Editor’s note: Aug. 5, 2024, 12:35 p.m. This story was updated to reflect that Debby was downgraded to a tropical storm status.
Savannah’s stormwater system performed a soggy dress rehearsal late last month for what looks to be Tropical Storm Debby’s arrival with “potentially historic rainfall” this week.
It didn’t go well.
Streets flooded in both the “usual” spots and in areas that caught residents and motorists by surprise. Emergency crews responded to about 50 stranded motorists and rising water damaged parked cars as nearly three inches of rain in an hour inundated neighborhoods including Avondale, Ardsley Park and the historic downtown.
For hard-hit areas it was a lot of rain in a short period, stormwater officials noted at a media briefing Friday.
“We’ve seen over the last week, numerous rainfall events that have been substantial in nature, inundating our city drainage system, sometimes with rainfall intensities on the order of three inches per hour, total rainfall of maybe five or six inches in certain areas of the city,” said Ron Feldner, Savannah’s Chief of Water Resources.
Clearing so much rain quickly proved a tough job for the city’s aging stormwater infrastructure, one that includes pipes so narrow — especially in the historic downtown — a bowling ball could plug them.
“It’s a challenge on normal days for us to handle extreme rainfall events,” Feldner said.
Savannah’s stormwater system, spread over about 115 square miles, includes more than 400 miles of pipes, more than 150 miles of ditches and canals, seven storm water pump stations, 31 tide gates, 14,000 catch basins, and 6,200 manholes.
(This video from Savannah explains how canals, tide gates and pump stations work.)
“So there’s a lot of infrastructure out there that we have to manage and maintain,” Feldner said.
The system can typically handle about 2 inches of rain an hour, said Zack Hoffman, director of stormwater management.
“We know that when we get intensity of greater than two inches per hour, when those rainfalls become that intense, our system, especially in the historic district of Savannah is undersized overall,” Hoffman said.
Tropical Storm Debby is forecast to bring 10-20 inches of rain over the week, with locally higher amounts approaching 30 inches north of Savannah, according to the National Weather Service in Charleston. The totals are also reminiscent of 2016’s Hurricane Matthew. During that storm, Hunter Army Airfield recorded 17 inches of rain in a 24-hour period.
When putting in new drainage, the city designs for 100-year storm events, or roughly 12 inches of rain in 24 hours, Hoffman and Feldner said. Savannah has more than $100 million-worth of new drainage projects in the works currently. See this Savannah Water Resources document for a list of drainage projects as well as list of areas prone to flooding.
July’s intense rainfall prompted targeted maintenance in Savannah, with crews focused on finding blockages, especially in areas that flooded unexpectedly.
“Obviously, last week really hammered home the importance of getting more boots on the ground, understanding where the system blockages are proactively,” Feldner said. “To clean, so to speak.”
The city expects to add to its maintenance staff the services of a contractor dedicated exclusively to storm drainage pipe inspection, Feldner said.
“So we can increase our capabilities of identifying maintenance needs, before the big rainfall event hits, not during or after,” Feldner said.
Crews use their three jet vacuum trucks to clear out the pipes then make sure it’s unblocked with a televising truck that snakes a camera through the system for a real-time look inside.
“And when I came across the crew around lunchtime, they had to jet vac truck out, they had the camera truck out, they were putting the camera down the line,” Feldner said on Friday. “They were trying to see if there any blockages in this flood-prone area. And the equipment was there to do the cleaning if in fact the camera noticed something.”
While those blockages are often leaves and other vegetation, that’s not always the case, Feldner said. He recounted a crew retrieving a bundle of newspapers blocking a drain. In July’s storm a metal disk was the culprit in a downtown pipe.
“That circular piece of metal was 10 inches in diameter,” he said. “And it was wedged up against inside of the drainage box, the 12-inch pipe that leaves the box. There was literally no flow there.”
It’s illegal to dump “letter, leaves, yard waste or chemicals” in storm drains.
“Even small amounts of debris can start to accumulate from an area and create a potential blockage, which of course creates street flooding and other types of issues,” Feldner said.
Residents can report flooded areas and blocked drains to the 311 system. Stormwater officials use the reports to prioritize their responses.
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