A Study On Rainstorm Intensity Formula In Mian Country

Urban Storm Waterlogging has brought negative effects on people's life and even threatened the safety and developmenet of the cities in recent years.Rainstorm intensity formula is an important basis of design about the urban drainage engineering.So establishing the rainstorm intensity formula reflecting the local rainstorm regularity is an important prerequisite to ensure the healthy development of the urban.Many rainstorm intensity formula of big cities in our country were established in 1980 s,the rainstorm patterns have changed due to climate change and urbanization,so they can not adapt to the local drainage engineering well.In addition,some small and medium-sized towns without own rainstorm intensity formula.Usually they have to apply rainstorm intensity formula of neighboring city mechanically,which makes the safety and economy of the local drainage engineering to be studied.Mian county does not have the local rainstorm intensity formula,so it is necessary to compose the rainstorm intensity formula which reflects the characteristics of local rainstorm.This paper based on the original rainfall data,from 1996 to 2015 provided by Mian Meteorological Bureau,which use the annual maximum method to sample,and then the statistical data of rainfall are established.Three groups of i ~ t ~ P data tables were obtained through frequency adjustment by three kinds of frequency curves.And then use the least squares method,Marquardt method,Gauss Newton method to obtain rainstorm intensity formula.Finally,the best rainstorm intensity formula is selected by comparativing and analyzing the error of each formula and the the difference between the calculated value and the actual value.Based on the established statistical data of rainfall,three kinds of theoretical frequency curves were used to adjust the sample data then obtain 3 groups of i ~ t ~ P data table.By comparing the fitting error,we can find that The Gumbel distribution curve fits the data best,the Pearson ? type distribution curve is the second,and the index distribution curve is the worst.According to the 3 groups of i ~ t ~ P data table obtained by frequency adjustment,9 sets of storm intensity formula were obtained by using the above 3 methods,and the error was obtained.For the same distribution curve,the error of Least squares method is maxmum,the error of Marqardt-Hartley method is minimum.For the same optimization algorithm,the Gumbel distribution curve fits the data best,the index distribution curve is the second,and the the Pearson ? type distribution curve is the worst,which is inconsistent with the frequency adjustment results.Therefore,we should base on all the distribution model with different optimization algorithms to optimize the best frequency distribution curves by comparing the final fitting error.According the standard,five groups of rainstorm intensity formulas are selected,and then the difference between the calculated values and the measured values of the rainfall is calculated and compared.The formula of Mian county is (?)and (?).Combined with the scale of Mian city,the rain intensity formula(2 ~ 20a)is usually used in urban rainwater engineering;the formula(2 ~ 100a)used in urban waterlogging prevention and control works.The final rain intensity formula does not apply to urban water conservancy and flood control works.