Study On Sponge Effect Of Combined Technology Of Grass-Planting Ditch And Bio-retention Pond In Urban Road Rainwater Drainage

With the deepening of China urbanization process,the mileage of urban road construction has continued to increase,and the surface hardening rate has gradually increased.However,in recent years,extreme weather has frequently occurred,and the treatment of a single road drainage facility is relatively overload.Urban roads are prone to problems such as surface gathered water and water pollution.This paper provides a new solution for improving the rainwater runoff and pollutant control performance of urban roads through the research on the combined technology of grass-planting ditch and bio-retention pond.This paper analyzes the current research status at home and abroad,including discussing the proposed process and construction method of sponge city because of the problem of urban rainwater,and introductions of relevant technologies,then comes up with the combination system solution of construct grass-planting ditch and bio-retention pond based on respective characteristics of them.This study takes a part of Furong Avenue in Xiangtan City as the experimental research sample,investigating and analyzing its green space soil and rainfall surface runoff,it is found that some green space’s soil infiltration performance is poor,which will result in road water-logging.And the concentration of several pollutants in surface runoff water is so high that the water pollution issues are avoidable.After analyzing the detection of green-land soil quality and runoff water quality in the study area,this research proposes to use a combination of grass ditch and a bio-retention pond to solve related problems.In order to enhance the effect of rainwater runoff control and pollutant removal in a targeted manner,the facility was optimized according to the actual situation,and a series of comparative experiments are conducted,comparing a single grass-planting ditch facility,a single bio-retention pond facility,and the combined system of the two with the original green-land effect.Based on the above experimental analysis,this paper verified through the comparative study that the combined system of grass-planting ditch and bio-retention pond has the most significant sponge effect in urban road rainwater drainage.The research results show that the reduction rate of the flow velocity of the combined system in the middle period of medium and large rainfall is 31.21%～59.33%,which is20.3%～51.33%higher than that of the planting ditch in the same period,7.57%～49.33%higher than that of the bio-retention pond in the same period,and higher than that of the original green space in the same period,with the rate of 13.94%～46.00%.The flow reduction rate of the combined system was 70.58%～97.02%,which was 27.46%～45.02%higher than that of the planting ditch in the same period,23.71%～47.05%higher than that of the bio-retention pond in the same period,and 16.88%～24.04%higher than that of the original green space in the same period.The control effect of the combined system is also slightly better than the other three groups under the rainstorm type conditions.For the control of rainwater runoff pollutants,the comprehensive treatment effect of the combined system is the best,and it won’t cause secondary pollution easily.It is determined that under the purification effect of the combined system,the turbidity of the original surface sewage drops to 51ntu,the p H is maintained at about 7.4,the final removal rate of total suspended solids,total phosphorus,ammonia-nitrogen and total organic carbon(UV₂₅₄)changes,respectively comes to 84.57%,96.19%,34.64%and 97.20%.