According to the Emergency Events Database (EM-DAT), more than 3,000 flood disasters were reported all around the world between 1992 and 2011. Those flood events were estimated to affect more than 2 billion people, and cause some 150,000 fatalities and economic losses around 480 billion USD. In terms of topographical data, 1-D modelling requires a certain number of cross- sections to represent the river channel and its surrounding topography. In this chapter, five hydraulic models of the Johor River with different spacing of cross-sections were developed: Jhr XS1, Jhr XS2, Jhr XS3, Jhr XS4 and Jhr XS5. All models include the reference cross-section at point X and point Y as well as the upper and lower cross-section used for upstream and downstream boundary condition. The differences between the estimation of the hazard area using different simulation case, highlights the uncertainty in determining an accurate estimating of the flood hazard area.