Damming effects on the degree of hydrological alteration and stability of wetland in lower Atreyee River basin

Numerous studies have discovered damming effect on downstream river eco-hydrological state but little is thought about its consequences on eco-hydrology of riparian wetlands. Hydrological data scarcity at a spatial scale is one of the major constraints. The present study intends to explore the damming effect on eco-hydrological components like wetland depth, consistency in water appearance, hydrological stability, eco-hydrological failure and eco-deficit using spectral indices from remote sensing data taking Atreyee river basin as a case. Time series Normalized differences water index and Modified normalized differences water index are taken as the database. Range of variability approach and flow duration curve methods are adopted for the computing failure rate of ecological water appearance and eco-deficit in the wetland. The result shows a statistically acceptable positive relation (0.76 to 0.89) between normalized differences water index and modified normalized differences water index value and depth of water in wetland inferring the substitutability of spectral values to depth data. In the post-dam phase (2012 onward) about 82% and 96% wetland area in pre-monsoon and post-monsoon season has turned into a hydrologically unstable state leading to a growing failure rate for attaining ecologically essential water volume and eco-hydro deficit state of wetland. Damming has converted only 100% wetland area into the eco-deficit zone which is ecologically not viable. Based on the findings study recommends that for the survival of the river and wetland ecological flow is required to release from the dam.