NHC assisted the Washington State Department of Transportation (WSDOT) in assessing the hydrologic, geomorphic, hydraulic, and scour aspects of the existing and proposed new US 101 Elwha River Bridge. The existing bridge was declared an emergency for repair or replacement after removal of the Elwha River dams caused the river channel at the bridge to lower by more than five feet. We developed a two-dimensional hydraulic model to gain a thorough understanding of the hydraulic characteristics and the risks of the existing US 101 bridge failing due to scour, assess a scour countermeasure design, and develop a design for a new proposed bridge. Seven alternative new bridge scenarios were developed by WSDOT and evaluated by a multidisciplinary team. The 2D model results were instrumental in supporting the environmental permitting process and in developing design parameters for the contractor to design a risk-based diversion for use during construction.