| Based on field investigation and historical data analyzing, the characteristics and causes of flood disasters of Qinba Mountain area were discussed in this paper. Take the harnessed Watershed (Yingwugou Watershed) and unharnessed Watershed (Xigou Watershed) as comparative study objects, through analzing the two typical watershed land using and rainfall-runoff dynamic data, combinating the in-situ soil infiltration field testing, a rainfall-runoff model of small watershed which was appropriate to Qinba Mountain areas was built based on improving the SCS model. And then the influence of soil and water conservation measures on the flood processes was analysed. The main conclusions are as follows:1) Due to large amount of precipitation, frequent rainstorms, mountains development, except for a few basins, flood disasters in Qinba Mountain area were frequent, widely distributed and harmful. Shanxi Province ShangNan County is located in the QinBa Mountain area. Because of specific climatic conditions and geology and physiognomy features, the county suffered montane flood disaters frequently. The flood disaster in this area had the characteristics as unexpected strong, difficulty of prediction and prevention, destructive, in large quantities, uncurbed focus and so on.2) There were two main reasons that leaded to flood disaster in QinBa Mountain area: natural factor and human factor. Natural factor which was the objective condition for the flood disaster taking place included rainfall and topographic and geologic factor; human factor that was people went against the law of nature for social activities reduced the hydrological effectiveness of the watersheds, and was the main reason for the flood disaster.3) Comprehensive management of soil and water conservation improved watershed runoff storage capacity effectively. In the experimental watersheds, flood peak time of treated watershed was delayed by 30 minutes to 60 minutes comparing to the untreated watershed. As to different precipitation, rainfall intensity, this reduction degree of the peak flow was various. Comprehensive management could not only reduce 14%~90% of the peak flow and 25%~71% of the runoff coefficient; but also adjusted the year distribution of rainfall-runoff in small watershed. So the dry season flow increased, and the flood season flow reduced.4) The steady soil infiltration rate was influenced by different land using, and the soil steady infiltration rate of the study watersheds showed the law that woodlandï¹¥turfï¹¥riverside landï¹¥sloping landï¹¥wasteland. It could be seen that the plant measures had a great influence on the steady soil infiltration rate; soil and water conservation measures influenced the flood process primarily by changing the underlying surface conditions.5) The CN value of different land using in average humid circumstances (AMC II of the model) had been brought forward which was suitable for the study watersheds in Qinba Mountain area. The simulation results showed that the simulated and measured runoff process was much closed, and relative error was less than 18% which indicates that the model could be applied to small watersheds in Qinba Mountain area. A scientific method for further study of the comprehensive management configuration patterns and rainfall-runoff forecast in Qinba Mountain area had been offered.6) Contrasting the rainfall-runoff before and after comprehensive management in Yingwugou watershed, we saw that the influence of soil and water conservation measures on the floods was different according to precipitation, time and rainfall intensity. Soil and water conservation measures reduced 23%~85% of the peak flow and made runoff coefficient fallen by 29%~75%.
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