<![CDATA[The Juwana Rubber Dam has a water level difference of 2.95 m and a fluctuating spillway discharge, which may cause local scour downstream of the structure. Studies linking discharge variations to local scour at rubber dams, particularly on the Juwana River, remain limited. This study aims to estimate downstream local scour depth for several return periods, compare three empirical methods, and determine the optimum spillway discharge theoretically. Design floods were computed using the Nakayasu Synthetic Unit Hydrograph for return periods of 25, 50, and 100 years (136.73, 148.53, and 156.80 m³/s). Considering downstream flow velocity and hydraulic jump height, scour depth was estimated using the Lacey, Wu, and Veronese methods, and the optimum discharge was determined by linear programming (POM-QM velocity, jump height, and discharge constraints. Scour depth increased with return period in all methods: 5.255–5.500 m (Lacey), 1.876–2.042 m (Wu), and 3.061–3.343 m (Veronese), with optimum discharges of 141.238, 143.144, and 143.430 m³/s, respectively. The methods differ substantially; for the 25-year return period, Wu's scour depth is 64.30% smaller than Lacey's. Among the three methods compared, Wu gives the smallest estimate and Lacey the largest (most conservative). Because this study is not supported by field measurements, the accuracy of each method could not be assessed, and the results should be regarded as an estimated range requiring verification with downstream bathymetric data.]]>
