Study On The Method Of Designed Flood Peak Flow Calculation In Ungaged Basin

Due to the influence of extreme rainstorm weather,mountain area flood poses great damage and threat to people’s property security and infrastructures of mountain area.As one of the earliest methods of calculating flood from rainstorm,the rational formula method is more suitable for calculating rainstorm flood in small watershed.This study aims at the existing problems of the rational formula method,putting forward the improvement method,and the improved method is applied to the study basin,and the design flood peak value is compared and analyzed.The main research contents and achievements are as follows:(1)Under a certain flow generation duration tc,the flow velocity v is assumed to be the determined value.The confluence path length Ltc can be used to calculate the corresponding maximum runoff area Ftc,and obtain the Ftc and Ltc relationship.Based on DEM data and ArcGIS software,the relationship between Ltc and Ftc is obtained through programming.(2)The experience formula can be used to calculate the flow velocity v and the flow generation duration tc under the design flow.By multiplying the two,the confluence path length Ltc can be obtained.By using the function relation between Ftc and Ltc,the quantitative calculation method of maximum runoff area Ftc is obtained.The improved reasoning formula is obtained by using the basic form of rational formula and quantitative method for Ftc.(3)The rational formula before and after the improvement is applied to the design flood peak flow calculation in 11 basins,and the results showed that the value of flood peak flow calculated by the improved rational formula method is larger than that before and relatively safe.(4)Analyze the influence of basin area,difference between catchment confluence time and runoff duration,and basin shape coefficient on the error of calculation results.The results show that in the case of partial confluence,basin area and the difference impact strong positive correlation between the error before and after improvement,and there is also a strong positive correlation between basin shape coefficient and the error.