Flood policy evaluation, retention pond effectiveness in South Bandung

Indonesian cities use retention ponds to hold water and reduce floods. However, they rarely measure the ponds’ effects rigorously before building more at scale.

Cities often count completed ponds as evidence of success. However, that count gives weak evidence of reduced flooding. Rainfall, upstream changes, and expanding paved areas also affect flood rates. Therefore, a simple before-and-after comparison can credit ponds for changes caused elsewhere. City-wide policy needs evidence that separates the ponds’ effects from these other causes.

We used ProCANet to mark flooded areas and NDWI water-index maps across South Bandung catchments. Then, we paired these satellite results with policy document analysis. Together, they provided quantitative evidence of flood extent before and after pond construction.

The study translates satellite results for individual pixels into measures of policy outcomes. Therefore, city planners can use those measures to judge flood projects.