Constructed in 1923, the Arch Street Bridge (SR 2064) is a state-owned seven-span steel truss bridge that carries SR 2064 over the West Branch Susquehanna River between Duboistown and Williamsport. Due to structural deficiencies and substandard horizontal and vertical geometry, it will be replaced with a 12-span, concrete girder bridge approximately 40 feet upstream of the existing bridge. NTM Engineering conducted a detailed hydrologic and hydraulic study of the river in the vicinity of the proposed SR 2064 bridge for PennDOT District 3-0.
The West Branch Susquehanna River has a well-documented history of flooding. Five major flood control reservoirs are located upstream of the project, and flood control levees constructed by the U.S. Army Corps of Engineers run parallel to the river through the project area. A low head dam downstream of the bridge controls flow depth during non-flood stages, and a USGS stream gage at the downstream Market Street Bridge contains continuous peak flow data from 1889. A statistical analysis was performed with daily stream flow data to aid in the design of the temporary causeways that will be used to demolish the existing bridge and build the new one. The annual peak flow data was carefully studied and used to develop 100-year and design flood peak discharge rates.
NTM used the U.S. Army Corps of Engineers’ HEC-RAS program to perform a one-dimensional, steady flow hydraulic analysis of existing, proposed, and temporary construction conditions. NTM’s study concluded that the project would not increase 100-year flood elevations, and the hydraulic analysis of scour was critical to the design of the pier footings. Construction began in the summer of 2010.