HYDRAULIC MODELING FOR FLOOD CONTROL SCENARIOS IN AKELAKA WATERSHED, NORTH MALUKU, INDONESIA

Abstract

The Akelaka River experiences annual flooding, which inundates agricultural lands and settlements. The riverbanks of the Akelaka are relatively natural, covered with bushes and marsh grass. Given the site conditions, there are opportunities to combine ecohydraulics and structural flood control measures. Ecohydraulics flood control methods include reforestation upstream and planting vegetation along the riverbanks. Structural flood control methods encompass dredging, widening, diking, and creating retention ponds. The effectiveness of these treatments was evaluated using hydraulic modeling in HEC-RAS. The required data for this research included rainfall, terrain, land cover, site conditions, and technical plans for the proposed flood control measures. Results show that ecohydraulics flood control can reduce inundation by up to 32% for a 5-year return period and 39% for a 25-year return period. Retention ponds can reduce inundation by 47% and 50% for the 5-year and 25-year return periods, respectively. Dredging, widening, and diking nearly eliminate flood inundation for both the 5-year and 25-year return periods. While the structural approach (dredging, widening, diking) significantly reduces flood inundation, it may cause sedimentation and a decrease in the function of these structures over time. Therefore, combining ecohydraulics and structural flood control is the optimal strategy. Structural measures provide immediate relief from flooding, while ecohydraulics offer long-term sustainability. This recommended strategy has proven effective in reducing flood inundation, offering a reliable solution to the recurring flooding problem on the Akelaka River.