Tlogosari Kulon Village, Pedurungan District, Semarang City, is a densely populated residential area that regularly experiences inundation and flooding during high rainfall events due to increased surface runoff and suboptimal drainage system performance. This study aims to analyze the hydrological conditions, evaluate the capacity of the existing primary drainage channel, and determine its ability to accommodate the 10-year design flood discharge. The analysis used annual maximum daily rainfall data for 2015–2024 from three rainfall stations, namely Bodri Kuto, Karangroto, and Pucanggading, together with topographic data and field measurements of a 1,787 m-long primary drainage channel. Regional rainfall was estimated using the Thiessen Polygon method, while design flood discharge was determined through frequency analysis using the Gumbel distribution and the Rational Method. Channel capacity was evaluated using the Manning equation. The results indicate that the 10-year design flood discharge is 22.42 m³/s, whereas the existing channel, with a width of 7.50 m and height of 1.70 m, has a capacity of 36.08 m³/s and a flow velocity of 2.83 m/s. The capacity margin of 13.66 m³/s indicates that the channel retains sufficient hydraulic capacity under the 10-year design condition. The existing channel is hydraulically adequate, although periodic maintenance is required to control sedimentation, solid-waste accumulation, and channel narrowing.
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