| Influenced by global climate change,precipitation’s spatial and temporal characteristics have changed accordingly.This has led to a change in flood characteristics.This paper takes the typical watershed of the Loess Plateau,the Chabagou watershed,as the research object,analyzes the sub-basin situation and the sub-precipitation characteristics and sub-flood characteristics of the watershed,establishes the HEC-HMS sub-flood model of the Chabagou watershed,and thoroughly studies the influence of the sub-flood volume,rain intensity,and rainfall process line shape on the sub-flood volume,flood peak,and flood process line shape according to the staging of the sub-basin.This is very important for exploring the changes in the Loess Plateau production and confluence mechanism and the work of flash flood disaster forecasting and warning.The main research results are as follows:(1)The analysis of land use,silt dam,and vegetation cover data reveals that the shift in spatial distribution is the main change characteristic of land use;the silt dam reached the design silt siltation volume during the period from 2000 to 2008,which led to the reduction of the specific drop of the river channel;the NDVI value shows a significant increasing trend,and the spatial change trend shows the increase of vegetation cover in the whole watershed.This leads to a prolongation of the confluence process time of floods,which produces a delayed trend of peak present time and may cause a franking of the flood process line shape.(2)The analysis of the rainfall characteristics found that the rainfall amount showed a significant upward trend,the rainfall intensity showed a non-significant downward trend,and the rainfall process line shape coefficient αth From the spatial distribution,the rising trend of rainfall is the greatest in the central part of the basin,and the location of the rainstorm center is gradually gathered in the middle of the basin;according to the trend combined with linear prediction model and exponential smoothing prediction model,the spatial and temporal characteristics of future precipitation and rainfall process are predicted;there is no obvious sudden change point of rainfall amount,and the sudden change year of rain intensity and shape coefficient of rainfall process line is 1990.(3)Analysis of the sub-flood characteristics shows that the peak flow rate shows a nonsignificant decreasing trend,the sub-flood volume shows a non-significant increasing trend,the flood process line shape coefficient shows a significant decreasing trend,and the shape of the flood process line in the basin has changed significantly from the original sharp and thin flood to the short and fat flood gradually;the sudden change of the peak flow rate,sub-flood volume,and flood process line shape coefficient is all in 2005.(4)The HEC-HMS sub-flood model of the Chabagou watershed was established by combining the results of the analysis of the sub-rainfall flood characteristics of the watershed and the subsurface conditions for staging,and the rate determination and applicability analysis of the model parameters were carried out for the base and change periods,and it was found that the model could be applied to the study of sub-rainfall floods in the base and change periods.(5)For the simulation of the sub-flood process with different rain intensity only,when the relative difference rate of rain intensity is 157.22%,the different rates of flood peak,3h flood,5h flood,k1,and k2 of the sub-flood process in the base period are 63.63%,109.32%,155.85%,17.95%,and 21.74%,respectively;the different rates of flood peak,3h flood,5h flood,k1,and k2 in the change period are 52.42%,121.26%,180.23%,7.32%,and 26.47%,respectively.k1,and k2 for the variation periods were 52.42%,121.26%,180.23%,7.32%,and 26.47%,respectively.It shows that the variation in rain intensity has the greatest effect on the flood volume,followed by the flood peak.For the simulation of the sub-flood process with only the different sub-precipitation,when the relative difference rate of sub-precipitation is 98.07%,the different rates of flood peak,3h flood,5h flood,k1,k2 for the sub-flood process in the base period are 39.51%,38.93%,51.93%,9.75%,15.49%,respectively;the different rates of flood peak,3h flood,5h flood,k1,k2 for the change period of the various periods were 35.53%,46.40%,69.03%,2.22%,and 15.27%,respectively.It shows that the variation of rainfall has the greatest influence on the flood volume,followed by the flood peak.For the simulation of the sub-flood process in the case of different shapes of the subprecipitation process line only,when the relative difference rates of the sub-precipitation process line shape parameters are 50.71%and 39.20%,the different rates of the flood peak,3h flood volume,5h flood volume,k1,and k2 of the sub-flood process in the base period are 29.84%,26.67%,47.92%,10.00%,and 16.44%,respectively;the change The variation rates of flood peak,3h flood,5h flood,k1,and k2 in the period were 43.17%,10.19%,29.57%,17.95%,and 18.31%,respectively.It shows that the variation in the shape of the sub-rainfall process line has a relatively large effect on the flood peak.For the simulation of the sub-flood process with different cases of storm center only,when the relative variation rate of storm center is 37.24%,the variation rates of flood peak,3h flood,5h flood,k1,and k2 of the sub-flood process are 19.68%,6.62%,11.85%,11.43%,and 11.76%,respectively.It shows that the variation of rainfall has the greatest influence on the flood peak,followed by the flood volume. |
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