Copyright © 2018 Authors. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. International Journal of Engineering & Technology, 7 (4.35) (2018) 880-884 International Journal of Engineering & Technology Website: www.sciencepubco.com/index.php/IJET Research paper One Dimensional Shallow Water Equation Streamflow Modeling using WASH123D Model H. Basri* 1,2 , L.M. Sidek 1,2 , D.S. Shih 3 , H.C. Lloyd 4 , W.H. Azad 2,5 , A.Z. Abdul Razad 6 1 Civil Engineering Department, College of Engineering, Universiti Tenaga Nasional, Malaysia 2 Sustainable Technology and Environment Group, Institute of Energy Infrastructure, Universiti Tenaga Nasional, Malaysia 3 Department of Civil Engineering, National Chung Hsing University, Taiwan 4 School of Engineering, Faculty of Science Engineering & Built Environment, Deakin University, Australia 5 Department of Irrigation & Drainage, Malaysia 6 TNB Research Sdn Bhd, Malaysia *Corresponding author E-mail:BHidayah@uniten.edu.my Abstract Reservoir inflow forecasting assists dam operator in reservoir operation by providing advance information on lake level. This paper discusses on the application of the physical-based numerical model to simulate one-dimensional channel network using WASH123D Model. The model was developed to simulate streamflow at two locations namely Sg Kejar and Sg Tiang, located in the Temengor catchment. The WASH123D model performed channel routing using shallow water equation. The model input data includes rainfall from 5 rainfall stations, river cross sections and simulated runoff data using SCS Method. Due to unavailable observed data, results com- parisons were performed using streamflow results obtained using InfoWorks RS Platform. The peak flow from simulation results at Sg Kejar & Sg Tiang Station is 152.6m 3 /s and 36.6m 3 /s. The analysis shows good agreement for both simulations with Nash-Sutcliffe Effi- ciency of 0.68 for Sg Kejar and 0.99 for Sg Tiang. It is suggested that model recalibration shall be made once there is enough water level data to enable more accurate representation of spatial heterogeneity in the catchment processes. Keywords: hydrological model, inflow forecasting, physical-based model, shallow water equation, WASH123D 1. Introduction In the last few decades water especially river management and restoration play an important role in the environment and thus, numerous works have been done in this applied research field [1]– [3]. The hydrological model often used for various water man- agement functions such as flood and reservoir inflow forecasting and other real-time operational applications [4]–[6]. Apart from that, the hydrological model also applicable for off-line applica- tion for design & planning. There are many available hydrological models and can be categorized into three main types which are, the transfer function (empirical black box), lumped conceptual and physically based models [7]. Characterization of rainfall-runoff models is made by a different level of complexity and data re- quirement [8]. The model selection criteria can be made based on the type of application, the catchment characteristics and the data availability, different spatial and temporal scales, and different model conceptualizations and parameterizations [9]. Nowadays, one of the concerns for hydrologists is natural inflows to reservoirs [10]. Reservoir inflow forecasting enables appropri- ate planning of reservoir operation. Furthermore, the advance information can assist dam operators in ensuring the dam is operated at the optimized condition while maintaining the safety of the dams. This information is also pertinent to reduce the flood risk at the downstream area by proper planning of water release from the reservoir during a high rainfall event. The reservoir in- flow forecasting incorporates catchment runoff process modeling, channel routing model, storage routing algorithm, and reservoir operating rules. WASH123D is a finite element numerical model designed to sim- ulate variably saturated, variable-density water flow, reactive chemical transport, and sediment transport in watershed systems [11].This model was used in this study due to its capability to simulate flow in various component systems or combinations of component systems of a watershed [12]–[15]. The model has been successfully used to perform flood routing analysis due to a typhoon in Yilan River, Taiwan [16].Additionally, the WASH123D model was also used to model overland flow simula- tions Huwei Science and Technology Park, Taiwan [17]. Another application of WASH123D model was a simulation of the typhoon-induced flood in Lanyang River basin, Taiwan [18]. However, currently, there is no literature found on the application of WASH123D for simulation of reservoir inflow forecasting in Malaysia. This study uses the WASH123D model to simulate inflow into Temengor Reservoir. The objective of this research project is to develop an inflow forecasting system for the Temengor reser- voir.According to [19], the inflow forecasting system provides most useful outputs including river elevations, reservoir water level and time of occurrence for peak discharges with lead times that are sufficient to initiate appropriate responses by dam owner and authorities.The information obtained from inflow forecasting also essential to minimize the risk of dam failure [20]. Further- more, advanced warning on dam failure enables more efficient