Analysis On The Stormwater Safety Area And Control Of Precipitation And Runoff For Sponge City Development

Sponge city construction is a new urbanization trend to improve the urban ecological environment and increase social benefits.Its purposes are to effectively promote the utilization of rain water resources and the protection of ecological environment.It realizes the accumulation,infiltration,purification and utilization of Rain Water in urban areas to the maximum extent.Sponge city is of great significance to the sustainable development of urban environment.In this paper,the daily rainfall data of Liaocheng City in recent 50years and remote sensing satellite images of Liaocheng City are used to analyze the present conditions of the construction of sponge city in Liaocheng City,by using the methods of long sequence method,typical years method and Analytic hierarchy process(AHP).The sensitivity of Rain Water and the safety zone of rain and flood in the city are discussed,and the runoff control objectives of sponge city construction in Liaocheng city are expounded.The main achievements of this paper were as following:(1)Liaocheng exists the necessity and urgency of developing sponge city.First,although rainfall over the past 51 years has shown no significant downward trend.The rainfall in Liaocheng is unevenly distributed in the seasons,with the rainfall mainly concentrated in summer and autumn,and the rainfall in spring and summer showed no significant increase.The incidence of moderate to heavy rain events,which account for a large proportion of rainfall throughout the year,tends to increase.Rainfall characteristics of Liaocheng City is one of the causes of Urban waterlogging.Secondly,the proportion of the construction land in the urban area is the largest,especially in the central and eastern part of the city formed impervious"non-sponge".With the development of construction land and traffic land,the increase of impermeable water in the city will also induce waterlogging.(2)According to Rain Water's sensitivity evaluation,Liaocheng urban area can be divided into drainage-based drainage area(Non-sponge area),infiltration-based seepage storage area(Semi-sponge area)and Storage-based and discharge-based regulating storage area(Sponge area).The sensitivity of Rain Water in the non-sponge area is 1~3.4.The non-spongy area should strengthen the connection with the storage area in order to drain Rain Water out in time,and improve the permeability of the non-sponge body to increase the amount of Rain Water collection for urban water use.The sensitivity of Rain Water in the semi-sponge area is 3.4~4.6.The semi-sponge body has a certain amount of water permeability.Due to the large agricultural water consumption,the semi-sponge area should give play to the regional water permeability advantage and form the infiltration-based seepage storage area.The sensitivity of Rain Water in the Sponge area re aches maximum of 4.6~8.304.The sponge area has more natural cavernous body,which should strengthen the protection of the area.The area has the best permeability,and the construction of reservoirs can increase Rain Water's storage capacity.Natural waterways provide conditions for the discharge of Rain Water in the city,and the arrangement of sponge measures in sponge area can play a better role in regulating and storing.(3)Under the present situation of land use,the comprehensive runoff coefficient is0.47,and control rate of annual mean runoff is 91.04%,so the annual rainfall of control is about 7.34×10~6m~3in Liaocheng city.75%of capture ratio of total runoff volume by long serial method is optimal combination of rainfall control and economic rationalization in Liaocheng City.Under this objective,Liaocheng will control the annual rainfall of 8.08×10~6m~3?Rainwater control target of sponge area,semi-sponge area and non-sponge area are2×10~5 m~3?2.07×10~5 m~3?3.33×10~5 m~3,respectively.After adopting four kinds of spongy urban construction measures of low elevation greenbelt,green roofs,Pervious Pavement and reservoirs,the rainfall collection will increase by 2.01×10~5m~3?2.63×10~5m~3?3.45×10~5 m~3,and expected Rain harvesting targets could to be met.