Urban stormwater runoff reduction through low impact development (LID) on a city-scale catchment: A case study on San Juan City, Philippines

As urbanization and development occur, the natural hydrolic cycle is affected. This is due to the change of land use and cover, making most of the lands impervious. With that, stormwater runoff tends to increase, resulting to occurrence of flooding and degrade the quality of water. To compensate for the negative effect of urbanization, low impact development (LID) is applied on the urban catchment. LID restores the natural way of managing storm water wherein it stores water or allow it to infiltrate into the ground instead of generating stormwater runoof that leads to flooding and adds up to the pollution problems. The researchers intend to determine the effect of applying retention and detention type of LID in terms of water quantity in the City of San Juan. In which, the group simulated the predevelopment state, and the current condition of the stormwater in the area, and 14 scenarios of the current condition having LID. These scenarios differ in LID types and percent of area covered. The simulation was done in EPA Stormwater Management Model (SWMM) where hydrologic information of the catchment was considered. The findings of the model show that applicaton of LID results to 0.35% to 47.65% reduction in runoff volume, 0.12% to 45.68% peak runoff reduction, 1 to 11 minutes of delay in runoff, and 0 to 1-hour delay in runoff peak. More so, different types of LID result to different LID effects, with rain barrel being the most applicable LID type to the area since most of its land use is for residential purpose. Also, the results indicate that the percent coverage of LID has a direct relationship with runoff volume reduction, peak runoff reduction, and delay in start of runoff