Storm Flood Simulation Based On SWMM Model And Effect Evaluation

The rapid expansion of the urbanization process has caused the problems of human and local contradictions.This destroys the original nature and ecological stability of the soil layer,leading to soil erosion,flood disasters and other problems.The concept of low-impact development of sponge city can maintain the stability of the hydrological circulation mechanism in the process of land development and protect the ecological environment.Taking the traditional construction site of Changan campus of Northwest University as an example,using SWMM model construction method,three most common low impact development facilities,such as green roof,permeable pavement,rainwater garden,simulated different combinations of three facilities,namely scheme one(water-permeable roof + green roof),Scheme 2(green roof + rainwater garden)and Scheme 3(permeable pavement + green roof + rainwater garden).Under different design rainfall conditions,the hydrological regulation effect of different schemes after site reconstruction is simulated.P=1a: the total rainwater emission reduction rate of Scheme 1(permeable shop + green roof),Scheme II(green roof + rainwater garden)and Scheme 3(permeable shop + green roof + rainwater garden)is 49.7%,54.3%,54.3%,65.4%,27.5%,20.3% and 34.4%;the peak delay time is 9min,8 min and 12 min.P=5a: the reduction rate of total rainwater emission in Scheme 1 to Scheme 3 is 46.2%,50.8% and 59.3%;the runoff coefficient reduction rate is 26.1%,19.7%and 30.4%;the peak delay time is 7 min,7 min and 9 min.P=10a: the reduction rate of total rainwater discharge in Scheme 1 to Scheme 3 is 44.3%,48.0% and 55.8%,the runoff coefficient reduction rate is 24.6%,19.1% and 30.1%,and the peak delay time is 2 min,4 min and 5 min.It can be seen that as the regulation effect of the same scheme is gradually weakened with the reproduction period;by increasing low impact development facilities for the site,the rainwater regulation effect of different facilities combinations increases significantly.From the comparison effect of each scheme,Scheme III(permeable pavement +green roof + rainwater garden)has the best reduction effect on total discharge and runoff coefficient.The test results further confirmed that the rainfall runoff control effect of the individual low impact development facilities was different,and the total rainwater emission control rate of the rainwater garden was better than the permeable pavement,while the runoff coefficient reduction rate effect of the permeability pavement was better than that of the rainwater garden.Hierarchical analysis method(AHP method)is widely used in the decision-making process of multi-target and multiple schemes.For the ecological,economic and social benefits evaluation of the above different facility combination schemes,the benefit analysis weight value of the AHP method model is calculated.The results show that in terms of ecological benefits,Scheme 3(permeable pavement + green roof + rainwater garden)is the optimal solution;in terms of economic benefits,Scheme 1(permeable paving + green roof)is the optimal solution;in terms of comprehensive benefits,The same scheme 3 is the optimal solution.The research method and test results have some reference value and guiding significance for guiding the allocation scheme of old urban-area sponge transformation and low impact development facilities in the process of urban renewal.