Role of Climate and Topography on Hydrological Characteristics of the Bharathapuzha Basin in the Tectonically Quiescent Western Ghats, India

Intra-basin variations in sediment supply provide clues for understanding the erosion process and the role of local topographic features and climatic factors. Hence in this study, Bharathapuzha (BP) basin from tectonically quiescent Western Ghats (WG) was selected to examine the role of topography and climate on the sediment erosion process across its sub-basins. Multi-years daily water discharge and sediment load data of five monitoring stations were combined with morphometric parameters to visualize the local variability in sediment erosion rates. The average annual water discharge and sediment load of the BP basin to the Arabian Sea are 4.71 km(3) and 0.37x10(6) tons. Interestingly, Kunthipuzha (KP) sub-basin, despite covering 17% of the total basin area, contributes around 41% and 27% of water discharge and sediment flux, respectively. The sediment yield (erosion rate) from the KP sub-basin is ten times higher than the same sized sub-basin within the BP catchment. For comprehending the role of topography and climate on these local variations, geomorphic indices such as Hypsometric integral (HI) and stream length (SL) index were calculated for the BP basin and sub-basins. Further, multiple regression was used to explore the quantitative relationships among the influencing factors. Results suggest that the rainfall and topography critically influenced basin erosion and explained 93% of the total variance. This study demonstrates the importance of intra-basin scale processes even for small mountainous rivers and signifies the role of local variations in topography and climate in erosion and material transport.