Assessing the applicability of conceptual hydrological models for design flood estimation in small-scale watersheds of northern China

The estimation of design flood is mainly focused on the peak flow and the volume, ignoring the underlying surface factor and flood rising and falling process. Three basic conceptual hydrological models, XAJ, TANK and SCS, are selected and applied for design flood estimation in two small-scale basins of northern China. Model parameter calibration is based on both the optimization algorithm SCE-UA and artificial adjusting, by using a combined objecting function of flood peak, volume and process. Each model singles out a set of optimal parameters as input to simulate the design flood process. The simulation results are compared with original engineering design standards and instantaneous unit hydrograph method. The results show that the XAJ model has the best performance in simulating the 100-year design flood in study basins. The SCS model also gives acceptable results, but the TANK model on the other hand in an underestimated flood peak with a prolonged recession period, which is not likely to be applicable. This study is to test the applicability of the conceptual hydrological models in simulating the design flood process in small-scale watersheds and should be a supplement to the traditional methods and further deliberation to a ungauged basin. Starting from the most basic models with simple structures, it is hoped that the methodology can be transferred to more complicated and physically based models with more realistic description of the rainfall-runoff transformation mechanism and dynamic mechanism for climate change.