About this Project
As a State scenic byway, New Castle Avenue was not only an important roadway in an historic area, it was also one of two access roads from Portsmouth to Newcastle. The roadway is supported by a 1,100 ft long seawall which was collapsing into the sea.
FST completed an alternative analysis using a decision matrix to narrow down the options and provide a design recommendation to the City of Portsmouth, including conceptual analysis on intersection design options, and utility relocation options with cost analyses. The project required a New Hampshire Site Specific Permit.
Owner: City of Portsmouth
Location: Portsmouth, NH
Highlights: The New Castle Avenue drainage system was designed to maintain flows into the salt marsh without concentrating flows and negatively affecting the environment. This was particularly challenging since half the existing runoff was sheet flow over the seawall.