Western Avenue Bridge over Contoocook River

Henniker, NH

Stephens Associates Consulting Engineers (SA) evaluated hydrology and hydraulics of this 300-ft. long, two-span, truss-type structure constructed in 1933 to be replaced.

Our hydrologic evaluation included of a regression analysis of the USGS stream gage peak annual flow data using a statistical approach to estimate the 50- 100- and 500-year floods. SA evaluated changes in the predicted floods at the Bridge compared to FEMA predictions that were made prior to removal of an upstream dam.

Our hydraulic evaluation included estimates of 50- and 100-year flood elevations for proposed Bridge configurations consisting of 2 spans, 3 spans, and 4 spans and for changes in configuration of the Patterson Hill Road Bridge immediately downstream of the Western Avenue Bridge. SA prepared a report summarizing our hydrologic an hydraulic evaluation, and met with NHDOT to review the results.

SA evaluated scour depths and mechanisms for each of the proposed configurations using FHWA methods, consulted with our client on scour mitigation approaches, and reviewed design drawings.