Assessment of low impact development (LID) strategies under different land uses in an urban sub-catchment in the Philippines.

Lack of studies in developing countries with tropical climate such as the Philippines limit local LID adoption. This study compared the performance of different LID scenarios across different urban land use types at the sub-catchment level using peak flow, runoff volume and flood reductions as performance criteria. Results showed that the most effective strategies for each land use are: 1) combined green roof and bioretention for low-density residential (reduction up to 10% peak flow, 11% runoff volume and 33% flood volume); 2) green roof for high-density residential (8% peak flow, 6% runoff volume and 18% flood volume); 3) combined rain barrel, bioretention and permeable pavement for industrial (23% peak flow, 41% runoff volume and 56% flood volume), and 4) combined vegetative swale and detention pond for urban open spaces (81% peak flow, 8% runoff volume and 84% flood volume). While effective for most low intensity storms, the observed sharp decrease in LID performance with increased rainfall intensity poses a major challenge, especially in the context of the Philippines frequented by high intensity storms. This study also examined how differences in land use characteristics influence LID performance, unlike most studies that focused on LID type comparisons. It showed that low urban density setting positively affected peak flow and flood reduction performance of rain barrels and green roofs, while good drainage infrastructure quality positively affected peak flow and flood reduction performance of rain barrels and bioretention. Decision-makers may use these findings to conduct rapid assessments on LID selection and siting, provided similarities between land use characteristics described in this study and those at their localities are justified. This can lead to increased LID adoption towards building water resilient, and sustainable cities.