Study On Key Technical Issues For Sponge City Construction In Changzhou

After more than 30 years of rapid development in China,the accumulated ecological and environmental problems have become increasingly apparent and have entered a period of high frequency.The national rivers and groundwater pollution and drinking water safety issues cannot be ignored.In some areas,heavy metals,soil pollution is getting worse.The country has frequent large-scale smog pollution weather.Since 2000,many large and medium-sized cities in China have experienced frequent urban floods.On average,more than 200 urban floods have occurred in different degrees every year.Cities such as Beijing and Wuhan are flooded after big rains,leading to serious loss of life and property.The traditional method of rainwater drainage has also become a challenge to academic community.In October 2014,the Ministry of Housing and Urban-Rural Development issued a technical guide for the construction of sponge cities,which played an important role in promoting the construction of the sponge city in China.Sponge city is a crossover construction concept that is related to the water environment and integrates different fields,sciences and departments.The urban water ecology and water environment problems faced by the cities are different.Changzhou is a typical city featuring plain river network——flat terrain,dense river network,sluggish water flow and poor water self-purification.Sponge city construction techniques in China are still not unified.Other cities' sponge city applications cannot be directly used in Changzhou and its own application still needs to be studied.Therefore,it is more realistic to study the Xinlong Business District in Changzhou as a trial case for sponge city construction,based on its local conditions,such as the natural geographical conditions,hydrogeological characteristics,water resources endowment status,rainfall patterns,water environmental protection and internal flood control requirements.This paper firstly analyzes the current conditions of Changzhou sponge construction.SWMM models are established considering Xinlong's current status,regular construction mode and low-impact development with the help of the ArcGIS technology and SWMM rain flood model simulation software.The following research results are achieved:(1)Considering that Changzhou is faced with problems in four aspects including water environment,water safety,water ecology and water resources,it is more in line with the urban development of Changzhou to put the emphasis on water quality improvement and total runoff reduction.(2)According to the rainwater flow process,the sponge facility is divided into three categories: source water reduction,midway transfer and end storage.The priority of various sponge facilities is proposed after studying the adaptation of the key technologies of the sponge facility: source water reduction > midway transfer > end storage.(3)Under the concept of sponge city,technique models of different land construction should be tailored and determined by the nature of land use,the underlying surface condition and soil characteristics,etc.(4)Looking into the rainwater flood simulation output in Xinlong Business District,the peak runoff increases with the rainfall intensity,the annual overall runoff control rate decreases with the rainfall intensity,and the water accumulation rate increases as the intensity increases.For the entire study area,construction objectives for the land whose total annual runoff control rate is more than 75% are:(1)the sponge green land rate and the permeable paving rate should be 60%?60% respectively.The green roof rates of residential and public buildings are 40% and 60% respectively;(2)the sponge green rate and permeable pavement rate of the existing land parcel renovation are 50% and 50% respectively;Construction objectives for the land whose runoff pollution reduction rate is 65% or more are:(1)the sponge green land rate and the permeable paving rate should be 40%?40% respectively.The green roof rates of residential and public buildings are 20% and 40% respectively;(2)the sponge green rate and permeable pavement rate of the existing land parcel renovation are 30% and 30% respectively;...