Analysis of Basin Scale Processes in Narmada River, India Using Suspended Load Data

The study of suspended load dynamics can give insights into various geomorphic processes in river channels along with events occurring in the respective catchments. This study analyses 28 years of daily suspended load data at eight gauging stations of the Narmada River in peninsular India to understand various geomorphic processes. The Narmada is the largest west flowing river in India and drains 98,796 km2 basin area. The suspended load data is divided into coarse + medium sediments and total suspended sediment (coarse + medium + fine). Rating curves are obtained for all the stations by plotting concurrent suspended sediment concentration versus corresponding water discharge. The slope of rating curves increases downstream from upstream station 1 to station 6, indicating high sediment availability for transportation as we move downstream. The slope for rating curves for total load is found to be consistently high (1.67 to 2.38), which denote higher soil erosion from upstream catchment area and erosion from unstable banks. Rating curves for stations 1 to 6 also exhibits a clock-wise hysteresis behaviour. However, no clear hysteresis pattern is observed in the case of the last two stations, which are each downstream of two major dams, namely Indira Sagar Dam and Sardar Sarovar dam. Further, hysteresis in rating curves disappeared when sediment concentrations are plotted with direct runoff instead of total runoff. Thus the sediment concentration is proportional to direct runoff which in turn is a result of precipitation in the catchment. This indicates that a significant part of the total suspended sediment load is eroded from the catchment.