Research On Stormwater Characteristics And Stormwater Management Design In Mountain Park Sites

On the background that frequent urban waterlogging,shortage of water resources and vigorous sponge city building,mountain park sustainable stormwater management has been paid more and more attention.However,the sites in mountain park as important open spaces and stormwater management nodes have a lot of stormwater problems.In this paper,69 sites in 15 mountain parks in Chongqing are surveyed and the flow sources of the sites are analyzed.Based on the Chongqing rainfall design standard under the year runoff control rate of 85% in "Sponge City Construction Technology Guide",and test value of runoff coefficient of different slope green land in "Study on the Runoff Coefficient of Mountain Urban Greenland and Cement Road",each flow source of the sites are calculated and statistical analyzed.The mountain park sites can be divided into three categories according to the catchment composition.The stormwater characteristics and present stormwater problems are summarized based on the categories.Then combined with the theory of stormwater management and the basis of design practices,this paper discusses the landscape strategy and approach of stormwater management design in the mountain park sites,and draws the following conclusions:The stormwater characteristics of sites in the mountain park is affected by many factors such as the position,the surrounding terrain,the road and the pipe.All those reflected in the difference between the source type and the flow rate.There are three main sources of flow: site’s own runoff,the surrounding green land runoff,and the road/ pipe runoff.According to the difference of the proportion of these three sources of runoff,the sites in the mountain park can be divided into three types: the self-produced,the mixed,and the confluence.The self-produced’s catchment are mainly due to their own runoff,and the site area has a large influence on the total flow amount,besides the site area and the total flow are the largest among the three types.The current problem is that the channel drain lead to downstream runoff increasing and external fountain isolation make runoff process control impossible.Therefore,the stormwater management design of the self-produced should be focus on decreasing self-production drain and increasing external runoff introduction and acceptance.Pay attention to "flow source adjustment","runoff collection" and " runoff transmission and retention".To form a stormwater management system of scattered collection,scattered retention,and centralized storage.Consider the size of the site area,the original drainage slope and the layout of the elements to make a partition for the site.Adjust some pavement material and drainage slope based on the partition.And set up flow collection facilities combining with tree pools,lawn,green belts and some other elements.Set up retention pools combining with some low-lying lawn inside the block,also some buffer pools combining with the edge green beltnearby the introduction pipe end.Finally,translate the runoff into reservoirs or wet ponds for storage.The mixed has a average catchment composition,small and scattered runoff.The current problem is that channel drain and ignoring the accumulation and utilization of small and scattered runoff lead to a waste of water.Therefore,the stormwater management design of the mixed should be focus on collection and retention of small and scattered runoff,and making use of them in some specific cases.Pay attention to "runoff collection","runoff retention" and "runoff gathering and using".To form a stormwater management system of classification collection,scattered retention,and centralized storage and using.Set up buffer pools at the junction of the road / pipe and the site.Layout some runoff collection belts such as planting grass ditch in the edge of the site and set up retention pools at the low point of these belts.Besides,in the no water view or less than 4000 square sites case,the catchment may be retained in the buffer pools or retention pools for evaporation and infiltration,otherwise translate and gather the catchment for collection and using.The the confluence’s catchment are mainly due to the surrounding green land runoff,and especially the road / pipe runoff,which is mass.The site area is the smallest among the three types.The surrounding green land slopes are large and the runoff is large and fast.The current problem is that slop erosion and pipe drain overload.So the stormwater management design of the confluence should be focus on avoiding slop erosion and pipe drain overload.Pay attention to "flow source control","runoff retention" and "runoff reserving".To form a stormwater management system of centralized collection,centralized retention,external reserving.For those slopes below 20°,it is recommended that to bury infiltration pipe or scattered infiltration wells,or shape the terrain into platform.For those slopes between 20°to 40°,it is suggested to combine the inclined platform with cutoff grooves or the infiltration pipes.For those slopes more than 40°,it’s better to use “rockery”,“cliffs fall” to avoid erosion and create beauty.On the other hand,for those green lands which slope 5°-20°and the catchment area is more than 10 times over the site area,or slope 20°-40°and the catchment area is more than 8 times over the site area,it’s more emphasis to reduce flow on the slope.The pipe runoff should be upstream shunted at those nodes of pipeline intersection or nadir,which is close to the self-produced sites or ponds.And cascade buffer pools should be set to quickly accept and purify the pipe runoff.After all,the catchment is not recommended for local retention.If there is no reservoir in situ,the catchment could be translated into an external water body or reservoir.