H&H is providing hydraulic analysis and preliminary design services for the Route 25A over Brackett Brook Bridge, an existing two-span reinforced concrete slab bridge in Orford, New Hampshire.
Previous DOT inspections revealed that the 1929 bridge was scour critical. The existing abutment and pier footings were exposed and one wing wall was undermined. Areas near the bridge experienced two flood events in 2017 that caused water to flow over the riverbanks and required emergency repairs to the adjacent road. Previous reports predicted a scour depth of 8 feet at the pier during a 100-year storm event. The Route 25A bridge needed to be either repaired or replaced.
Hardesty & Hanover performed an initial hydraulic investigation and structural evaluation to consider and compare the benefits of rehabilitation vs. replacement; ultimately concluding that a bridge replacement would be the most appropriate design solution. These findings were included in a Rehabilitation Study Report and concurred by NHDOT. The design team then performed a detailed HEC-RAS hydraulic and structural analysis, comparing the existing bridge with several Conceptual Alternatives to determine the most appropriate bridge replacement design. Hardesty & Hanover prepared a Type, Size, and Location (TS&L) Report, currently under review by NHDOT.
Hardesty & Hanover’s Part “A” contract, which includes this study and preliminary design, is still underway and is likely to be completed ahead of schedule. Future design includes scour analysis (HEC-18, HEC-20) and the design of scour countermeasures (HEC-23).