<![CDATA[Waterlogging along Cadika Road, Sintang Regency, West Kalimantan Province, indicates a problem in the urban drainage system caused by high rainfall intensity. This condition disrupts community activities, accelerates road infrastructure damage, and increases environmental risk. This study aims to analyze the design flood discharge, evaluate the capacity of the existing drainage channel, and redesign the channel dimensions so that it can effectively convey surface runoff. A quantitative descriptive approach was used, combining primary data from field observation of inundation and channel conditions with secondary data consisting of ten years (2016–2025) of daily maximum rainfall from the BMKG Tebelian Sintang station. Hydrological analysis was carried out using three frequency-distribution methods—Normal, Log Pearson Type III, and Gumbel—tested for goodness of fit using the Chi-Square and Smirnov-Kolmogorov tests. The Gumbel distribution was selected as the primary reference because its statistical parameters satisfied the theoretical criteria for extreme data, with a coefficient of variation (Cv) of 0.195, a coefficient of skewness (Cs) of 1.035 (≤ 1.139), and a coefficient of kurtosis (Ck) of 5.008 (≤ 5.400). Design flood discharge was calculated with the Rational Method, while channel capacity was analyzed using Manning's equation. Results show that the existing channel capacity cannot accommodate the design flood discharge for any return period. On the left side, the existing capacity is only 0.6932 m³/s, while the design flood discharges for the 2-, 5-, and 10-year return periods are 2.564, 3.177, and 3.582 m³/s, respectively; a similar deficit occurs on the right side. The channel dimensions were therefore redesigned to a width of 1.10 m and a depth of 1.20 m for both sides, increasing the capacity to 3.613 m³/s, which is sufficient to accommodate all design flood discharges (Qs > Qr). Keywords: channel capacity; drainage; flood; inundation; rainfall]]>
