Evaluation of Flow Characteristics and Sedimentation in Urban Drainage Post Rehabilitation, Malang City

Abstract

This study evaluates the flow characteristics and sedimentation potential of the urban drainage system along Soekarno Hatta Street, Malang City, following rehabilitation measures based on hydraulic parameters. Rainfall data spanning from 2015 to 2024 were obtained from BMKG and analyzed using Hydrognomon version 4.0.3, with the Log-Normal distribution yielding the highest design rainfall of 130.268 mm for a 10 year return period. Hydraulic simulations were performed using EPA SWMM under two scenarios, namely existing conditions and post rehabilitation conditions incorporating vegetative swale application and channel dimension improvement to 2 m × 2 m. Simulation results under existing conditions revealed that conduits 41, 42, and 40 recorded maximum flow velocities of 27.25 m/s, 5.52 m/s, and 3.00 m/s respectively, exceeding the safe erosion threshold of 3 m/s, while conduits 19, 23, 25, 17, and 13 recorded velocities below 0.5 m/s, indicating sedimentation risk. Following rehabilitation, flow velocity reductions of 9.0%, 7.4%, and 2.8% were observed in erosion prone conduits, though all remained above the safe threshold. Among sedimentation prone conduits, conduit 19 showed improvement while conduits 23 and 25 experienced further velocity reductions, indicating increased sedimentation risk. The continuity error values of -0.05% and -0.12% confirmed model validity. These findings suggest that while rehabilitation positively influences drainage hydraulics, complementary interventions are necessary to fully address erosion and sedimentation risks.