Simulation of Environmental Flow Assessment (EFA) Using XPSWMM for Enhancing River Ecosystem Sustainability in Kenyir Lake Basin

The study on Environmental Flow Values (E-Flow) found that existing river management practices could harm ecosystem health due to insufficient river flow rates. The main objectives of this study are to develop a hydrological model for hydrodynamics that determines E-Flow and to manage restoration and rehabilitation. Sampling activities commenced during both the dry and normal seasons, involving the collection of hydrology components, hydrodynamic data, and ecological samples. The giant snakehead fish species, Sebarau, and Belida were selected as bioindicator species out of the total 20 species of native fish sampled. Based on simulation, the 7Q20 low flow analysis for both study rivers determined that minimum river discharge values with the frequency probability over a 20-year period must be maintained in the Terengganu River. The optimal discharge is 42.78 m3/s, depth is 3.94 m, and water velocity is 0.54 m/s, all of which are anticipated to satisfy fish species development needs. Based on the simulation in the Petuang River, with an optimum discharge of 0.08 m3/s, a depth of 0.4 m, and a water velocity of 0.04 m/s, the river can only accommodate a few individuals of small-sized fish species. Both the lowest values obtained later were used as the input in low flow analysis, with an output error of less than 20% from the real situation. The uses and implications of the E-Flow are highlighted through the green physical structure proposed in assessing river health based on the Integrated Water Resources Management (IWRM) concept as a basis for maintaining optimum environmental flow level.