Simulation Studies On LID Stormwater Planning Effect Of Qingxiushan Candle Bay Area In Nanning Based On SWMM

With the urbanization and traditional storm water management problems increasingly prominent, construction of Sponge City has become a hot issue in urban resource management about rain water. Qingxiushan known as the "Emerald Green City", is the demonstration area of Nanning urban ecological environment construction, and Candle Bay area belongs to the important partition of Qingxiushan scenic area. In order to study hydrological change before and after planning and development in Candle Bay area, and the reasonable rains’plan program combining with LID, the study using SWMM model respectively simulating rainfall about current program, general development program and LID program in candle Bay area, simulated results on hydrological changes of different programs and different sub-catchments is as follows:(1) Integrated runoff coefficient about current program, general development program and LID program in Candle Bay area are 0.217,0.378,0.265, meeting the requirement of development and construction of 0.5 or less; general development program runoff increase is 74.1%, LID program’s comprehensive runoff increase is 21.9%; runoff of the three programs are 2.608mm,4.54mm,3.18mm; evaporation are respectively 2.863mm,2.887mm,2.862mm; infiltration are 6.61mm,4.65mm, 6.011mm.(2) A common feature of hydrological state about the three programs’changes over time:they have the same trend runoff, runoff reaches the peak at about 55min, whose the shape of the change line is similar to rainfall, and the runoff always lags rainfall line; have the same trend infiltration; have the same trend evaporation. The difference is the range of variation:comparison with the peak runoff is general development program>LID program>current program; comparison with the infiltration is current program>LID program> general development program; during stably evaporating, evaporation of LID program is the minimum.(3) In three programs sub-catchment Sl-11, S14 the same as area have a common feature:comparison of the peak runoff, runoff coefficient and runoff is general development program>LID program.(4) In the same program, the runoff, evaporation, infiltration between the different sub-catchments have the same trend. However, the time when reach the runoff peak in each sub-catchment, the peak runoff, infiltration is different, relate with the underlying surface properties and impervious rate, but does not show significant change; change in the amount of evaporation in LID prgram is more obvious, the larger the area of LID measures, the smaller the amount of evaporation.By analyzing the results, the following conclusions:(1) General development program has affected the status of the natural hydrological cycle. From Candle Bay area as a whole or each sub-catchment, the hydrological state of LID program is closer to the status compared to a current program, LID program can reduce runoff, promote infiltration, reduce evaporation.(2) Comprehensive runoff coefficient of the three programs which are developed to meet the requirements of the building is 0.5 or less, but the runoff effect of LID program is superior to general development program.Generally speaking, LID program is reasonable and superior to general development program.