Hydrological Effect Assessment Of Low Impact Development For Urbanized Area Based On SWMM

Natural basin with permeable surface has good abilities of blocking rainwater,flood resistance, recharging groundwater, and water purification. With the accelerationof urbanization, the area and surface have a big change. Runoff coefficients, runoffvolume and peak flow are increased significantly, and groundwater recharge is reduced.Caused by unreasonable laying of storm sewer and regulation of natural river, the runoffvelocity in drainage network is speeded up and the river’s storage capacity is reduced,and so prone to waterlogging disasters. As the forefront of China’s reform and openingup, Shenzhen has a lot of ecological problems, such ass flood disasters, increased pointsource pollution, water shortages and so on.To avoid those problems during urbanization effectively, low-impact developmentphilosophy is considered. Compared with conventional storm water and flood controland utilization methods, the low impact development (LID) method has characteristicsof sustainment, decentralization and so on.By field monitoring and simulating with SWMM, this research compared stormwater runoff under both pre-and post-development conditions, and modeled three LIDcontrol alternatives (permeable pavement, sunken lawn and green roof) in GuangmingNew District of Shenzhen to investigate the process of urbanization on the hydrologicalimpact of LID measures and the different effects of rain and flood control. Results showed that:1) watershed peak flow and runoff coefficient was increased significantly, andtime of max occurrence became earlier after urbanization; permeablepavement, sunken lawn and green roof can effectively reduce peak flows andrunoff coefficient, and can be effective in relieving the pressure rainwaterdrainage network; however, they have obvious differences in hydrologicaleffects under different condition;Combination of them can do better in floodcontrol, and then increase the amount of rainwater resources utilization.2) No matter in which rainfall conditions, the combined effection of three LIDunits is the most obvious. It is in line with the the concept of low impactdevelopment that, it can control rainfall in the source with maximize using ofgreen plants, making infiltration as soon as possible and making full use ofplants to block the rain.3) The effection of LID facilities to pipe network shows not only on improvingthe flood control capacity, but also shows on the financial security. There isgreater contribution of eliminating the adjustment of pipeline specificationsand reducing the frequency of maintenance of pipelines.4) In the urban renewal process, LID facilities should be located based on actualconditions; the effection of improving storm sewer capacity is also related tointensity and volume of rainfall; using LID facility can reduce the pipe size toreduce economic consumption in low rainfall areas, and can improve floodcontrol capacity of the pipeline in areas of frequent rainfall.