Modelling a Sediment Excluder in Irrigation Canals: A Case Study of the Koya Tami Irrigation Area, Jayapura

The Indonesian Irrigation Design Criteria (KP-02 and KP-04) provide limited guidance for cohesive sediment at irrigation intakes. This study investigates a modified four-channel silt settler using field observations from Warujayeng and Koya Tami Irrigation Area, Jayapura. The assessment combines sediment analyses, HEC-RAS 2D modelling, FLOW-3D Hydro simulations of two alternatives at settling and flushing discharges of 5.0 and 7.5 m3/s, respectively, and hydraulic tests using a 1:5 physical model. Warujayeng downstream samples contained 74.59–75.01% silt and 20.97–21.79% clay, while cohesive fractions at Koya Tami reached 77–100%. Without baffles, settling opportunity indices were 0.48% for Alternative 2A and 0.02% for Alternative 2B, with surface loading rates of 2.19–8.14 m/h. Inlet baffles reduced the coefficient of variation in simulated channel-load distribution from 1.474 to 0.297–0.331. The projected settling opportunity index of 56.4–58.0% is an exploratory upper-bound estimate, not validated trapping efficiency. Full-gate-opening flushing removed 248.4 t and used 6.3% less water per kilogram of sediment removed than one-gate opening. Hydraulic validation yielded relative mean absolute errors of 6.43% for water level and 12.50% for velocity. Further cohesive-sediment transport tests are required to validate trapping performance.