Subsidence of the Ganges—Brahmaputra Delta of Bangladesh and Associated Drainage, Sedimentation and Salinity Problems

The Ganges—Brahmaputra Delta is one of the most densely populated areas of the world. The delta occupies most of the Bengal Basin and is slowly subsiding as a result of isostatic adjustment of the crust due to rise of the Himalayas and dewatering of the Proto-Bengal Fan sediments which is now buried under thick Mio-Pliocene-Pleistocene deltaic sediments. Well-log data from northwest of Dhaka indicates that at least a part of the basin is subsiding at a rate of 2.2 cm/year. Three areas of the basin — the Hatiya Trough, Faridpur Trough and Sylhet Trough — may be subsiding at similar or higher rates. Engineering projects that do not consider the subsidence component in planning and designing may produce results detrimental to the environment.The subsidence and the relative sea-level rise could cause serious drainage and sedimentation problems in the Ganges-Brahmaputra Delta. With higher sea level, more areas will be affected by cyclonic surge; inland fresh water lakes, ponds and aquifers are likely to be affected by saline and brackish water intrusion. The present limit of tidal influence is expected to extend further north. Expected sea-level rise will cause soil salinity, as well as surface water and ground water salinity for a large part of the coastal area. The above conditions, together with lack of dry-season stream flow, may cause serious ecological and economic problems for the country.