Author(s): P. Vengadesan; S. A. Sannasiraj; S. Murty Bhallamudi

Linked Author(s):

Keywords: Sediment transport; Impacts of dam; Narmada River; Watershed modelling and SWAT modelling

Abstract: Abstract Morphological equilibrium of coastal areas may be adversely affected by the construction of dams across rivers for various purposes like water supply, irrigation, power generation etc. (Panda et al., 2011). Narmada river is the fifth-longest and the largest westward flowing river in India which drains into the Gulf of Khambhat of the Arabian Sea. Construction of dams on this river and its tributaries might have reduced suspended sediment load, which in turn resulted in an increase in coastal erosion and deterioration of coastal marine ecosystems (Gupta and Chakrapani, 2005). The Sardar Sarovar Dam, a major dam located in the lower Narmada River, was inaugurated in 2017. The Google Earth time-series images indicate that the reservoir ponding activity had started in 1994 itself and the Garudeshwar river monitoring station, located on the downstream of the Sardar Sarovar dam experienced a significant reduction in the sediment load from 1995. In this study, an attempt has been made to quantify the reduction in the amount of sediment supply to the coastal areas due to the construction of the Sardar Sarovar dam using a numerical model. A watershed model has been developed using ArcSWAT for the Narmada watershed to represent conditions existing before the year 1995. The model was calibrated and validated using SWAT-CUP for the periods 1987 to 1991 and 1992 to 1995, respectively. The model was then used to simulate average annual sediment load for the period 1995 to 2005 for the Garudeshwar monitoring station. Model results are compared with the field data. These results indicate that there has been a significant reduction in the sediment load from 1992 and the condition deteriorated post-1995. Gupta and Chakrapani (2005) estimated that around 60-80% of sediment was trapped by the Sardar Sarovar Dam from 1996 – 1999. On the other hand, comprehensive numerical model simulations in this study show that the Sardar Sarover dam could be trapping as much as 90% of the incoming sediment. This quantification is essential to assess the impacts of the dams over the sediment movement and conduct the impact assessment for dams over the downstream areas, including morphological changes in coastal areas. References: 1.Gupta, H., & Chakrapani, G. J. (2005). Temporal and spatial variations in water flow and sediment load in Narmada River Basin, India: natural and man-made factors. Environmental Geology, 48(4), 579-589. 2.Panda, D. K., Kumar, A., & Mohanty, S. (2011). Recent trends in sediment load of the tropical (Peninsular) river basins of India. Global and Planetary Change, 75(3–4), 108–118.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022727

Year: 2022