61
The phenomenon of erosion is more serious in coastal areas devoid of vegetations (like mangroves, saltmarsh grass etc.). Many embankments in Indian
Sundarbans face such erosive action where there is no vegetation (Fig. 3.3).
Global warming is accelerating the process of erosion in coastal and estuarine
zones either through increased summer flow from the glaciers or by increased tidal
action (in terms of amplitude) due to sea level rise. It is evident that in Indian
Sundarbans region erosion and accretion almost occur simultaneously. The western Indian Sundarbans exhibits more erosion compared to deposition (Fig. 3.4),
which is reverse in case of central Indian Sundarbans. Erosion is also common in
the southern face of south facing islands of Indian Sundarbans.
The net result, however, is inclined towards erosion as the total area eroded is
almost 283.58 km
2
, whereas the total area of accretion is 83.97 km
2
(Ganguly
et al. 2006).
The phenomena of erosion and accretion are largely regulated by littoral current
pattern and sediment influx from different rivers and adjacent Bay of Bengal.
However, anthropogenic causes like dam construction and water discharge from the
upstream regions are also important factors. There are two major dams on the River
Ganga. One at Haridwar which diverts much of the Himalayan snow melt into the
upper Ganga canal, built by the British in 1854 to irrigate the surrounding land.
This caused severe alteration to the water flow in the Ganga. The other dam is at
Farakka, close to the point where the main flow of the river enters Bangladesh, and
Fig. 3.3 Severe erosion in intertidal mudflat without any mangrove vegetation
3 Mangroves: A Barrier Against Erosion
The phenomenon of erosion is more serious in coastal areas devoid of vegetations (like mangroves, saltmarsh grass etc.). Many embankments in Indian
Sundarbans face such erosive action where there is no vegetation (Fig. 3.3).
Global warming is accelerating the process of erosion in coastal and estuarine
zones either through increased summer flow from the glaciers or by increased tidal
action (in terms of amplitude) due to sea level rise. It is evident that in Indian
Sundarbans region erosion and accretion almost occur simultaneously. The western Indian Sundarbans exhibits more erosion compared to deposition (Fig. 3.4),
which is reverse in case of central Indian Sundarbans. Erosion is also common in
the southern face of south facing islands of Indian Sundarbans.
The net result, however, is inclined towards erosion as the total area eroded is
almost 283.58 km
2
, whereas the total area of accretion is 83.97 km
2
(Ganguly
et al. 2006).
The phenomena of erosion and accretion are largely regulated by littoral current
pattern and sediment influx from different rivers and adjacent Bay of Bengal.
However, anthropogenic causes like dam construction and water discharge from the
upstream regions are also important factors. There are two major dams on the River
Ganga. One at Haridwar which diverts much of the Himalayan snow melt into the
upper Ganga canal, built by the British in 1854 to irrigate the surrounding land.
This caused severe alteration to the water flow in the Ganga. The other dam is at
Farakka, close to the point where the main flow of the river enters Bangladesh, and
Fig. 3.3 Severe erosion in intertidal mudflat without any mangrove vegetation
3 Mangroves: A Barrier Against Erosion