DETERMINATION OF ENVIRONMENTAL FLOW VALUES (E-FLOW) OF TERENGGANU RIVER AND PETUANG RIVER TO ECOSYSTEM SERVICE SUSTAINABILITY

Abstract
Kenyir Lake was built as a result of the construction of the Hydroelectric Dam in 1985, and this lake provides hundreds of river tributaries that supply water into the basin every day. The balance of environmental flow in the basin maintains ecosystems, biodiversity, and the environment. The requirement to maintain the optimum environmental flow for rivers is the necessity to ensure the sustainability of natural ecosystems. However, anthropogenic activities along the basin have affected the river ecosystems surrounding the lake areas. A study of environmental flow modelling in the Terengganu River and Petuang River aimed to ensure that the amount of river flow is sufficient to meet ecological and biodiversity needs. There are three objectives to be achieved, which are to identify the hydrology, hydrodynamics, and ecology characteristics of selected rivers, to develop a model of hydrology, hydrodynamics in determining Environmental Flow Values (E-Flow), and the management for restoration and rehabilitation based on the E-Flow in Kenyir Lake Basin. Sampling activities commenced during the dry season and normal season, involving the collection of three major components of the study, namely hydrology (observation of water level and river discharge parameters), hydrodynamic (XPSWMM software used) and ecology component (fish sampling and Length-Weight Relationship (LWR)) in each studied season). The study involved three sampling stations each selected in a different study river. Giant snakehead fish species (Channa micropeltes), Sebarau (Hampala macrolepidota), and Belida (Chitala lopis) were chosen as bioindicator species out of the total 20 species of native fish sampled, by taking the size (width, length, and weight) as selection factors for tolerance limits of E-Flow. The 7Q20 low flow analysis for both study of rivers found the minimum river discharge values with the frequency probability in 20 years needs to be maintained based on simulation in Terengganu River with optimum discharge of 42.78 m3/s, depth of 3.94 m, and water velocity as 0.54 m/s which are expected to meet the development needs of fish species. While, based on the simulation in Petuang River with optimum discharge as 0.08 m3/s, depth as 0.4 m, and water velocity as 0.04 m/s, which only accommodates a few individuals of small-sized fish species. Both the lowest values obtained later are being used as the input in low flow analysis, with an output error of less than 20% from the real situation. Based on individual fish captured and LWR analysis, it was found Terengganu River accommodates a higher diversity of native fish species compared Petuang River in both sampling seasons. The difference is that seasonal river discharges lead to deterioration of water quality in both rivers, with significant concentrations of Dissolved Oxygen (DO) and Total Suspended Solid (TSS) recorded the highest percent contribution compared to other parameters for Terengganu River and Petuang River. The uses and implications of the E-Flow are highlighted through the green physical structure proposed and a holistic assessment of river health based on the Integrated Water Resources Management (IWRM) concept, which serves as the basis for maintaining an optimum environmental flow level. Keywords - Environmental Flow Values (E-Flow), Terengganu River, Petuang River, Ecosystem Service Sustainability, XPSWMM software, Length-Weight Relationship (LWR)