Hydraulics of the river mouth with a tidal effect intrusion is sometimes quite different from that of the river without them. Upstream and downstream interactions of any hydrological and hydraulic system or watershed are complex and elusive. The type of land use and land cover of the area would largely determine the magnitude and extent between upstream and downstream interactions and accordingly the degree of degradation to the environment. Because of these, it is usually difficult to measure the flow field in the river mouth by using the ordinary methods. In this study, Sungai Sengkuang is a re-aligned and straightened channel is under tidal influence. The hydrologic and hydraulic analysis has been carried out for the existing system to investigate whether it is still able to accommodate the volume of water comprises the discharge from upstream and high tide from downstream. The actual data such as rainfall data, velocity, water level, tide level has been collected for the analysis. HEC-HMS is used to carry out the hydrologic model calibration and validation. By using HEC-RAS, hydraulic model calibration and validation is carried out for the channel. The discharge from flow simulation and tide level from frequency analysis with different ARI are used as the upstream and downstream boundary condition during the steady flow analysis. The result show that the existing channel is still able to accommodate the flow from upstream and downstream but the cross section of channel needs to be improving because of inadequate freeboard. From the Energy Grade Line of the channel, it can be concluded that the energy from downstream is more dominant than the energy from upstream.