Research On Deriving Zhouzhi County Rainstorm Intensity Formula

Urban waterlogging problems occur frequently in recent years,which seriously affect the function of the city and the environment,even threatened the city people’s life and property safety,so set up the perfect city drains system is imminent.However,the rainstorm intensity formula is the important basis of city drains system design,so it is particularly important to prepare the scientific and reasonable rainstorm intensity formula.Zhouzhi as a county town of xi ’an,hasn’t yet set up their own rainstorm intensity formula.Therefore,it’s urgent to establish a rain storm intensity formula which obeys the law of zhouzhi to guide the design of the city’s drains system.The author on the basis of minute rainfall data of 20 year in 1996~2015 provided by the Zhouzhi weather bureau.Through the analysis of sampling methods,finally using the annual maximum value method for sampling.In the frequency adjustment,we using Pearson Ⅲ type distribution,Gumbel distribution curve and index distribution curve,and line method and least square method is adopted to solve the theoretical distribution curve parameters.In this paper,the results respectively for three kinds of frequency adjustment i-t-P data tables,using least square method,marquardt method and surface search method for the fitting of rainfall intensity formula.On the same frequency adjustment curve,marquardt method error is least,ssurface search method is secong,least square error is the largest.Finally based on the error different theoretical distribution curve and parameter method through the comparison and analysis,using index distribution curve for frequency adjustment and marquardt method for solving parameters is the smallest error and the most reasonableis.In this paper,the Zhouzhi county rainstorm intensity formula is:When the return period is P = 2-20a,the absolute mean square error and relative mean square error are 0.0161 and 1.72%.When the return period is P=2~100a,the absolute mean square error and relative mean square error are 0.0213 and 1.68%.The error meet the specification required by the absolute mean square error is less than 0.05 mm/min and relative mean square error is less than 5%.In zhouzhi county during the design of drainage system,it is suggested that the return period for P= 2-20a rainstorm intensity formula.In flood control engineering design,it is recommended to use the return period for P=2-100a rainstorm intensity formula.This paper also given the zhouzhi county rainstorm intensity formula under the single return period,as a result of the integral formula precision is higher than the total accuracy of the formula.So when the return period of engineering design is same to the integral formula,we should choose the integral formula.