Study On Hydrological Effect Of Low Impact Development Stormwater System For Residential Area In Mountainous City

The fate of precipitation for natural basin with permeable surface includes vegetation transpiration and interception, surface depression, infiltration and recharging groundwater and producing surface runoff into the receiving water. Urbanization makes the natural surface more impermeable and the drainage system change. So the hydrological mechanism is changed which is manifested in the change of water balance, surface runoff changes in size, time and frequency and the deterioration of water quality.In order to solve the problems caused by the hydrological effects of urbanization, the sponge city which mainly through the means of low impact development(LID is proposed formally by the Ministry of housing and urban rural development. The LID method has the characteristics of dispersion, small scale, sustainable and so on. In recent years, some technology in foreign countries has a wide range of engineering applications.This study takes Yorkshire of Yubei district as the research area. By using the method of field rainfall monitoring and storm water management model, the hydrological process of before urbanization conditions, after urbanization conditions(traditional rainwater pipe network), joining the LID facilities(low elevation greenbelt, permeable pavement and green roof) were analyzed, which is in order to assess the hydrological effects of urbanization, LID unit(a single type of LID facility) and LID combinations(combination of different types of LID facilities) respectively in the long duration typical rainfall and short duration of different return periods.Main results showed that:1) Surface impervious rates, surface runoff and peak flow were increased, time of runoff yield was shortened, and the formation time of the peak flow in advance, which puts forward higher request to the urban rain and flood control and drainage system. Low elevation greenbelt, permeable pavement and green roof can effectively intercept the rainfall runoff, reduce peak flows, delay peak time and ease the pressure of the flood; however the hydrological effects of them are different.2) Whether it is in the long period of typical rainfall or short duration of rainfall in different periods, the combination of LID can do better than three LID units in flood control, and it can effectively make up for the lack of LID unit in the rain flood control, make full use of plants to block the rain and make infiltration as soon as possible. It is in line with the concept of low impact development. In addition, with the comprehensive analysis of LID facility costs, LID is the optimal configuration.3) The LID model can improve the network flood control capacity. Although the cost of the initial construction is slightly higher than traditional technology, it can reduce the maintenance cost of the urban pipe network in the running stage and avoid the quantity of renovation and expansion pipeline project. Meanwhile, the LID model will have huge environmental, social and economic benefits.4) In the urban renewal process, LID technical measures should be actively adopted, such as the combination of low elevation greenbelt, permeable pavement and green roof. LID facilities should be combined with local actual rainfall condition, municipal drainage capacity and the standard of flood control and drainage. At the same time, the coordination between urban rainwater utilization system and other system is well done, and making the maximize using of rainwater sources.