Research On The Determination Method Of Urban Short-Duration Rainstorm Intensity Formula And Its Parameters

The drainage and water protection in cities relates to the national economy and the people's livelihood. But the premise to urban drainage is to know the rainstorm regular clearly and to find an applicable urban storm intensity formula. The storm intensity formula is an important basis for the planning and design of urban drainage system, and its accuracy affects urban infrastructure construction directly.The accuracy of the storm intensity formula relies on dependability of the rainstorm data and rationality of the statistical methods. In the study of urban storm intensity formula, frequency distribution curve type and its parameters were confirmed according to samples, which were selected from local self-recording rainstorm data, and then storm intensity to a specified return period was gotten. At the basic of storm intensity formula and corresponding return period, the type and parameters of a storm intensity formula were confirmed. The choose of samples and the type of the frequency distribution curve determine the dependability and rationality of i-t-T relation. The type of storm intensity formula influences the regularity of i-t-T relation which is educed by frequency distribution.It takes Nanjing as an example in this paper. First, the sampling methods of rain data in Nanjing was analyzed, then frequency distribution curve three common used in short duration rainstorm, which are Pearson type III, Gumbel distribution and exponential distribution were try to fit the selected data. Finally, three-parameter storm intensity formula was adopted. The parameters in the formula were calculated using several nonlinear parameter estimation methods. Through the comparison of the above-mentioned methods, the annual maximal method was chosen as the method for sampling storm data. Pearson type III was taken as the fitted curve, and Marqardt-Hartley method was used to estimate the parameters. Furthermore, when the plan return period was consistent with the return period in three-parameters storm intensity formula, it was suggested that the storm intensity was calculated by three-parameters storm intensity formula, For its higher precise than three-parameters storm intensity formula. The method of complying urban storm formula in Nanjing is applicable to other similar cities.