Ecohydrological Indicators and Environmental Flow Assessment (EFA) in the Inlet and Outlet Reaches of the Kenyir Lake Basin, Malaysia

The balance of environmental flow in basin-maintained ecosystems is crucial for sustaining biodiversity and the environment. Maintaining optimal environmental flow in rivers ensures the sustainability of natural ecosystems. An Environmental Flow Assessment (EFA) was conducted in the Terengganu River (outlet) and Petuang River (inlet) to assess whether river flow is sufficient to support ecological and biodiversity needs. The study aimed to develop a hydrological-hydrodynamic model to determine Environmental Flow Values (E-Flow) and to use ecohydrological indicators for restoration and rehabilitation in the Kenyir Lake basin. Sampling was carried out during both the dry and normal seasons. Data were collected on hydrology (water level and river discharge), hydrodynamics (using XPSWMM software), and ecology (fish sampling and Length-Weight Relationship (LWR)). Three sampling stations were selected on each river, with the fish species Toman (Channa micropeltes), Sebarau (Hampala macrolepidota), and Belida (Chitala lopis) chosen as bioindicators. These species were selected based on their size (width, length, and weight), which indicates their tolerance to Environmental Flow Values. A 7Q20 low-flow analysis revealed that in the Terengganu River, the optimum discharge was 42.78 m³/s, with a depth of 3.94 m and a water velocity of 0.54 m/s, supporting the needs of larger fish species. Meanwhile, the Petuang River's optimum discharge was 0.08 m³/s, with a depth of 0.4 m and a water velocity of 0.04 m/s, which could only accommodate small fish species. These low-flow values, with an error margin of less than 20%, were used as inputs in the low-flow analysis. The study highlights the importance of E-Flow in maintaining river health. This holistic assessment, based on Integrated Water Resources Management (IWRM), supports sustainable ecosystem management using green physical structures to optimize environmental flow.