Rapid urbanization in Tangerang has altered land use patterns, increasing flood risk in residential areas such as Anwa Residence. The existing drainage system, originally designed for a 10.10 ha catchment area, currently serves 22.16 ha, resulting in increased runoff and reduced hydraulic performance. This study evaluates hydrological changes and drainage system capacity using ArcGIS-based catchment delineation, drone-derived topographic data, rainfall analysis, and hydraulic modeling. The existing retention pond has a surface area of 1,386 m² and a storage capacity of 2,079 m³ (average depth 1.5 m), allowing it to accommodate only 22.15% of the total runoff volume under the 25-year design storm. To comply with the local zero-runoff policy, two eco-drainage improvement scenarios were evaluated. Hydraulic storage calculations show that deepening the pond to 6.77 m or expanding its area to 6,258 m² provides sufficient storage to accommodate 100% of the total runoff volume of 9,387 m³. The proposed design enables complete runoff retention, contributing to flood mitigation, groundwater recharge, and sustainable urban water management