Using HEC-RAS and qual2e to assess Johor River water quality

Abstract

Johor River is a major raw water supplier for a highly populated region, Johor state as well as Singapore. Because of the development over the entire catchment, water quality has become a sensitive matter. For this reason, several studies have been carried out in order to investigate its affects on the environment. Computer simulation and Numerical model are considered as essential and powerful tools in water resources monitoring plan in decision-making process. HEC-RAS is integrated system software designed to perform one dimensional hydraulic calculation. It was used to estimate the hydraulic changes due to the hydrological alteration of Johor River in response to the change of river discharges and to calculate the sediment transport capacity. Also in this study, QUAL2E was used as the water quality modeling analysis tool. It is suitable for one-dimensional analysis with constant flow and it is applied to predict the water quality model for the Johor River. The model was used to simulate both dissolved oxygen (DO) and biological oxygen demand (BOD5) along the certain reach of the river. Data was collected from several stations along Johor River, ranging from Rantau Panjang till water treatment plant. Flow rates, depths, loads, dissolved oxygen, and length of the river were measured in the field. Moreover, biochemical oxygen demands concentrations and total suspended solid were measured in the libratory. Those entire databases were used to supply inputs to the two models. As first time the HEC-RAS has been used to model; and followed by QUAL2E for simulating water quality at Johor River. Also In order to assess the vegetation buffer strips’ performance, and because of the reducing of the light penetration, harmful algal blooms, decrease in dissolved oxygen, total suspended solid (TSS) was estimated. All parameters are compared to the Interim National Water Quality Standard (INWQS) provided by Department of Environment (DOE). From the finding, the average concentration of suspended solid was 17.97 mg/l. The trap efficiency for pollution load reduction by vegetation buffer strip was estimated 9.17 % and this value would be bigger during high discharges.