Analysis of time-varying law of flood designed by computer simulation during construction of sponge city: take Pingxiang City, Jiangxi Province as an example

Abstract

The time-varying law of design flood is the theoretical basis of sponge measure construction safety guarantee and measure effect evaluation. Based on the 2016-2018 rainfall and flood data in Wufeng River Basin in Pingxiang City, this paper uses the time-varying moment method to evaluate the time-varying process of flood designed by computer simulation. The analysis shows that the measured flood volume decreases linearly with time, the relative time difference between rain peak and flood peak increases with the logarithm of the time history, and the peak discharge firstly increases and then decreases with time. The optimal ratios of skewness coefficient and variation coefficient of total flood volume, peak discharge and relative peak current time difference are 2.5, 2 and 2 respectively, and the Nash coefficients between the element theory and empirical frequencies are 0.98, 0.79, and 0.93, respectively. After the transformation of the sponge city, the total amount of design floods decreased, and the total amount of once floods in the main flood season and the post-flood season from 4 to 100 years decreased by 16% and 8.5%. The relative time difference between rain peak and flood peak increased by 101.5% and 79.5% respectively in the main flood season and the post-flood season. The peak discharge during the main flood season increased by 4.8%, and then decreased by 9.5% during the post-flood season. This article can provides a scientific basis for the scientific and construction of sponge cities.