PennDOT ready to deal with chronic ‘bathtub’ flooding in Downtown Pittsburgh next year

The Pennsylvania Department of Transportation and its consultants have designed an estimated $34 million project to keep “the bathtub” dry most of the time and prevent the Monongahela River from overflowing onto the Parkway East in Downtown Pittsburgh.

Beginning after the National Football League draft in April next year, the department will reconstruct the flood wall along the Monongahela Wharf between Grant Street and the Fort Pitt Bridge. The project will increase the height of the flood wall by as much as 5 feet to reduce the amount of water that can block the roadway for 40,000 to 70,000 drivers a day.

PennDOT and consultant CDM Smith have designed a project that also will put a more extensive pumping system in place and drive micropiles into the road surface to make sure it stays intact while the water is being held back. The project should be completed by the end of 2026.

“I’m probably the happiest person in the district,” said Lori Musto, PennDOT’s assistant district executive for maintenance in Allegheny, Beaver and Lawrence counties whose team is responsible for operating the pumps and cleaning up after the bathtub floods.

“Last year, I think I cleaned that bathtub more than I cleaned my own.”

Flooding in the bathtub area has been a vexing problem over the decades, with CDM Smith reporting on its website 18 instances since the current flood wall and pumping system were installed in 1985. At least five of those floods have occurred since 2018 — two of them last spring — as weather patterns have changed.

The inbound Parkway East dips under ramps and bridges as it passes through Downtown Pittsburgh between Grant Street and the Fort Pitt Bridge. This creates an area to collect water — a bathtub — when the Monongahela Wharf floods at 18 feet, before rivers flood at the Point at 25 feet.

PennDOT and other officials were keeping a close watch on river levels Sunday after several days of rain closed the wharf to parking and threatened to keep rising with more light rain in the forecast.

This isn’t a problem for the outbound Parkway East because it passes through the city at street level, well above the wharf.

Every time the bathtub floods, it creates a traffic nightmare in Downtown Pittsburgh because all inbound traffic has to get off the Parkway East at Grant Street or earlier and weave its way through the Golden Triangle to make a different connection with the Fort Pitt or Fort Duquesne bridges. After the water stops rising, it takes PennDOT crews a minimum of 12 hours to pump out the water and haul away the mud and debris at an average cost of $100,000 each occurrence.

PennDOT has been looking at the problem and developing a solution for more than five years. In the past two years, it has received a pair of federal Department of Transportation grants worth $45.6 million to pay for the design and for construction that will go out for bids in September at an estimated cost of $34 million.

Over about 1,015 feet of the wall will be replaced with a new one that is 3 to 5 feet higher depending on the location between the wharf and the highway.

But the complicated process of protecting the roadway will involve much more than holding back a larger volume of water, said Doug Seeley, assistant district director for design.

Holding back more water will mean a substantial increase in hydrostatic pressure, a lateral force created by the weight of the water. If the agency doesn’t do additional work to stabilize the road on the other side of the wall, that pressure could cause the surface to heave substantially and create a long-term closure while it is rebuilt.

In preparing this project, Seeley said, designers found that the original flood project in the 1980s prepared for this situation. Ordinarily, a road has a surface and two sublayers under it.

“What’s unique with that pavement is there’s a significant foundation under the sublayers,” Seeley said.

Crews will dig out the top three layers of the roadway, Seeley said, then “keep as much as we can” of that foundation and drive dozens of steel micropiles through it to about 60 feet deep into bedrock. The micropiles, hollow and 7 inches in diameter, will be filled with grout to fortify the roadway so it can withstand the greater hydrostatic pressure created by the higher wall.

Then new sublayers and a new surface will be laid.

In addition, Musto said, the agency will install new, larger pumps that can be started remotely and new sluice gates that can be lowered electronically. Sluice gates are devices that are put in place to regulate or direct the flow of water.

The new system will allow work to begin before crews can arrive at the site, she said. Because of the volume of traffic in the area, the goal is to do most of the work with lane restrictions rather than closing the highway, Seeley said. Parking on the wharf will be reduced during construction.