Hydraulic Performance of a Sand Trap in the Flushing Period to Support the Maintenance of the Pengasih Irrigation Network, Indonesia

Sand traps, as the first barrier against sedimentation in irrigation networks, have an essential role in minimizing the sediments in the irrigation channels. A large number of deposits upstream of the weir triggered a decrease in the sand trap performance. Pengasih is one of the irrigation schemes included in the Progo-Opak-Serang River Basin (WS POS) and gets water supply from the Serang River through the Pengasih Weir. 38.17% of the WS POS area is included in critical land, with an erosion rate of 234.83 tons/ha/year. It is necessary to evaluate the performance of the Pengasih Weir sand trap during the flushing period. The study’s objectives were to construct a hydraulic model, develop an optimum modeling approach for sediment transport in the flushing period, and identify the performance regarding the discharge and duration of flushing in the sand trap. This study used 1-D mathematical modeling software, HEC-RAS 4.1.0. The primary data were the channel’s cross-section, observed water surface, measured discharge, sediment properties, and flushing duration. The hydraulic model was developed by calibration and validation, providing the validated Manning’s coefficient of 0.025. The modeling approach for the sediment transport in the flushing period was Laursen for transport function, Exner 5 for sorting method, and Ruby for falling velocity method. The optimum discharge and sand trap flushing duration were 2 m³/s and 315 minutes. The flushing mechanism is optimal, and the duration adjustment is required to achieve a more effective and efficient sand trap operation in the irrigation maintenance period.