Both "Southern Alignment" bridge alternatives for the Knik Arm Crossing (KAC) are capable of altering flow patterns in their immediate vicinity, as well as altering processes of sediment transport (erosion and deposition) in Knik Arm. The objective of this hydrology study was to implement analytical methods that would address all reasonable environmental concerns and estimate quantitative changes potentially induced by each alternative. The environmental impact evaluation process addressed effects of potential alterations of the following hydrodynamic processes: Tide stage (water surface elevation [WSE]) and phase (timing); current velocities (maximum and mean values) beneath the bridge and both north and south of KAC alignment; sedimentation environment (erosion and deposition); effects of accelerated flows around bridge abutment ends.