Abstract
Lake is a water source that has decreased its function and has damaged the ecosystem. The Mahakam cascade lake in the East Borneo-Indonesia consists of Jempang Lake, Semayang Lake, and Melintang Lake, which have the sedimentation problem caused by the land-use change. The sedimentation can cause floods in the Mahakam River. However, the Mahakam River that correlates with the Mahakam cascade lake cannot reduce the happened flood. This study intends to optimize flood reduction modeling of Mahakam Cascade Lake towards the Mahakam River in the Muara Kaman outlet. According to the optimization model, this research aims to simulate the flood reduction modeling due to the 3 discharge conditions: Q25, Q50, and Q100. The food reduction modeling uses the Linear Programming Model, and the model is built integrated due to the Cascade Lake. The methodology consists of a linear programming optimization model due to the 3 scenarios (Q25, Q50, and Q100). However, the analysis of the design flood uses the Nakayasu Synthetic Unit Hydrograph in the watershed and the Rational Method for the discharge in the lake. The capacity of Mahakam Cascade Lake due to the bathymetry data and AWLR is as follow: 1) Jempang Lake: 519,958,550.36 m3; 2) Melintang Lake: 696,012,192.74 m3; and 3) Semayang Lake: 1,195,593,435.86 m3. The optimization model result of flood reduction in the Muara Kaman is as follow: a) Scenario-1 (Q25): Qmuara Kaman = 32,729.80 m3/s; b) Scenario-2 (Q50): Qmuara kanam = 37,432.36 m3/s; and c) Scenario-3 (Q100): Qmuara kanam = 39,777.80 m3/s.