Study of creek systems of the western Sunderbans with special reference to appraisal of the georesources of the tidal domain

摘要

An understanding of the evolution in georesources within the tidal domain could be made through closer appreciation of tidal landforms relating to creek systems. Historically and traditionally, landform units of tidal regime of the Sunderbans have collectively been looked upon as resources for both survival and livelihood. A change in hydraulic regime of the tidal system over last several centuries is manifested in creek systems and hence the quality of the micro-landform units and pattern of their utilisation has witnessed major transformation. With deterioration of discharge along trunk channel of Ganga River, the downstream drainage network and tidal creeks were flushed only with tidal flows. Thus the creek systems, many of which were earlier having sufficient draught for large vessels to ply, had been abandoned and a similar fate followed for some of the ancient habitations. Major changes in land use practices in Sunderbans during British period brought new settlements and the process of building up of land in the intertidal marshes by tide-borne silts carried by creeks was arrested. The creeks further witnessed shallowing of channel beds, changes in configuration of channel bars and tidal flats. The georesources of creeks and associated landforms went through modifications partly due to anthropogenic interference and because of natural instability of the tracts. The study by Geological Survey of India in recent years (2005-2009) indicates that many of the creeks and minor cross channels show rapid deterioration in the north, while outfall points of major creeks show extensive modifications in channel morphology. Various in-channel landforms including channel bed geometry, tidal flats, mid-channel shoals and bars and creek margins have been studied extensively during the survey and their resource potential assessed. As the trend of changes in tidal domain is complex in nature, flexibility in landform- resource utilisation and principle of sequential land use practice should be incorporated in perspective planning of landform-georesources of this fragile domain at land-sea interface. The present study aims at bringing together geological history of the trunk river (Bhagirathi) and the evolution of creek systems of Sunderbans into a broad framework of tidal georesource potential—a step towards this objective.