Study On Risk Assessment And Stormwater Management Of Xiangyang Central City

With the rapid promotion of urbanization,the construction of urban buildings,roads and impervious underground surface interferes with the runoff process of the original hydrological cycle,and the excessive rainwater that the urban pipe network cannot absorb makes the urban rainwater safety problem severe.The rainwater control combined with LID facility planning of the site is the only way to achieve green urban development.This study takes the central city of Xiangyang as the research object.Combined with the simulation of inundation range in the central urban area of Xiangyang,a stormwater risk assessment system was constructed,the stormwater risk priority areas were identified,and then the stormwater control effect was simulated for some stormwater risk priority areas through SWMM hydrological model,so as to propose the stormwater risk response strategies and measures to control stormwater risk priority areas of Xiangyang central urban area.The main conclusions are as follows:(1)Based on the combination of the SCS-CN rainfall-runoff model and GIS spatial simulation,the inundation process model under urban rainstorm events was constructed to delineate the inundation locations of stormwater in different rainfall recurrence periods,and the inundation area accounted for 18%,0.6%,0.7% and 0.3% of the study area,respectively.Under the condition of passive inundation,the simulated inundation ranges are mostly distributed in plane shape,mainly in local areas of the Hanjiang River,Xiaoqing River,and Tangbai River basins.Then,according to disaster-causing factors,disasterbearing environment,and disaster-bearing body,a storm flood risk assessment system was constructed.Seven index factors including inundation degree,precipitation,river network density,impervious water surface proportion,road network density,land use,and population distribution were selected to evaluate the storm flood risk in the central urban area of Xiangyang and identify different risk levels within the region.Different risk zones accounted for 9%,17%,35%,23%,and 16% of the study area,respectively.According to the assessment results,the main characteristics of the priority area of rain-flood risk were as follows: the space accounted for 9% of the study area;It is mainly distributed in the built-up areas of the city where the buildings are dense and the green space rate is low;it is relatively concentrated in the old city area of Fancheng.(2)According to the regional risk level,the priority area of site scale rainwater flood risk is identified,and the designed rainfall corresponding to the annual total runoff control rate is used to generate rainfall events in the small recurrence period.Then,the rain control effects of LID facilities under different scenarios are compared in terms of total runoff,peak runoff and runoff process.The results showed that in terms of total runoff control,compared with the current development model,the reduction rates of total runoff in the two scenarios were 69.33% and 94.84%,respectively,under the light rainfall event corresponding to the near-term target.Under the light rainfall event corresponding to the long-term target,the reduction rates of the total runoff in the two scenarios were 64.52%and 93.08%,respectively.In terms of peak runoff reduction,compared with the current development model,the peak flow reduction rates of the two scenarios are 71.8% and95.26%,respectively.Under the light rainfall event corresponding to the long-term target,the runoff reduction rates of the two scenarios were 65.17% and 94.49%,respectively.With the increase of rainfall in the recurrence period,the rain control effect of LID facilities gradually tends to be saturated,and the reduction effect of total runoff and peak flow decreases.By comparing the effect of rain water regulation in different scenarios,scenario B with LID facilities set in the optimal proportion has the best capacity of total runoff reduction and peak runoff reduction.(3)According to the comparison of the difference in the total control rate of rainwater runoff under different target scenarios,the results show that the rainwater control effect of using planning indicators to set LID facilities is significant,but there is still a certain distance between the near-term target of 65% of the total annual runoff control rate and the long-term target of 70%.In the design recurrence period corresponding to the short-term and long-term targets,the total runoff control rate of the scenario with the optimal proportion of LID facilities is only 2.68% and 3.8% lower than the 100% runoff control rate.Due to the variable situation of site runoff control under actual rainfall conditions,the control rate of LID facilities in the scenario with the optimal proportion is only 2.68% and3.8% lower than the 100% runoff control rate.Therefore,the short-term and long-term goals can be basically achieved by setting LID facilities in optimal proportion.