| The case study for this thesis was in Pocatello, Idaho. The objective of this paper was to provide recommendations for culvert additions for reconnection of historical oxbows along the Portneuf River in South Pocatello. The reconnection of the oxbows will provide flood storage and mitigation. Another objective was to compare the results of a HEC-RAS 2-D surface water model with a combined 2-D and 3-D surface water model in FLOW-3D. Total hydrographs with return periods of 2, 5, 10, 25, and 100 were developed as the flood events and all were modeled in HEC-RAS. The 25-year return period hydrograph was used to compare FLOW-3D and HEC-RAS results. A 4ft inlet culvert is recommended with an upstream invert at an elevation of 4467 ft and the downstream invert was placed at 4466 ft. Four 1 ft culverts are recommended at the outlet. Three culverts placed at the maximum floodplain WSE of 4470.5 ft to act as emergency outlets. The culvert at the lower elevation was used as the main outlet culvert. This culvert was placed at an elevation of 4461 ft. Water surface elevations within FLOW-3D were lower than HEC-RAS by an average of 3.6ft. Velocities within FLOW-3D were higher than HEC-RAS by an average of 0.52 fps. Depths within FLOW-3D were than HEC-RAS by an average of 1.23 ft. Results produced from HEC-RAS were determined to be more reliable than those of FLOW-3D. Due to a volume loss of 12% the FLOW-3D results were considered unreliable and unsuccessful. Keywords: HEC-RAS (Hydrologic Engineering Center-River Analysis System) |