St. Pete eyes rain gardens, reefs for flood protection

Along the shoreline at Maximo Park, clusters of concrete oyster balls offer a glimpse at how St. Petersburg could rethink its approach to flooding.

The artificial reefs break up wave energy and help slow erosion. City officials are now considering whether projects like that, along with rain gardens, bioswales, living shorelines and strategically planted trees, should become a routine part of how St. Petersburg builds roads, drainage systems and other public infrastructure.

The goal is not to replace the pipes, pumps and other traditional systems tasked with keeping a low-lying coastal city dry. Officials are looking at where natural features could supplement them.

“You can see where there’s not oyster ball reefs and you can see the water actually coming in, we’re actually losing land in that area,” Sustainability and Resilience Director Maeven Rogers said during a City Council committee meeting Thursday. “And you can see where the oyster ball reef construction actually held on to that land.”

Councilmember Richie Floyd requested the discussion, initially asking the city to put in writing that natural and ecological approaches should be considered when soliciting projects involving stormwater and storm surge.

City staff came to Thursday’s Health, Energy, Resilience and Sustainability Committee meeting without a proposed policy.

Rogers said developing one within roughly a month proved difficult because the appropriate approach can vary by geography, drainage conditions, existing development and vegetation.

There are also limits to how much water green infrastructure can handle.

St. Petersburg’s flood mitigation drainage design standard is 7.5 inches of rain over 24 hours. Green infrastructure generally targets closer to the first 1 to 1.5 inches.

That difference became apparent during intense rainfall in 2024. One storm unrelated to a named tropical system dropped rain at rates of 3.8 to 5 inches per hour over parts of the city, flooding at least 11 intersections and numerous homes.

“If we judge every green infrastructure investment whether it can manage that rainfall event or stop a major storm surge … we will have defined success in a way that almost guarantees failure,” Rogers said.

Green infrastructure uses plants, soil and engineered natural features to capture runoff where it falls. That can include rain gardens, tree trenches, green roofs, permeable pavement, bioswales and constructed wetlands.

St. Petersburg is already testing some of those approaches.

As part of stormwater improvements near Seventh Street and 50th Avenue N., the city is installing landscaped catchment areas designed to pull nutrients from runoff before the water enters the stormwater system and ultimately Tampa Bay.

The design also gives vegetation more soil in which to grow rather than confining trees and plants to small openings surrounded by pavement. Staff plans to monitor the project before deciding whether similar designs could work elsewhere.

“This type of solution is context-appropriate where the groundwater condition is good and where we do have enough volume of fluid to actually sustain the landscaping itself,” said Brejesh Prayman, the city’s Director of Engineering & Capital Improvements.

Other Florida cities already use similar systems.

Tampa’s El Prado project uses vegetation, engineered soils, gravel storage and drainage systems to capture and filter runoff.

Miami Beach paired a living shoreline with structural improvements at its Brittany Bay Park to reduce erosion, improve water quality and provide added protection from storms and flooding. The Florida Department of Environmental Protection also maintains a database of public living shoreline projects around the state.

Space is another constraint in St. Petersburg.

Staff cited Florida modeling showing dense mangrove forests can reduce storm surge by roughly 25 to 32 inches for every mile of forest width. The widest mangrove area staff identified in northeast St. Petersburg is about seven-tenths of a mile, and roughly 85% of the city’s shoreline is privately owned.

Expanding those buffers significantly could require acquiring developed waterfront property.

Maintenance also presents problems.

Rogers said the city already has locations where it could plant more trees but does not have enough labor to water and maintain them. Green infrastructure installed in the wrong location can also collect trash or create additional maintenance demands.

Council members focused Thursday on making consideration of those options part of the city’s normal planning process rather than prescribing a particular type of project.

Councilmember Gina Driscoll said she wants departments to ask whether green infrastructure could be incorporated from the beginning.

She pointed to a recent road project that included small patches of green space. Driscoll asked whether some could function as bioswales, but said she did not believe the idea would have surfaced otherwise.

“I would love for all of our departments to be thinking about that first and incorporate that into all projects,” Driscoll said. “Can we? And what would the options be?”

Staff plans to continue developing a citywide framework involving multiple departments and potentially residents and outside experts.

Rogers said the goal is not to build a natural system capable of stopping the next hurricane. It is to find smaller opportunities as streets, shorelines and drainage systems are rebuilt.

“If we can start looking at green infrastructure as one street, one garden, one shoreline, one tree at a time and then another,” Rogers said, “then that’s how we start to really work towards a city-wide green infrastructure policy where our residents can see it in the design and planning.”