CHAPTER 16
Embankments and Their Ecological Impacts:
A Case Study from the Tropical Low-Lying Coastal
Plains of the Deltaic Sunderbans, India
Asokkumar Bhattacharya
16.1
Introduction
The deltaic Sunderbans occupy 4267 km 2 along the northeast coast of India (21°32 '22°40' N'; 88°05' -89°0' E), and are bounded by the Hooghly river in the west, the Haribhanga river in the east, the Bay of Bengal in the south, and the Dampier-Hodges demarcation line in the north (Fig. 16.1). There are 54 islands of various shapes and sizes
separated by a network of tidal channels, inlets and creeks, some of which act as pathways for both upland freshwater discharge and the to-and-fro movements of flood and
ebb waters (MandaI and Ghosh 1989). In many areas the island margins are protected
by embankments whose combined length amounts to about 3500 km (Sharma 1994).
Some of these large-scale constructions have sluices for the drainage of trapped saltwater.
Embankments act as major elements in the coastal defence of the low-lying coastal
plains and islands. They are constructed near the intertidal borders of rivers, tidal inlets and creeks in order to protect agricultural and inhabitable land from saltwater
inundation. Their combined length of roughly 3500 km is often strongly reduced as a
result of breaching during devastating seasonal floods.
The embankments are maintained by the state government in order to protect the
interests of local inhabitants in the Sunderbans region. In a multi-faceted attempt to
integrate such activities within a broader framework, the present study deals with the
function, design and efficiency of these large-scale constructions as well as the economic consequences of breaching and ecological impacts of embankments in the
Sunderbans coastal plains.
16.2
Physical Setting
The present -day configuration of the low-lying Sunderbans coastal plains of northeast
India is the result of the combined effects of deltaic depositional processes in the Ganges and Brahmaputra rivers, estuarine depositional processes, tidal depositional processes in the Bay of Bengal, tectonic subsidence of the Bengal basin during the Tertiary,
and a general southerly tilting of the basin during recent times (Biswas 1963; Morgan 1965
Sengupta 1972). The region shows a combination ofland and water bodies incorporating 1) tidal creeks and inlets (2350 km2), 2) halophytes and mangroves (1750 km2), and
3) recently raised shoals (217 km 2 ); (Naskar 1996).
The coastal plains slope gently seawards, and lie largely 7-8 m above mean sea level.
The tidal regime is meso-macrotidal and semi-diurnal (Davies 1964; Bhattacharya 1993).
Embankments and Their Ecological Impacts:
A Case Study from the Tropical Low-Lying Coastal
Plains of the Deltaic Sunderbans, India
Asokkumar Bhattacharya
16.1
Introduction
The deltaic Sunderbans occupy 4267 km 2 along the northeast coast of India (21°32 '22°40' N'; 88°05' -89°0' E), and are bounded by the Hooghly river in the west, the Haribhanga river in the east, the Bay of Bengal in the south, and the Dampier-Hodges demarcation line in the north (Fig. 16.1). There are 54 islands of various shapes and sizes
separated by a network of tidal channels, inlets and creeks, some of which act as pathways for both upland freshwater discharge and the to-and-fro movements of flood and
ebb waters (MandaI and Ghosh 1989). In many areas the island margins are protected
by embankments whose combined length amounts to about 3500 km (Sharma 1994).
Some of these large-scale constructions have sluices for the drainage of trapped saltwater.
Embankments act as major elements in the coastal defence of the low-lying coastal
plains and islands. They are constructed near the intertidal borders of rivers, tidal inlets and creeks in order to protect agricultural and inhabitable land from saltwater
inundation. Their combined length of roughly 3500 km is often strongly reduced as a
result of breaching during devastating seasonal floods.
The embankments are maintained by the state government in order to protect the
interests of local inhabitants in the Sunderbans region. In a multi-faceted attempt to
integrate such activities within a broader framework, the present study deals with the
function, design and efficiency of these large-scale constructions as well as the economic consequences of breaching and ecological impacts of embankments in the
Sunderbans coastal plains.
16.2
Physical Setting
The present -day configuration of the low-lying Sunderbans coastal plains of northeast
India is the result of the combined effects of deltaic depositional processes in the Ganges and Brahmaputra rivers, estuarine depositional processes, tidal depositional processes in the Bay of Bengal, tectonic subsidence of the Bengal basin during the Tertiary,
and a general southerly tilting of the basin during recent times (Biswas 1963; Morgan 1965
Sengupta 1972). The region shows a combination ofland and water bodies incorporating 1) tidal creeks and inlets (2350 km2), 2) halophytes and mangroves (1750 km2), and
3) recently raised shoals (217 km 2 ); (Naskar 1996).
The coastal plains slope gently seawards, and lie largely 7-8 m above mean sea level.
The tidal regime is meso-macrotidal and semi-diurnal (Davies 1964; Bhattacharya 1993).