Impacts of sediment retention by dams on delta shoreline recession: evidences from the Krishna and Godavari deltas, India

Abstract

River deltas are the major repositories of terrestrial sediment fl ux into the world's oceans. Reduction in riverine inputs into the deltas due to upstream damming might lead to a relative dominance of waves, tides and currents that are especially exacerbated by coastal subsidence and sea-level rise ultimately affecting the delta environment. Analysis of multi-date satellite imagery and maps covering the Krishna and Godavari deltas along the east coast of India revealed a net erosion of 76 km 2 area along the entire 336-km-long twin delta coast during the past 43 years 2000-2005. In the case of the Godavari delta, although the water discharge data do not show any major change, there was almost a three-fold reduction in its suspended sediment loads from 150·2 million tons during 1970-1979 to 57·2 million tons by [2000][2001][2002][2003][2004][2005][2006]. A comparison of data on annual sediment loads recorded along the Krishna and Godavari Rivers showed consistently lower sediment quantities at the locations downstream of dams than at their upstream counterparts. Reports based on bathymetric surveys revealed considerable reduction in the storage capacities of reservoirs behind such dams. Apparently sediment retention at the dams is the main reason for the pronounced coastal erosion along the Krishna and Godavari deltas during the past four decades, which is coeval to the hectic dam construction activity in these river basins.

Monitoring of Eco-Restoration of Mangrove Wetlands through Time Series Satellite Images: A Study on Krishna-Godavari Delta Region, East Coast of India

“…Progressive increase in mangrove loss by salt encrustation is perhaps a consequence of manifold decrease in water discharges and sediment loads through the Krishna and Godavari rivers due to impounding of water at the burgeoning dams in the respective drainage basins (Nageswara Rao et al 2010), depriving the estuarine regions of the freshwater inputs and nutrients. …”

River linking in India: Downstream impacts on water discharge and suspended sediment transport to deltas

“…, of which 95% comes during the monsoon season (Rao et al, 2010). The Krishna now runs dry before reaching the delta more than four months of the year.…”

“…The period 2000-2015 was therefore selected to provide the longest possible period over which river discharge remained relatively stable at current conditions. Conversely, the Godavari river has shown no statistically significant change in mean annual water discharge over the last 50 years (Rao et al, 2010). A 30-year record covering the period 1980-2010 is analyzed for the Godavari.…”

An Appraisal of Geomorphic Characteristics and Flood Susceptibility Zone using Remote Sensing and GIS: A Case Study in Bongaon Subdivision, North 24 Parganas (West Bengal), India

“…In Bongaon sub-division, floods are caused by the combination of natural and human factors [4] . However, paleogeographic studies of Ganga delta indicated that the Bhagirathi and Hooghly river has changed their course towards east through space and time with the evolution of the deltas of the peninsular river [5] . The river Ichhamati accumulate discharge from several rivers, e.g., Naobhanga, Jamuna, Padma, Sonai, Ko Hakar, Sonai, Saratkhal and Datvanga and also flood spills from many other channels connecting the adjoining baors and beels.…”