<![CDATA[Sidokare Indah Housing, Sidoarjo Regency, still experiences temporary inundation during high-intensity rainfall, requiring an evaluation of the existing drainage system. This study evaluates the system based on design flood discharge, long-storage capacity, pump-house performance, and hydraulic capacity of the existing channels. Maximum annual daily rainfall data for 2016-2025 from Sidoarjo Rainfall Station were analyzed using Gumbel and Log Normal distributions and tested by Chi-Square. The selected 2-year Log Normal design rainfall was 107.79 mm. Effective rainfall was transformed into a design flood hydrograph using the Nakayasu Synthetic Unit Hydrograph and convolution. The resulting peak discharge was 5.901 m³/s at 1.10 h. The long storage has a geometric volume of 2,903.565 m³ and an effective available volume of 2,088.279 m³, while the existing pump house consists of two 0.35 m³/s pumps and one 0.20 m³/s pump, giving a total capacity of 0.90 m³/s. Pump routing shows that the storage reaches its maximum capacity and overflow occurs during the peak-flow period; total overflow is 23,010.322 m³ and the storage returns to empty at 7.40 h. Manning analysis also indicates that most upstream and middle channel sections do not fully convey the design discharge. The system therefore provides attenuation and gradual drainage but does not fully control the 2-year design flood, so improvements to pumping capacity, channel bottlenecks, operation, and maintenance are required.]]>
