Research On Low Impact Development Mode And Its Evaluation In Urban Residential Areas

With the rapid development of social economy,the deepening of urbanization,and the environment of the ecological environment and climate change,the problem of urban rainwater continues to appear.It is not uncommon for phenomena of "a rainstorm can create a new Venice" to occur in our cities.In 2014,the pilot project of the construction of a sponge city that was supported by the central government in China was focused on the Low Impact Development(LID)concept of rainwater management and nonpoint source pollution control.Its purpose was to build natural deposits and natural penetration and naturally purified hydro-elastic city.In most cities,urban residential areas occupy a large part of the city’s body.It is also the room for the most frequent and close interaction between people and cities.Perfecting the rainwater system in urban residential areas is very important to urban stormwater management,meanwhile it is the key to building a hydro-elastic city.Based on the low impact development concepts and measures at home and abroad,this article compares the characteristics of urban residential areas in China,LID application suitability,construction requirements,rainwater function,economy,and landscape effects,and selects suitable cities in China.The low impact development facilities and combination model of residential areas,together with the "dot,line,surface digestion unit" model for low-impact development in residential areas.The "dot,line and surface digestion unit" of the mixed-use residential area was applied to the deployment of low-impact development measures in a certain community in Sanya,and a rainwater model was established by a software named storm storm runoff management model(SWMM5.1)to explore the rain of LID.Flood management effectiveness.At the same time,according to the requirements of low-impact development and construction in China and the actual conditions,a comprehensive evaluation system and evaluation method for low impact development in urban residential areas shall be determined.Constructing an evaluation system from the aspects of rainwater management benefits,economic benefits,social and landscape benefits,technical performance,and sustainable benefits.Apply the uncertainty analytic hierarchy process to obtain the weight of each indicator.According to the actual situation of the study area,a comprehensive evaluation was conducted to construct evaluation criteria in order to provide scientific reference and stormwater management direction for low impact development and construction of urban residential areas in China.This article focuses on the following studies for low impact development in urban residential areas:(1)The problem of rainwater in urban residential areas in China is mainly concentrated on the level of non-structural measures such as policies,management,public awareness,and structural measures such as source control,path control,and terminal control.The single low impact development facilities applicable to urban residential areas in China include permeable paving,sunken green spaces,green roofs,rain gardens and rainwater pipes.According to the design principles to be followed in the stormwater control plan and the characteristics of residential areas in China,the residential areas are divided into determinants,perimeters,point groups,and hybrids.The overall design,green space design,and specific implementation on hard roads are proposed to the "dot,line,surface digestion unit" layout model,and provides a plan,elevation,conservation,and appropriate plant configuration for individual facilities.(2)Combine rainstorm intensity formulas of Chicago Rainfall and Sanya into rainfall process lines of 0.5yr,lyr,3yr,5yr,10yr,and r=0.4.Using SWMM 5.1 to analyze the use of "dot,line,surface digestion unit"in a community in Sanya.The control of hydrological and water quality before and after the low-impact development measures were laid out:In the five different return periods,the total amount of runoff of the rainwater system by the LID measures were 11.28mm,13.79mm,and 16.8mm,respectively.At 17.64mm and 18.01mm,the reduction rates were 42.18%,42.04%,39.53%,37.53%and 33.86%,respectively.With the increase of the return period,the total amount of runoff reduction increased accordingly,and the reduction rate gradually decreased.With the increase of the return period of rainfall,the peak flow rate gradually increased,and the peak reduction rates were 43.53%,41.90%,40.15%,39.87%,and 35.26%,respectively,and the reduction rate gradually decreased;as the return period of rainfall increased The LID measures have a significant effect on the reduction of total suspended particulate matter(TSS)and total nitrogen(TN)emissions.(3)Research and construction of rainwater management benefits(runoff reduction,flood peak reduction,flood peak delay,pollutant removal capacity,increase in greening rate,rainwater collection and utilization),economic benefits(construction cost,operation and maintenance costs,life cycle cost,Additional economic value of the site),social and landscape benefits(public satisfaction,community participation,rationality of landscape space layout,richness of landscape hierarchy,LID measures and other landscape connectivity,ecological environment optimization),technical performance,and sustainability benefits(Technology evaluation,overall technical operation effectiveness,technology maturity,technical operability,technical applicability,and long-term benefit monitoring mechanism)Evaluation system for 4 indicator layers and 22 criteria layers.(4)Integrate the Vague set theory with the comprehensive evaluation and analysis of the residential area,set up five evaluation grades:poor,fair,general,good and excellent:the comprehensive evaluation in the study area is good,and the degree of membership in the good and excellent is over 75%.It shows that the LID layout method of the "Point,Line,and Surface Digestion Unit" in the residential area is effective.Further analysis shows that the rainwater efficiency of the rainwater system in the study area is evaluated as good,the evaluation of economic benefits is general,the evaluation of social and landscape benefits is excellent,and the evaluation of technical performance and sustainability benefits is good.The study area has obvious effects in runoff reduction,flood peak abatement,and water quality management.At the same time,it can increase the participation of community residents in the healthy water cycle.However,due to the high investment costs and slow vegetation growth at the initial stage of construction,the site has additional economic value,peak runoff delay capability and long-term monitoring capability are not prominent.(5)According to the study of the study area,relevant regulations,policies,and case studies,detailed descriptions of poor,fair,general,good,and excellent evaluation criteria for each indicator are provided,it provides a certain amount of science for the construction of urban residential areas,avoids the blindness of low-impact development,provides designers with a feasible,accurate design direction and further improves the rainwater management efficiency of urban residential areas.