Regulation Capacity Evaluation of the Drainage System with Low Impact Development at a Watershed Scale in China

In the progress of urbanization, the natural permeable underlying surface is transformed into impervious underlying surface, which increases the surface runoff. Meanwhile, the overland flow is transformed into pipe flow with the construction of drainage system, which artificially organizes the confluence process. In order to reduce the impact of urbanization construction, the idea of low impact development (LID) has been widely recognized, which emphasizes the infiltration and storage functions of urban underlying surface through green facility construction. Runoff reduction effect of LID has been widely studied, but there is a lack of research on the runoff regulation capacity of drainage system in the LID construction region. We used a case study watershed in Beijing, China, in which LID facilities are widely implemented. The drainage system in this watershed is about two-year return period, the pipe network density is 5.90 km/km(2), and the storage volume is 12.6 thousand m(3)/km(2) (equals to 12.6 mm depth of runoff). Through the simulation analysis of Storm Water Management Model (SWMM), it can be found that before the implementation of LID practices, the drainage system can reduce the total and peak of surface runoff by 31.2% and 60.8%, respectively. And along with the increase of rainfall return period, the reduction effect of total volume decreased from 41.7% to 17.3%, while the reduction effect of peak flow had a slow upward trend. After LID construction, the reduction effect of total and peak flow changed to 34.3% and 56.9%, respectively. This study provides an insight into the regulation capacity of the drainage system in a LID construction region, which can expand the knowledge of urban stormwater management and LID evaluation.