Research On Warning Indicators Of Flash Flood Disaster Based On Critical Rainfall In Southern Shaanxi And Its Application

Flash flood disaster is a natural disaster caused by rainfall,which is mainly affected by rainfall characteristics and underlying surface conditions.Flash flood disaster occurred frequently in Shaanxi Province,which causes significant casualties and property losses every year.The research of flash flood warning and forecasting in small watershed can provide technical basis and solving measures for prevention and treatment of flash flood disaster.This paper analyzes the causes,characteristics and development trend of flash flood disasters in southern Shaanxi and analyzes the benefits of the work of flood prevention and governance.Using the inverse-water level and TOPMODEL basin hydrological model calculates the warning index aimed at the small basins of lack in data.The empirical formula,the inference formula and the instantaneous unit hydrograph method are used to derive the design flood in the Lengshui River basin.The applicability of each method is determined by analyzing and comparing the calculated results.Conclusions are drawn as follows:Flash flood disaster in southern Shaanxi is mainly caused by sudden heavy rainfall.The atmospheric circulation condition and the terrain factor will not change greatly in short term,therefore,the prevention and governance present situation of flash flood disaster in southern Shaanxi will not have big change in a short period of time.By analyzing the casualties and property losses caused by flash floods in recent years,we can see that the disaster losses have been reduced due to the flood prevention and governance project,and the benefits are obvious.Using empirical formula,rational formula and instantaneous unit line to calculate design flood peak discharge,each method is feasible.And the results of the three methods are different.The analysis showed that the experience formula method considering the influential factors too little,so it can only be used as reference results.The calculated peak flow by using instantaneous unit line is larger.It can be applied to areas with large catchment area.The calculation procedure of reasoning formula is simple and the method can reflect the actual situation of river basin.Reasoning formula has better applicability for the small basin without data.Calculating the rainfall warning index of flash flood about small basins by using inversewater level method.Calculate the critical rainfall under different antecedent soil moisture,which is the immediate transfer of rainfall warning value.That can realize the relatively simple dynamic forecast rainfall.When using inverse-water level to calculate the critical rainfall,in the same soil moisture conditions,the critical rainfall value increases with the increase of time,change speed decreases with the time increasing,and the effects of soil moisture decreases with the growth period;under the same period of time,the critical rainfall decreased with increasing soil moisture,and change speed decreases with the increase of soil moisture decreases,the effect of soil moisture decreases with the increase of soil moisture.Using TOPMODEL to calculated rainfall warning index.The basin DEM data were extracted and processed,and the topographic index distribution curve was obtained.The parameters of TOPMODEL were determined by artificial trial and error.The simulation results show that the TOPMODEL can be applied to the moist areas in Southern of Shaanxi and can simulate the runoff process well.The critical rainfall value was calculated by trial calculation under different soil wetting degree.By comparing and analyzing the critical rainfall by inverse-water level and TOPMODEL,we can see that the warning index by the inverse-water level is smaller,and the warning index by the TOPMODEL model method is larger.Compared with the historical flood data,two methods both can be used to calculate the warning index,and can be applied to the early warning and forecasting of flash flood disaster.