This study was aimed at analyzing the sediment yield characteristics and its spatial and temporal variation in the tropical river basin of Pamba river, which is one of the major rivers of the State of Kerala. The daily discharge-sediment data pertaining to the Central Water Commission (CWC) gauging site for the period 1986-2006 was used for the analyses. Annual, seasonal and monthly variations in discharge and sediment load were analyzed using this data. In order to study the spatial variation in the sediment yield, three more stations were identified within the river system on major tributaries for sediment monitoring. The sediment contribution from each of these tributaries was also calculated. It was found that the water and sediment transported by the river show a decreasing trend in recent years. The average annual discharge and sediment load of the river are 3,838.6 MCM and 135,427 tons, respectively. The average sediment yield for the river basin is estimated to be 79 tons/km², which is very low compared to that of other major rivers of India. The two monsoons, South-West (SW) and North-East (NE), contribute about 92% of the discharge and 96% of the sediment load. The influence of NE monsoon on sediment production and delivery was also noticed. Hysteresis effect of discharge-sediment concentration relationship was studied, and it was found that the majority of rainfall events produced a clockwise loop.

The study of soil erosion in the upstream river basins, sediment transport and deposition plays a major role in understanding many activities of global significance. Due to various developmental activities within the river basins, the rate of soil erosion, its transport, and deposition downstream have considerably altered. Such changes will have an impact on the river system, reservoirs, estuaries and coastal regions (Chakrapani, 2005). Therefore, comprehensive studies are required to analyze the spatial and temporal variations of sediments transported by the rivers.

Analysis of data indicated that the distribution of rainfall and the topographical characteristics are the major factors influencing the variation of sediment flux in the rivers of Kerala (Chandramohan and Balchand, 2007). Sediment transport from northern rivers is highly influenced by the South-West (SW) monsoon, whereas both the SW and North-East (NE) monsoons control the sediment yield of southern rivers. About 94-98% of the sediment load is carried by the monsoon river flows.

The present study was conducted to investigate the spatial and temporal variations in the sediment transport characteristics of Pamba river basin, which is one of the major river systems of Kerala.

Soil And Water Sciences Journal, Erosion, Sediment Yield, Pamba River Basin, Monsoon, Hysteresis, Soil Erosion, Topographical characteristics, Central Water Commission, CWC, Cochin University of Science and Technolog, CUSAT, Sediment Flux, Sediment Monitorin.