Monitoring estuarine morphodynamics through quantitative techniques and GIS: A Case study in Sagar Island, India

摘要

Mapping of coastal areas, shorelines, estuarine islands are very important in order to determine the hydro dynamic and hydro meteorological behavior of coastal zone and estuarine deltaic tracts. This paper presents the spatio-temporal changes of morphological configuration of shorelines, river banks of deltaic Sagar Island situated in the mouth reaches of Hugli estuary in India. Passing through the western margin of Ganga delta the Hugli river is flowing to the Bay of Bengal in north south direction and it is dominated by strong tidal current. Being the largest island in Hugli estuary Sagar Island represent variety of inter tidal sub tidal sub-environment formed by estuarine erosional and depositional processes. The study aims to monitor and measure the quantitative changes of shorelines, island area, spatio-temporal variations of erosional and depositional processes and resultant landform assemblages by using shoreline change envelop (SCE), net shoreline movement (NSM) and end point rate (EPR). With the help of multi-temporal maps and image (District map, Police station map of 1912-29, SoI Topographical sheets 1967-69 and IRS P6 LISS IV satellite image of 2014), GIS techniques, mathematical modeling of hydro morphological parameters the present study has given a fruitful result. Measurement of shoreline dynamics clearly shows that coastal shoreline and estuarine bank line erosional processes are very active along south eastern coastal tract, south western part of Sagar Island and exposed concave river banks along the north eastern part of Sagar respectively. Finally is has found that intensity of erosion in Sagar Island is strongly controlled by estuarine exposure, sediment composition, channel flow direction, near bank channel depth, orientation of thalweg line, wave form velocity, long shore velocity, direction of longshore current, episodic cyclonic events with mean high tidal ranges and disturbance in estuarine equilibrium condition.