MODELLING SEDIMENT YIELD FROM NATURAL WATERSHEDS

Abstract

The rainfall-runoff-soil erosion process in a watershed is a very complicated phenomenon that is controlled by a large number of known and unknown climatic, geologic and physiographic factors that vary both in time and space. Several models, varying in complexity from lumped empirical to physically based, time and space distributed, are available in literature to model soil erosion and consequent sediment yield. The physically based models have proved very useful as a research tool but are of limited use in field, especially in developing countries like India, because they require large amount of data. Nevertheless, search is still continuing for developing new and simple models. In the present research work, an attempt has therefore been made to develop event-based, lumped and time-distributed simple sediment yield models using the well-accepted hydrologic concept of proportional equality of the Soil Conservation Service Curve Number (SCN-CN) method and the upland potential erosion, normally estimated by erosion equations such as the Universal Soil Loss Equation (USLE). To start with, a detailed survey of the published works relating to rainfall-runoff-erosion modelling was carried out. Because of the close dependence of sediment yield process on surface runoff, a sediment yield model utilizes either a lumped estimate of surface runoff for computing total sediment yield from a storm event or a suitable infiltration model is employed to generate temporally varying rainfall-excess (or runoff rate) that is primarily responsible for delivering the sediment at the watershed outlet.