Hazards from Man’s activities
Stress on marine life and resources
Undersize fishing, fishing in breeding season, use of detrimental fishing gear, and building of dams and embankments are posing major threats to the fish resources of West Bengal coast inclusive of the Sundarban areas. Added to this, pollution of estuarine and coastal water has led to survival of only pollution resistant aquatic species and depletion of bio-diversity in certain parts of the coastal water bodies. West Bengal government is trying its best to stop the bad practices. Due to shrinking fish population many fishermen in these areas are compelled to leave their profession. Fishing on permit basis is now limited to the buffer area of Sundarban. But large scale catching of tiger prawn seeds in Sundarban is causing reduction in mullet population of other fishes.
Dredging in and around Haldia port
Haldia being an estuarine port on a major river, the channels leading to the port requires regular maintenance dredging for keeping a minimum draft to allow large ships to anchor in the port. The dredged materials are often disposed in the channel itself away from the ship channels. The channels over years show migration from one path to another within the wide funnel shaped estuary some times making capital dredging essential to open up a channel with adequate draft. River training works to maintain the dredged channel is also part of the maintenance work. Although dredging is unavoidable in and around the Haldia port, nevertheless it disturbs the bottom dwelling organisms and their habitat.
Oil and hazardous waste spilling
The major incidents that lead to oil spills are the collision, grounding and other accidents by ships and especially tankers that carry petroleum products to the Haldia and Kolkata ports and such vessels cruising off from Paradeep port. The coastal pipelines carrying petroleum crude from Paradeep to Haldia and Haldia to Barauni are also susceptible to accidental leakage in coastal area through which they pass. Minor oil spills may occur in coastal areas of Sundarban and off-shore areas of West Bengal coast (having fishing and other activities involving mechanized boats) from accidents involving fishing trawlers, ferry launches carrying passengers and ships/barges carrying various cargos including those carrying fly ash to Bangladesh. The port facilities at Haldia and Kolkata and Indian Oil Corporation installations are having arrangements and protocols in place that prevent collision and/or grounding of ships/tankers/barges. Even then absence of more advanced navigational instruments and human error may lead to oil spills endangering marine life. Appropriate contingency plans that are in place require constant review and upgradation so as to tackle oil spills of at least 100 tonnes. In the inhabited areas of Sundarban, there are considerable riverine traffic for various communication and economic activities. The authorities need to develop contingency plan in case of accidental oil seepage and hazardous waste like fly ash spilling from accidents and/or malfunctioning of the plying vessels.
Seawater intrusion in paddy fields due to failure of embankments
Agriculture is extensively practiced in coastal areas of West Bengal. In the near absence of any surface water irrigation scheme and as ground water occurs at considerable depth, the agriculture is dependent on monsoon rainfall. However, the meso and macro tides along the West Bengal coast coupled with storm surges during the cyclone months tend to flood the agricultural fields with brackish to salt water. To prevent the agricultural fields from salt water intrusion in the Sundarban areas, extensive embankments have been constructed long time back along the creeks of this estuarine track. This embankment system is in various stages of disrepair and often the vulnerable sections are breached leading to flooding of the paddy fields with saline/brackish water. Once a field is polluted with brackish water it takes several monsoon seasons to wash out the salt from the soil back into the creeks so as to make the area suitable for agriculture.
Fresh water depletion and salinity ingress in coastal aquifers
The geohydrological set up of coastal zones of West Bengal is known to a reasonable of detail. A fresh water aquifer sandwitched between two saline/brackish water bearing zones is present along the coast. In areas marked by sandy dune systems along the coast, a shallow fresh water zone is present from surface to a few metres depth. Two areas of concern are Haldia and Digha-Sankarpur. Organised withdrawal of ground water has been in place in Haldia to supplement the fresh water supply from surface sources. To protect the ground water from overdrawal, appropriate statutory notification has been promulgated by Central Ground Water Authority. In Digha-Sankarpur area unregulated shallow to deep tube wells are being sunk for drawal of fresh water. In both places no systematic study has been made to assess whether there is any depletion of fresh water in the region. Further it has also not been investigated whether due to drawal of fresh water whether the wedge of salt water-fresh water interface is moving land wards.