Raising the Floodwalls for PennDOT’s I-376 Bathtub
The “bathtub” section of Interstate 376 has been a concern of not only flooding, but public safety, for decades. The sunken section spans about 2,500 feet and sees the passage of 40,000–70,000 vehicles daily. The area of the Parkway Central passes through downtown Pittsburgh, alongside the Monongahela (Mon) wharf, adjacent to the Mon River. The only buffer between the wharf and the bathtub is an existing concrete barrier that was converted to a flood control wall. This wall was able to provide protection for the roadway for a period of time, but it’s unable to serve its purpose as weather patterns continue to change. During instances of severe weather the Mon River rises and floods the wharf, flooding the bathtub as well, affecting thousands of travelers in the westbound direction of the Parkway.
The existing floodwall and pump systems were built in 1985. The current infrastructure is able to prevent flooding of the Parkway Central when the Mon River reaches up to a 25-foot river stage elevation, but when water levels rise beyond 25 feet, there is no prevention method or quick fix. After a flood, it takes about 12 hours to pump out the water and clean the debris; this cleanup costs approximately $100,000 each time. The bathtub has been shut down due to high waters or flooding 17 times since the first floodwall was built in 1985—four times since 2018 alone. The inconvenience to travelers, the risk to public safety, the cost of resources, and the required time to pump out floodwaters and clean debris are all motivation to transform the notorious "bathtub" section of I-376.
PennDOT reevaluated how best to preserve its transportation infrastructure and the safety of travelers on I-376 and called on CDM Smith to scope out the floodwalls and supply efficient solutions to mitigate the flooding. With firsthand knowledge of the interstate and preexisting infrastructure, CDM Smith is adapting to new weather challenges to achieve a safe, resilient roadway for PennDOT.
The firm is lending support to PennDOT by raising the floodwall and will consider prefabricated materials, reducing the groundwater table by calculating the hydrostatic uplift pressure of the pavement, managing soil and groundwater and limiting ROW impacts during construction. The team will consult with PennDOT in deploying an updated early flood warning system, along with low-maintenance pumps.
The team is also considering the speed and impact on stakeholders while completing a project that impacts thousands of Parkway Central travelers. Routing traffic in the City of Pittsburgh away from the bathtub causes substantial congestion, increased emergency service provider response times, as well as safety concerns.
Together, PennDOT and CDM Smith are working together to shed the nickname “bathtub” and fortify a dryer section of the Parkway Central safe from Mon River flooding. Through raising the floodwall and improving response/maintenance times, both teams are collaborating to promote the safety of travelers on I-376 while saving flood-response resources for the City of Pittsburgh.