Crawley Falls Road Bridge

Brentwood, NH

Stephens Associates Consulting Engineers (SA) provided hydrologic, hydraulic and geotechnical engineering services for evaluation and design of repair or replacement of this single-span, reinforced concrete, rigid frame arch bridge originally constructed in 1941. The bridge provides the adjacent Brentwood Fire Department a critical access point across the Exeter River to portions of the Town.

During the major floods of May 2006 and April 2007 on the Exeter River, SA observed and photographed the flooding while it occurred, and subsequently aided the Town by observing sinkholes in the bridge deck created by the floods, and assisting the Town in applying for FEMA assistance. After the flood damage, the Town decided to rehabilitate or replace the Bridge to reduce the risk of further future damage and road closures, as well as to reduce maintenance and add life span to the crossing.

SA subsequently evaluated hydrology and hydraulics for the existing bridge and a wider proposed bridge opening. Using available data from FEMA, NHDOT, USGS, and the NOAA Northeast Regional Climate Center, SA evaluated flow, elevation, and water velocity of the 50- and 100-year floods. SA constructed a hydraulic model to estimate flood elevations and water velocities at the bridge, and calibrated the model with the flood data from nearby USGS stream gages and our observations of flooding from the 2006 and 2007 floods.

SA also performed subsurface explorations behind the bridge abutments and provided geotechnical design and construction recommendations for the proposed bridge. During construction, SA observed preparation of the bedrock subgrade at the abutment foundations for conformance with the design.