Research On Integrated Technology Of Non-point Source Pollution And Flood Regulation In Mountain City

As the level of urbanization increases and the economy develops rapidly,the problem of urban rainwater is becoming more and more prominent.The main manifestations are:frequent flooding of urban rainwater;massive loss of rainwater resources;serious pollution of runoff,etc.Because of the complex terrain and many steep slopes,the rainfall peaks forward,rapid rainfall,short runoff collection time,the erosive effect of surface runoff is strong,the rainwater problem is more prominent,the sponge city construction involves different scientific and technological means than the plain cities.In response to the above problems,according to the actual situation of the topography,soil type,horological system,and runoff status of mountainous cities,we can optimize the process combination of various types of low-impact development（LID）facilities,and integrate a variety of sponge technologies according to the mountain situation,which can effectively realize the mountainous cities runoff pollution and rain flood control.In this paper,we study the effects of the integrated technologies on runoff water quality control and water quantity reduction in mountainous cities by continuously monitoring the operation of two sets of integrated technologies for surface source pollution and rainwater flood control（stepped artificial wetland integrated technology and rain garden-grass gully integrated technology）in the national sponge city construction pilot Yue Lai New Town Ecological Conservation Area,and obtain the best design parameters of the relevant technologies,which provide data support for the design of integrated technologies for storm water management in mountainous cities.（1）Analysis of runoff control effect and design parameters of stepped artificial wetland integration technology1)The peak reduction rate of integrated technology,total runoff reduction rate and flood peak delay all decrease with the increase of rainfall.For runoff with rainfall of 12.26mm,15.40 mm,22.69 mm and 57.33 mm,Total runoff reduction rate were 82.67%,67.76%,58.15%,51.32%;The greater the volume of the terraced wetlands,the greater the rate of total runoff reduction and peak reduction rate.For the terraced wetlands with a volume of 105m3,123m3,146m3,and 240m3,the average runoff reduction rates are11.81%,13.66%,and 15.36%,27.12%;2)With the increase of rainfall,the EMC reduction rate of each pollutant decreases,and the NH₄⁺-N,TN,TP,COD concentration of the effluent meets the surface IV water standard;the EMC reduction rate of pollutants of integrated technology decreases along the way,a step The field wetland has a better EMC reduction effect on each pollutant,and the average EMC reduction rate is 36.92%;When the service area ratio is 1:12,the best hydraulic retention time of the first-step,second-step,third-step,and fourth-step field wetlands is 0.15～0.67 d,0.16～0.56 d,0.73～1.07 d,1.59～2.53 d;If integrated technology is used to deal with low-concentration rainwater runoff,it is more appropriate to set up 3 to 4 terraced wetlands.（2）Analysis of runoff control effect and design parameters of integrated technology of rainwater garden-planting grass ditch1)The peak reduction rate of grass swale and the total runoff reduction rate decrease with the increase of the longitudinal slope;if the total runoff reduction rate of this section of grass-planting ditch reaches 80-85%,the required The length of the planting ditch is89.81～95.81m;2)The integrated technology’s EMC reduction rate for each pollutant decreases with increasing rainfall,and its treatment effect on SS is very significant.Under different rainfall conditions,the average value of SS EMC reduction rate is about 80%;When the service area ratio is 1:12,the best hydraulic retention time of the first-step,second-step,third-step,and fourth-step field wetlands is 0.15～0.67 d,0.16～0.56 d,0.73～1.07 d,1.59～2.53 d.