Hydrodynamic modelling is a prominent tool for flood hazard studies to identify high flood-risk areas in communities, increase public safety, and reduce future flood-related damages. In this study, a one-dimensional hydrodynamic HEC-RAS model has been developed along 46 km of the Red Deer River, 32 km of the Little Red Deer River, and 33 km of the Medicine River, located in Red Deer County, Alberta. Model geometry was developed using surveyed channel cross sections and hydraulic structure data in combination with high-resolution LiDAR data. The model was calibrated and validated to the 1990, 2005, and 2013 flood events using highwater marks. Three statistical criteria, namely Root Mean Square error, Coefficient of Determination, and Nash–Sutcliffe Efficiency, have been used to measure the goodness-of-fit between the observed and simulated water levels. A reasonable agreement between the observed and simulated water levels has been found. The calibrated model result will be helpful to produce flood hazard and flood inundation maps for the study area. The paper demonstrated the importance of appropriate selection of ineffective flow areas, Manning roughness coefficients, and multiple opening bridge analysis in modelling the complex flow patterns near the hydraulic structures and meanders accurately.