The Research Of Storm Intensity Formula In Li Country,gansu Province

Over the years,the frequent occurrence of extreme rainfall events in a number of areas in our country has caused great inconvenience to the operation of the city and the life of people,and poses a serious threat to the safety of people and the security of the property.This means that the planning and design of urban rainwater drainage systems must be promoted with better standards and more rigorous attitude in each regions,so that they can be improved and promoted.Therefore,the storm intensity formula,as the core gist of urban rain drainage system's planning and design has become the top priority of urban development.Moreover,as a city without the formula of rainstorm intensity,Li county more urgently needed the rainstorm intensity formulato guide the planning and design of rain drainage system in the area.The rainstorm intensity formula is an important basis for the design of rainwater design flow,urban rain drainage system design and planning,which directly affects the design planning of rainwater drainage project and the safety of urban rainwater drainage.However,due to various reasons,most cities in China for many years is to reuse the old formula of storm intensity,most of these formulas are derived from the obsolete data in 1970 s,and their usability and accuracy are not good,more middle and small cities(towns)even have never worked out a feasible rainstorm intensity formula,so that they must quote the rainstorm intensity formula of surrounding areas.Obviously,this is unreasonable and unscientific.It is very important to inquire into new rainstorm intensity formula for the dilemma which city faces heavy rain.The new rainstorm intensity formula is based on the more scientific and sufficient annual precipitation data of the city,and it is draw up by the latest national technical specification,which expresses the characteristics of urban rainstorm more objectively,and improves the scientificalness of the planning and design of urban outdoor drainage engineering.Based on the 29 years'new rainfall data which provided by the Meteorological Bureau of Li County in the year of 1986~2015,the annual maximum value method is selected as the selection method of rain samples for the formulation of storm intensity formula by comparing and analyzing the feasibility and scientificalness of the annual maximum value method and the non annual maximum value method.The frequency adjustment is determined to select the three commonly used theoretical distribution lines(including Pearson III type theory distribution line type,Gumbel type theory distribution line type and exponential type theory distribution line type),at the same time,the parameters of the three kinds of theoretical distribution curves are solved by using the line-fitting method and the least square method,so that three sets of i~t~P data tables and frequency fitting charts of the corresponding distribution lines are obtained.Then we optimize the i~t~P data under the three groups of different distribution lines,and the parameter optimization method is selected,including the least square method,the Marquardt method and the Gauss Newton method.Finally,the required parameters,absolute mean square error and relative mean square error of the total and integral formula of rainstorm intensity are obtained,in turn,the rainstorm intensity formula of Li county is determined.In the compilation process of the rainstorm intensity formula in Li County,the following conclusions are drawn by analysis and demonstration:a.and exponential distribution lines are the best distribution lines suitable for the Li County area;b.in terms of the same frequency adjustment distribution curve,the Levenberg-Marguardt method is the best fitting method,the Gauss Newton method is the next,the least square method is the worst;c.in terms of the error of the different distribution curves in different distribution curves,the error of the Levenberg-Marguardt method under the exponential distribution curve is minimal.It is determined that when the exponential distribution line is selected as the frequency adjustment method and the Marquardt method is selected as the method of reference,the formula of the rainstorm intensity will be most scientific and reasonable;d.integrated a,b,and c conclusion,selecting the rainstorm intensity formula which is obtained by the Marguardt method of exponential distribution curve as the final formula of rainstorm intensity in Li Country area.In this paper,the total formula of rainstorm intensity in Li country is:(?)?WhenP=2~20a,the absolute and relative mean square deviation is 0.0108 and 1.57%respectively,When P=2~100a,the absolute and relative mean square error is 0.0148 and 1.68%respectively.It shows that the derived formula is scientific and reasonable.According to the comprehensive analysis,in the LI country,it is suggested that the rainwater drainage system should adopt the rain intensity formula of the recurrence period P=2~20a,and the rain intensity formula of the recurrence period P=2~100a should be adopted in the design of the rain drainage system.In this paper,as the accuracy of the integral formula in the partially integral recurrence period is slightly higher than the accuracy of the total formula,therefore,Therefore,in engineering design,when the design recurrence period coincides with the formula recurrence period,it is recommended to use the rainstorm intensity formula which have the higher accuracy.