<![CDATA[This study evaluated the performance of the Terboyo Retention Pond in controlling urban flooding using a HEC-RAS 2D rain-on-grid simulation under a 10-year return-period rainfall scenario. Two comparable scenarios, without and with the retention pond, were assessed using four indicators: peak inundation depth, inundated area, inundation duration, and recession time. The results showed that the pond reduced peak inundation depth from 0.489 m to 0.465 m, equivalent to 4.91% effectiveness. Inundation duration decreased from 32 to 29 hours, while recession time improved from 30 to 27 hours, representing effectiveness values of 9.38% and 10.00%, respectively. However, the inundated area slightly increased from 13.25 ha to 13.31 ha, producing an effectiveness value of −0.44%. These findings indicate that the retention pond provides measurable temporal and depth-related benefits but does not uniformly reduce flood extent. The limited performance is associated with hydraulic bottlenecks in inlet conveyance and pumping capacity. Therefore, improving inlet efficiency, pump performance, and drainage connectivity is essential to enhance flood-control effectiveness in the Terboyo area. This assessment demonstrates the importance of evaluating storage infrastructure as an integrated hydraulic system.]]>
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