Water Environment Restoration Based On "Landscape Drainage" A Case Study In A Mountain City

In recent years,with the continuous expansion of urban built-up areas,the hydrological cycle of mountain cities has changed dramatically,which has brought great challenges to urban flood control and water environment management.This study takes a typical area of a mountain city as the research object.The current status of important river stream and water environment in this area were investigated and analyzed.And in this paper,a typical watershed with problems of landscape invasion,mixed flow of rain and sewage and poor water quality,is simulated,and its water composition and characteristics are analyzed.The existing water environment problems are comprehensively analyzed,and according to the concept of"landscape drainage"(that is,the process of introducing mountains and rivers into water bodies by building a system of collecting,draining and discharging mountains and rivers for the sake of drainage safety and eco-environment friendliness in mountain cities),the countermeasures of comprehensive management of water environment in this river are put forward.The main results are as follows:(1)After on-the-spot investigation,it is determined that there are 13 water systems in the study area,among which 3 have certain influence on the urban drainage system,the main intercepting pipes along the Yangtze River,the operation and discharge of sewage treatment plants and the water environment of the Yangtze River;There are 51waterlogging-prone spots,of which 14 are waterlogged in urban areas due to the influence of the confluence of mountains and rivers.(2)The water quality of different sections of the upper,middle and lower reaches of three key water systems in the study area was monitored respectively,and the water quality was qualitatively evaluated by pollution index method.The results show that the average comprehensive pollution index q_i(pollution grade)of the three river systems is1.45(heavy pollution),0.55(slight pollution)and 1.1(heavy pollution)respectively,which shows that ammonia nitrogen and total phosphorus exceed the standard,mainly due to the inflow of external water(rainwater and sewage)caused by incomplete sewage interception along the river and the mixed connection of rain and sewage in the pipe network.(3)The Xin’anjiang model is used to simulate the rainfall-runoff process of the most important and typical River 1 basin,and its flow composition and characteristics are analyzed.The results show that the flow in dry season is mainly composed of underground runoff and coastal sewage,and the average daily discharge is 11130m~3 and1530m~3;respectively.The river runoff in rainy season increases with the increase of rainfall.Through the corrected model,the river runoff under different rainfall can be accurately obtained,and then the basis is provided for waterlogging control,water quantity control and water environment control.(4)Based on the above water quantity,water quality and simulation results,the water environment management system of representative rivers based on the concept of"landscape drainage"is put forward,and an integrated water environment management system of mountain cities with"landscape drainage-sewage removal and diversion-ecological restoration-intelligent interception"is constructed,which can effectively alleviate the operation load of intercepting trunk pipes and sewage treatment plants and greatly improve the water ecological environment quality of the basin.