| Digital elevation model(DEM) has become widely used in distributed hydrological models. It is found that the automatic detection of drainage networks from digital elevation models is affected by flat areas and closed depressions .A variety of methods have been proposed to treat these two features , but it can be seen that the flat areas and closed depressions are processed only after they have been created ,so that many spurious and parallel drainage courses are generated . It is known that flat areas and closed depressions often arise because of low quality input data, interpolation errors during DEM generation et al., therefore, they can be removed by adding elevation information to input topographic data. The proposed approach can lead to better match between observed and modeled flow structure and produce more realistic results in application.The algorithm for delineation of a drainage network proposed by O'callaghan and Mark is very widely used. A drainage area threshold is used to produce a continuous network, so that different network is obtained for varying drainage area threshold. A method is proposed, in which the relation between source density (or drainage density) and the threshold is used to produce an ideal drainage network ,the area threshold when source density (or drainage density) show stability is reasonable. The method is used in Yanduhe watershed and a good result is obtained.The geomorphological instantaneous unit hydrograph(GIUH) is viewed as the frequency distribution of the times of arrival of individual water deoplets at the catchment outlet.The travel path ,for a typical hillslope cell .consists of a hillslope fraction,corresponding to overland flow and a stream fraction,corresponding to concentrated channeled flow.To obtain the time of travel,velocities must be defined.Hillslope and stream velocities vary with location and must be strongly correlated with slope,and therefore a spatial distribution of velocities and hence of travel times could be obtained.The present methods of GIUH neglect any time delays associated with overland flow pathways.A new method is presented.The travel time,including the time delays associated with overland folw pathways, is obtained.It is expected that the hillslope velocity and the stream velocity are different,and different equation is used.In the method ,the fact that velocity increases going downstream in river systems is taken into account.Afterthe travel time of each cell being calculated,the frequency distribution of the times of arrival of individual water droplets at the catchment outlet -GIUH,is obtained.The topographic index ln(α/tan #) is an important parameter of many physically based hydrological models. TOPMODEL is based on the calculation of ln(α/tan #) index and its distribution .In terms of a DEM, a is the cumulative upslope area draining through per contour length to a pixel, which reflects the tendency of water to accumulate at any point in the catchment, tan # is the local slope angle of the cell, which reflects the tendency for gravitational forces to move that water downslide. The calculation method of ln(α/tan #) index widely used is the multiple flow direction algorithm developed by Quinn et al.It can been seen that, in the algorithm, the contour length normal to the direction of flow flowing out the current cell is used to determine both a and tan # , and that the calculated total cumulative contributing area of downslide grid cell does not include the area of the current cell. These are unreasonable. It is found that the contour length used to determine a should be that normal to the direction of flow entering into the current cell, rather than that flow out the current cell. The algorithm improved to calculate the ln(α/tan #) index is presented, in which the area of the current cell is included in the calculated total cumulative contributing area of downslide grid cell. The different between the results of the two algorithms is described.A simple algorithm for the calculation of topographic index ln(...
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