Northstar Hydro, Inc. worked with Stantec and the Maine Dept. of Transportation on the replacement of several bridges on the Presumpscot River in downtown Westbrook, Maine. Northstar provided hydrologic, hydraulic and scour engineering services in association with the replacement of the twin Cumberland Street Bridges and the Bridge Street Bridge. The Cumberland Street twin bridges are located directly upstream of the Sappi Mill dams, fishway and production buildings. Both the dams and the buildings affect flood waters downstream of the twin bridges. Hydraulic modeling required detailed understanding of flow through the complex mill dam system and buildings.