DEM-Based Hydrological Model And Nonlinear Confluence Problems

Distributed Hydrological Models have become the trend for hydrological modelling due to their abilities to provide powerful tools that are scientifically realistic in the description of runoff formation mechanics in the real world; extensive researches on the application of same have proven its great theoretical value and practical meaning. Based on the Digital Elevation Model, a grid-based distributed Xinanjiang Model is developed with extension of discussions on the nonlinear confluence problems.The approach adopted in this study involves a comprehensive review of methods concerned with extraction of basin characteristics; this includes stream classification according to Strahler, slope derivation, calculation of gull density. Based on Digital Elevation Model, Xinanjiang Model is used on one grid to calculate evaporation, runoff, water resources separation and confluence by considering one grid as one calculated basin. The Alg-Route Method was employed for basin confluence and the Grid-Based Muskingum Flow Routing Method for river system. The grid-based Xinanjing model was applied for flood simulation to the Upper Lushi basin in Luo River and Upper Misai basin in Qujiang River based on the preceding pre-processing. The results show that the model can perform well not only in humid areas but also in semi-humid areas.Nonlinearity in basin concentration has become a great problem in hydrologic modeling. In the Xin'anjiang model the surface runoff concentration is usually neglected; the Alg-Route Method is traditionally employed for the river confluence in sub-basins but this approach lacks specific hydraulics basis. To this end, two nonlinear reservoir equations are developed to describe surface runoff and river confluences respectively. The variable order Runge-Kutta method developed by Cash and Karp was employed to solve the two nonlinear equations while the parameters for the confluence were determined according to the basin information extracted from DEM. The model was applied for flood simulation to the Upper Misai basin. Results obtained show fast declining flood which might be due to kinematic wave (hypothesis).