Integrated Planning of Tidal Flood Gate for RT 22 & RT 12 Tanjung Limau Village, Muara Bada, East Kalimantan

Abstract

Tidal backwater and seasonal river surges from the Mahakam River have long posed a recurrent flooding threat to residents of RT 22 and RT 12 in Desa Tanjung Limau, Kecamatan Muara Badak, Kutai Kartanegara. To mitigate these impacts, a floodgate design project was commissioned in early 2025. This study aims to evaluate the technical, hydrological, and socio-environmental aspects of the proposed floodgate structure. A combination of hydrologic frequency analysis, hydraulic backwater modelling, structural dimensioning, and stakeholder consultation was employed. Rainfall frequency analysis was conducted using Gumbel, Haspers, Mononobe, Weduwen, and Nakayasu methods, resulting in a design discharge (Q₍₂₅₎) of 14.5 m³/s. One-dimensional HEC-RAS modelling was applied to simulate unsteady flow under tidal boundary conditions, revealing a peak water surface elevation of +7.06 meters. The selected structure—twin fibre-reinforced polymer (FRP) flap gates—was deemed optimal due to its resistance to corrosion and passive operation based on differential water head. Field surveys confirmed severe corrosion on the existing steel gate and sedimentation at the intake point. Stakeholder interviews showed that 86% of respondents expected the new structure to reduce operational costs by eliminating the need for frequent pumping. Project progress was aligned with the contract timeline, achieving 100% completion within 30 calendar days. No significant deviations were noted between planned and actual deliverables. Data visualisation highlights the reduction of inundation risk by approximately 78% upon gate installation. The project demonstrates a well-integrated planning approach involving hydrological rigor, stakeholder engagement, and structural resilience. Further recommendations include implementing a 12-month tidal monitoring programme and community-based gate maintenance protocols to enhance operational longevity. The study concludes that a cost-effective, site-specific, and environmentally adaptive solution is feasible and replicable in similar estuarine flood-prone settings. Kata kunci: pintu air, banjir rob, drainase pesisir, mitigasi banjir, Tanjung Limau.