Study On Distributed Runoff-Sediment Coupled Model In The Middle Reaches Of The Yellow River

Simulation of soil erosion are developing from empirical models and lumped physically-based conceptual models to distributed models along with more findings of human being about soil erosion and the development of computer, GIS and RS.The process of soil erosion is divided into four sub-processes here based on anterior studies. They are slope splash erosion, slope runoff erosion, ditch runoff erosion and gully gravity erosion. Firstly, a distributed runoff model is established based on Hordon infiltration curve and Saint Venant equations, in which, generation and concentration of runoff is calculated by grid to grid. DEM with resolution of 3 " is used to extract catchment properties for flow and sediment transport calculation. Secondly, a distributed sediment yield and transport model is developed based on the relation of speed of soil erosion, corrosive power of runoff, sediment carrying capacity and actual sediment flux. In this model, calculation of sediment transport is in grid to grid and effect of gravity erosion is taken into account.Then the two models are coupled, in which, slope grid is parted into rill and interrill, channel grid is parted into channel and slope based on calculation width of runoff-concentration. Splash erosion calculation is done directly on slope-interrills and slopes of channel grids. Both runoff erosion and splash erosion in rills is calculated at the same time when its runoff is less then 6 mm. And effect of gravity erosion is emphasized on sediment transport for it is difficult to estimate the quantity of sediment yield. Grids with gravity erosion are determined by judging those factors affecting its happening. And assume that sediment production is more than maximum potential carrying capacity of channel runoff after gravity erosion occurred, so actual sediment load of this grid equals to its maximum carrying capacity.Finally, this coupled model is calibrated and validated with observation data of Xiaoli River. Results showed that the coupled model could be used to simulate runoff, sediment yield and transport. It is a try on distributed simulation of water and sediment. The model can give distributed outputs based on calculation of runoff concentration and sediment transport in grid-to-grid, which embodied the potential of distributed water and sediment coupled models.