in dry season (February–June),
when 60% water of Sundarbans rivers are poor quality where EC dS/m is 5532 and
40% is good quality and the EC dS/m is 2766 (Islam and Gnauck 2009a). Coastal
water pollution such as oil spills are new threat and could cause immense damage,
especially to aquatic fauna, seabirds, mangrove biodiversity and coastal agricultural
cropping systems. The yearly natural calamities, global warming and its impacts are
new challenge and threats for coastal food security and agro-biodiversity (Islam and
Gnauck 2009b).
As per an earlier soil investigation conducted by SRDI in 1970, the soil salinity
was mainly found in the Ganges tidal floodplain of the coastal region. The Ganges
River floodplain and the peat basins areas were classified as a non-saline. Soil salinity occurred south of Khulna and Bagerhat districts. The surface and subsurface
salinization is very common, with saline water intruding into freshwater aquifers.
Each year, a new area of 146 km
2
is affected by salinity, where a significant reduction in biodiversity is observed (Dutta and Iftekhar 2004). Salinity range was
between 8644 and 17,288 dS/m. A rise of soil and water salinity has been noticed in
1975 when Farakka Barrage constructed on the Ganges River and withdrawal fresh
water from the basin. At present soil salinity level has recognized at south of Khulna
and Bagerhat town ranges between 17,288 and 32,415 dS/m during the dry season
(November–May). Soil and water salinity is rapidly increasing in the coastal region,
currently, river water salinity moves up as far as Kamarkhali River port in Magura
district; (SRDI 1997, 2000; EGIS 2000; Islam and Gnauck 2008). The salinity
trends is higher in the Sathkhira, Khulna, Bagerhat, Borguna, Jhalokhati, Potuakhali,
Bhola and the southern part of Noakhali districts. The trends are higher in the south
6 Degraded Coastal Wetland Ecosystems in the Ganges-Brahmaputra Rivers Delta…