FLOOD CONTROL USING RESERVOIRS (CASE STUDY OF THE BENGARIS RIVER, MUARA TEWEH CITY)

The Bengaris River is the longest river that passes through Muara Teweh. Heavy rain causes the Bengaris River to overflow, resulting in flooding. The objective of this research is to assess the capacity of the Bengaris River, design retention basin, and evaluate design effectiveness over a 20-year discharge return period at STA 4+248 (Pararawen II Street), STA 5+689 (Ronggolawe Street), and STA 6+049 (behind the BAPPEDALITBANG Office).This research purposes to calculate design rainfall using various distribution methods, including Normal, Normal Log, Gumbel, and Log Pearson III. Hourly rainfall intensity distribution using the Mononobe Method with 20-year return period. Civil Engineering software, HEC-HMS 4.10, designed discharge was calculated using several methods as Rational, Derweduwen, Haspers, Melchior, Snyder-Alexejev, Snyder, Nakayasu Synthetic Unit Hydrograph (HSS), and Soil Conservation Service Curve Number (SCS-CN) methods. HEC-RAS 6.0 model was used for river hydraulic analysis in both steady flow and unsteady flow simulations models.Two units are required to control water level of the Bengaris River at STA 4+248, STA 5+689, and STA 6+049 with the 20-year discharge return period, according to research findings. Reservoirs at STA 6+049 and STA 4+435 control storage quantities of 500 m3 and 800 m3, respectively. Simulation models showed a decrease in the wet cross-sectional area of the river at STA 4+248, from 112,030 m2 to 5.29 and STA 5+689 decreased from 51,950 m2 to 6.49 m2 (87.507%), whereas STA 6+049 decreased from 91.710 m2 to 3.91 m2 (95.737%).