Study On Influence Of Snowfall On Typical LID Facilities Under Concept Of Sponge City

Since October 2014,the "Sponge City Construction Technical Guide-Low Impact Development of Rainwater System Construction" was published by the Ministry of Housing and Urban-Rural Development of China,30 cities had been selected as sponge city pilot cities by 2016.This program means to solve the frequent occurrence of urban diseases such as "watching the sea in the city".Although the goal of the construction of the Sponge City is to solve the problem of urban stormwater management,precipitation in northern China is reflected by snowfall in the winter,even the whole country.Unlike the cases of general rainfall,the impact of snowfall is reflected in the accumulation and melting stage of the snow.During the snow melting period,the snowmelt runoff is also one of the major factors which cause urban surface runoff.So far,there is no domestic study to explore the specific impact of winter snowfall on sponge city.Therefore,the purpose of this paper is to explore this issue to fill gaps in the study of sponge cities in snowfall environment and provide a kind of research method of Sponge City related with snow.Based on the relevant concepts of the sponge city and the specific theories of the snowfall and snowmelt process,this paper finds a research method that can use SWMM simulation software to simulate snowfall and snowmelt process in the environment of Sponge City.And through theoretical analysis,it is found that when using SWMM simulation software to simulate snowfall,it not only needs sufficient precipitation data and specific LID facility parameters,but also needs other elements such as temperature,wind speed,evaporation rate of snow,altitude,the snow-related parameters and snow treatment methods.This is different with the rainfall period which only needs the first two parameters.Through the simulation of each typical LID facility and a sponge-modified urban arterial road,it can be summarized as follows:(1)During the snow melting period,the change of temperature is the main factor which affects the simulation results.The specific effect is that the faster the temperature rises,the faster the melting of the snow melts.And the snowmelt runoff will have different effects on the different LID facilities.(2)When there is a rainfall condition during the snowmelt period,the magnitude of rainfall intensity directly affects the simulation results.Specifically,the rainfall results in the acceleration of the snowmelt rate,which results in a larger total runoff.This total runoff includes two kinds of runoff,snowmelt runoff and rain runoff.Under rainfall conditions,the altitude of the simulation process and the wind speed parameters has almost no effect on the simulation results.But if the input of these two parameters is ignored,the simulation results will have a non-negligible impact.(3)In the simulation of snowfall and snowmelt periods in a specific area of a sponge city,when there is no accurate local snow evaporation rate data,it is recommended to use the formula method based on the Hargreaves equation for the snow evaporation rate parameter.The selection of snow treatment methods for each sub-water catchment area or each parcel should also be reasonably conducted in accordance with the actual treatment method.Comparison found that the use of snow-melting agent for snow treatment in the snow treatment process has the largest impact on the simulation results.It is due to the snowmelt agent accelerating the melting process of snow,forming more snowmelt runoff in extreme time,and the amount of snowmelt runoff directly affects each simulation results.(4)The simulation show that if the snow-melting runoff is used for greening water,106,000 cubic meters of water will theoretically be produced,which generated during the winter of 2017-2018 in Urumqi,about one thousandth of the total annual ecological environment water consumption in Urumqi.