Flood Mitigation in the Birthplace of America: The Cohocksink Storm Flood Relief Project

The Cohocksink Sewer System, which serves the Northern Liberties and South Kensington sections of the City of Philadelphia, conveys stormwater from a 1,302 acre drainage area. These neighborhoods were built around the original creek which was encapsulated with an approximately 16 foot wide arch-shaped brick sewer in the 19th century as development increased. Properties were developed along what would have been the banks of the Cohocksink Creek. Since the creek was buried and out of sight, it wasn’t perceived to be an issue, or was considered acceptable given the limitations of the economy and construction practices at the time. After the sewer system was constructed, heavy rains would overwhelm the system causing catastrophic pipe failures and flooding. Eventually the original sewer was reinforced with gunite to maintain pipe integrity but it was still undersized. To minimize the effects of flooding of the now developed area, the sewer system is being expanded to increase conveyance capacity.