Studies On Frequency Conversion Problem Of Short Duration Storm In The Main Cities Of The Province Of Fujian

In recent years, with the development of our country economic and the increase of the city area, the urban drainage design put forward higher requirement. The urban hydrology being the branch of the hydrology is recognised by people. Therefore, study on the urban design storm of the urban drainage engineering become one of the important problem prepared against and reduced disaster.Studies on the urban hydrology domestic and international have already made good progress, so urban drainage design is more scientific. Urban storm and storm intensity formula have been studied since the end of 70's or the beginning of 80's in our country. Its content is storm sampling method and parameter optimization method of storm intensity formula and storm intensity formula (including Fuzhou City, Xiamen City of the province of fujian). These researches are important to prepare against and reduce disaster and to improve city environment quality.Storm sampling method is often annual multisampling method in urban drainage engineering. But it is difficult to get the data of annual multisampling since 80 ages the sampling method of hydrology bureau is only annual maximum value. These problems need to be solved in urban drainage engineering. At the same time, with the accumulation of the data of annual maximum value from 60's to 90's, it provides the condition for the application of the maximum value. The data of annual maximum value gets easilier and can reduce workload and enhance efficiency. In recent years, a lot of scholars carry on studies to annual maximum method and obtain many results. Those results showed: the annual maximum method was feasible to being applied to the urban drainage engineering, but it didn't study systematically still. As well as short duration storm has the characteristic of region, there are different characteristics in different regions.Above-mentioned, this article analyzed and calculated the data from 49 rain observation posts of Fujian's 9 cities to look for the frequency conversion model between annual multisampling value and annual maximum value. There are four categories of storm sampling methods (annual maximum method and annual multisampling method and annual excess method and super-quantitative method). The frequency distribution model is p- III and Gumgel distribution and exponential distribution etc.. For the sake of the possibility of annual maximum method to replace annual multisampling method, we apply probability theory to built up four kinds of mathematics models. Year-frequency (1,2,3,4,5,10,15or20a) was transformed hypo-frequency according to four mathematics models. Storm design value was calculated from frequency curve of short-duration (5,10,15,20,30,45,60,90orl20mins). The error standard of assessment is criteria of sum ofabsolute value of deviations and criteria of sum of squares of deviations and criteria of NSE of the Nash- Sutcliffe. Then sum of absolute value of deviations and sum of squares of deviations and NSE were calculated in diffent short duration. Finally we can get mean value of sum of absolute value of deviations and mean value of sum of squares of deviations and mean value of NSE for 49 towns of Fujian' 9 cities. Results showed that: (1) the error is the least when the frequency conversion model 2 fits p-III; (2) p-III is the best fitting linetype and model 2 can be the frequency conversion model of short duration storm in the province of Fujian and can be applied to engineering design. The conclusion is useful to push studies on storm intensity formula in our country.