Assessment of the hydrologic performance and cost efficiency of low impact development in a residential area in Cavite using stormwater management model (SWMM) and cost effectiveness analysis
Abstract/Summary
Low Impact Development (LID) is one of the current research interests toward green infrastructures and urban flood control that confronts the rampant urbanization and widespread use of impervious surfaces in the world today. LIDs have the capability to return developed watersheds to pre-development hydrological conditions, bringing numerous water quantity and quality benefits, while being cheaper than their traditional counterparts. In the Philippines, LIDs are currently not a well-known approach both in research and on a practical scale despite the country’s growing concerns regarding the constant flooding and deteriorating groundwater quality. This study assesses the suitability of various LID structures and scenarios in a residential park area in Cavite to determine their technical performance using Stormwater Management Model (SWMM) and their economic benefits through a life cycle cost evaluation. A cost-effectiveness assessment was performed using varying surface areas, rainfall, percentiles (80th, 90th, 95th, 99th), LID types (bioretention, infiltration trench, permeable pavement), and cost estimates (optimistic and pessimistic estimates) to determine the optimal scenario in the site area. The total rainfall estimated using the Weibull Plotting Position is 4.517mm for the 80th percentile, 16.64mm for the 90th percentile, 35.44mm for the 95th percentile, and 99.44mm for the 99th percentile. Upon comparing the different model types, it was observed that the decentralized models have better flow reductions than the centralized models, reaching more than a 60% percent difference. The integrated decentralized model performed best in most scenarios compared to the centralized model and land-use separated decentralized model. The optimal LID scenarios, as determined by the C/E analysis, have significant improvements to the water quantity aspects in the site. This can culminate in a 38.67% flow reduction, 29.73% peak flow reduction, 100% volume reduction, and 52.33% runoff reduction, which were all observed in the BR+IT+PP scenarios. At high rainfall amounts, the BR+IT+PP scenario can also peak at a 1,113% increase of total infiltration in the given sub-catchments. These reductions can lead to a pipe size reduction that can range from 0.1 to 16%. On the cost side, the capital cost comparison of a hypothetical traditional drainage and LID only scenario has shown that LIDs can yield cost savings that can range from 29 to 94%. The cumulative cost over two lifespans of the traditional drainage was also more expensive than most of the LID scenarios and can also yield cost savings that can range from 20 to 96%, depending on the scenario used. Determining the target capture goal, applicable LID types, and cost estimations from a pilot project are vital components in the future application of LIDs in the country.
