Study On Flood Runoff Variation Characteristics In Dali River Basin

Change of underlying surface condition caused by human activities, changes characteristics of flood runoff in river basin. In recent years, in Dali River basin, annual maximum peak has a significantly decreasing trend; the number and magnitude of floods are reduced; the runoff at the same rainfall level is decreased. There are indications that, due to the impact of human activities,regulation of runoff yield and concentration has changed greatly. This change threatens regional water security. This paper taking Dali River basin as the study area, and choses Qingyangcha basin,Chabagou basin and Xiaoli River basin as research objects. In this paper, we analyzed the trends of rainstorm flood features in each research basin. Conducting flood simulation and analyzing the applicability of the model in Dali River basin based on multi-source Time Variant Gain Model(MTVGM). By the different parameters of runoff yield and flow concentration before and after the change of underlying surface condition, we conduct each magnitude of flood simulation, and estimate the influence degree of the change of underlying surface condition on the regulation of runoff yield and concentration. The main research contents are as follows:(1) According to the remote sensing data of Landsat MSS / TM in Dali River Basin, the vegetation cover changes in the 1970s and 1980s were analyzed. The result shows that the vegetation coverage of each basin increased from 1970s to 1980s. It has an overall trend from low coverage and moderate coverage to high coverage. At the same time, we collect the soil and water conservation measures and size in Dali River basin.(2) Using linear trend regression and Mann-Kendall trend test analyze the trend of the time series of annual maximum peak, flood volume, storm volume and flood peak delay time hydrologic parameters. Use double mass curve method, sequence cluster analysis, smoothing F test and smoothing T test analyze the variation of hydrologic parameters, and determine the aberrance point of parameters.(3) Selecting floods under similar rainfall before and after the variation of rainstorm flood features in each research basin, and comparing the characteristic changes of each flood. The preliminary results show that, the change of underlying surface condition leads to the decrease of flood peak and flood volume.(4) Using MTVGM model to simulate flood, calibrating and verifying the model parameters,the results show that the shapes of simulated flood hydrograph and measured flood hydrograph were fitting good. The error of most flood peak and flood volume is less than 20%, and the value of Nash-Sutcliffe efficiency coefficient is more than 0.7. Therefore, we consider that the model is well suited for the Dali River basin, and the model can be used to analyze underlying surface impact degree on the regulation of runoff yield and concentration. Selecting inundation, medium flood, miniature flood in each research basin to be simulated by different model parameters before and after the change of underlying surface condition. The results show that the change of underlying surface condition leads to the decrease of flood peak and flood volume, and the decay rate increases with the decrease of the flood magnitude, and the decay rate of flood peak rather than the decay rate of flood volume. At the same time, it also leads to flood peak clipping and attenuation actions. Among them, for inundation and medium flood the main role is peak clipping;for miniature flood the main role is attenuation actions.