Understanding runoff processes using a watershed model—a case study in the Western Ghats in South India

The wet tropical Western Ghat Mountain ranges in South India present an interesting combination of meteorological and physical characteristics. The results of a watershed model analysis carried out to understand the catchment response and the relative importance of different runoff processes in the region are reported in this paper. A lumped parameter model simulating saturated source area runoff, lateral flow through pipes and the saturated zone groundwater flow, has been developed assuming that source area runoff is the only quickflow component. The model has been calibrated on seven catchments using sufficiently long records of daily data. A wide range of tests has been used to show that the model performs reliably. The influence of catchment characteristics on the relative importance of the flow components and the catchment response has been studied. The model simulations have been interpreted to infer that the pipeflow contributions augment the contributions of source area runoff to stream quickflow. Suggestions for further research in the area are given, based on the inferences drawn

Runoff processes in headwater catchments—an experimental study in Western Ghats, South India

Field observations and experiments were conducted to study runoff in a headwater region in the mountains near the west coast of Karnataka, a south Indian state. Three catchments were studied. Pipeflow was observed in all three cases, and there was no subsurface lateral flow through the soil matrix. Pipeflow was a significant contributor to quickflow in two catchments. In the third, grassed catchment, a new mechanism of runoff, called pipe overland flow in this paper, was discovered, which contributed to quickflow. The contributing area for pipeflow increases with the magnitude as well as duration of rainfall, but a dual behaviour with respect to average rainfall intensity shows up in one of the catchments