Watershed Flow Routing Researches Based On Digital Terrain Analyses Techniques

Because of traditional methods'limitation, it is difficult to take the spatial variability of hydrological factors into consideration for watershed simulation. The developments of GIS techniques have offered effective tools to obtain, manage, and represent spatial information. By digital terrain analyses (DTA) based on DEM, stream networks and many other spatial characteristics of topography can be extracted. On the basis of watershed stream networks and its spatial characteristics of topography, GIS and watershed models can be integrated effectively. So, spatial variability of hydrology factors can be presented in watershed simulation. In the thesis, the DTA based on DEM is reviewed, and its algorithms for stream networks extraction have been talked about in detail. In the research of flow routing, firstly, watershed stream networks and its spatial characteristics of topography have been extracted by Digital Terrain Analysis, and the rainfall has been interpolated based on the digital river. Secondly, with reference to the traditional flow routing method—isochrones, spatial variability of rainfall and watershed topography are both considered to derive the variable isochrones. Lastly, a digital flow routing model has been established based on variable isochrones and the proposed variable isochrones method has applied for a small watershed. The application shows that, topography is the main factor which influences watershed flow routing, but the rainfall distribution has evidently changed the relationship between time and area. The variable isochrones based on digital stream networks, can overcome the defect in traditional isochrones method, which assumes that flow velocity is even on the whole watershed. The influence of rainfall and watershed topography on flow routing can be both considered in the variable isochrones. By using variable isochrones to compute the discharge hydrograph, the influence of watershed topography can be presented, and the influence of rainfall can also be better reflected.