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|Title:||RAINFALL - RUNOFF - SEDIMENT TRANSPORT MODELLING|
SEDIMENT TRANSPORT MODELLING
|Abstract:||Sedimentation is an end process of watershed degradation, watershed being the source area, generates the potential sediment, that is eroded material. The, same area also yield water, the chief agent that entrains, transports,, deposits and consolidates the fragmented material. Watershed degradation is the loss of value over time including the productive potential of land and water accompanied by sediments and salts resulting in inferior quality and quantity of water flows. The loss of soil cover reduces the water retention capacity of the land and hence may result increased runoff which may lead to occasional floods. The structures like reservoirs, irrigation canals, harbours and navigation channels, in spite of meticulous design and construction, have resulted in bringing serious problems of silt and salts. Thus, soil erosion and land degradation problems have to be tackled quickly for optimum utilisation of land besides preventing premature siltation of reservoirs. Various attempts have been made to develop a model which can predict sediment production rate with reliability. But due to the complexity of the process it may not be possible to derive a model which is suitable for field applications. In the present study an attempt has been made to develop a fairly reliable model for predicting the sediment flow rates. Transport of sediment is a dependent function of transport of water in a river system. There is a close interaction between rainfall, runoff and sediment. Thus, the relationship between rainfall, runoff and sediment transport has been done in two separate phases, namely, rainfall-runoff phase and sediment transport phase. (xii) For rainfall - runoff phase, a linear, lumped, Nash Model has been used and for sediment transport phase, a sediment graph model based on instantaneous unit sediment graph was developed for predicting the sediment flow rates. Two watersheds namely,• Karso and Kharkhari, located in DVC (Bihar) and Rajasthan respectively have been selected. Five storms of Karso watershed and two storms of Kharkhari watershed have been considered for the present study. In the rainfall-runoff phase, Direct Surface Runoff were computed by convoluting excess rainfall with the computed Unit Hydrograph Ordinates. Average Instantaneous Unit Hydrograph was derived for these watersheds. In the sediment transport phase the Modified Universal Soil Loss Equation (MUSLE), an event based sediment yield model was used to evaluate a storm wise sediment yield. A process based model was developed for predicting the sediment flow rate. Sediment graphs were predicted by convoluting the excess rainfall with an Instantaneous Unit Sediment Graph (IUSG). A sediment routing function, based on travel time and sediment particle size is used to predict the sediment concentration distribution. Results from both the watersheds showed that the model gives fairly reliable results in predicting the sediment yield.|
|Appears in Collections:||MASTERS' DISSERTATIONS (Hydrology)|
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