Geo-historical Appraisal of Embankment Breaching and Its Management on Active Tidal Land of Sundarban: A Case Study in Gosaba Island, South 24 Parganas, West Bengal

Abstract

The embankments act as a life line for deltaic people of the Sundarbans. The reclamation of immature land through the construction of embankment without proper planning has been increasing the vulnerability of embankment breaching due to various natural and anthropogenic causes. The construction and maintenance of embankments are difficult tasks without prior knowledge about the mode of vulnerability and ground situations of the sites. To understand the scenario of embankment breaching and its recent management strategy, an intensive field survey was conducted to comprehend the underlying reasons for embankment breaching and its management techniques at the ground level. The modern techniques were also incorporated to identify the vulnerable sites of river bank erosion. The study reveals that the southern part of the delta is more vulnerable due to intensive river bank erosion. To understand potential capabilities of these embankments to combat against fluvio-hydrological challenges, a sequential change of embankment construction from historical past to present and recent scientific engineering model of Aila Dam has been chalked out in this study. The present study is an attempt to understand the geo-historical perspectives of embankment construction and to identify the vulnerable coastal zone of Gosaba Island of Sundarban. The study also aims to illustrate the modern techniques of embankment management for its longevity in such a dynamic land.

Impact of climate change and management strategies on water and salt balance of the polders and islands in the Ganges delta

“…The area of Gosaba Island in West Bengal is 36 km 2 . The population density in these 3 polders/Islands are 548 person/km 2 , 1024 person/km 2 , and 831 person/km 2 , respectively for Amtali, Dacope and Gosaba 7 , 51 , 52 . The people depend mainly on agriculture for their livelihood 4 , 23 .…”

“…The coastal zone of the Ganges delta in Bangladesh includes 139 polders which are low-lying tracts of land surrounded by dikes constructed in the 1960s and 1970s to protect farming lands from saline water intrusion and tidal floods 6 . A less-well-developed polder system exists in the Sundarbans region of the West Bengal in India 7 . The ground level within polders is mostly within 0 to 3 m above mean sea level 8 .…”

“…This results in fluctuations in river water level of up to 4.0 m. The dense networks of canals (former river distributaries) within the polders are connected to the surrounding rivers by a series of sluice gates under the embankments providing the opportunity to bring water in during high tides, or to drain water from the polders during low tides, as needed. However, water management in the polders is poor, and infrastructures are inadequate, which makes the drainage of rain water accumulated within the polders difficult 4 , 7 , 9 – 11 . Due to insufficient drainage arrangement and high rainfall (~ 2000 mm, mostly concentrated during the monsoon season), polders are prone to flooding during the wet season.…”

“…About 65 percent of the lands of the coastal zones of Bangladesh and West Bengal are affected at various levels (low to high) due to salinity during the dry season 4 , 12 , 13 . Soil salinity is a major, and the most persistent, threat in the coastal zone of Bangladesh 14 and Sundarbans region of West Bengal 7 .…”

“…These areas are disadvantaged by poverty, food insecurity, environmental vulnerability, and limited livelihood opportunities 5 , 16 , 17 . In West Bengal, 44 percent of the population is living below the poverty level and 87 percent people suffer from food shortages 7 . Similarly, in Bangladesh, 30.8 and 37.2 percent of the population of Khulna and Patuakhali districts, respectively, live below the poverty line compared with 24.3 percent for the whole country 15 .…”