At the edge of Florida's most densely populated county, wedged along the borders of Gulfport and St. Petersburg, ecologists and engineers are recreating a natural oasis.
Once an open-water estuary leading to Boca Ciega Bay, Clam Bayou had become the stormwater dump for 2,400 acres of highly urbanized neighborhoods. Sediment and trash clogged the narrow tidal channel that flowed past Osgood Point and pollutants from yards and parking lots were degrading water quality.
"The neighborhoods were built before state regulations required any kind of treatment for stormwater, so it was flowing into Clam Bayou basically untreated," said Brandt Henningsen, chief environmental scientist for the Southwest Florida Water Management District.
Restoring Clam Bayou with a series of interconnected water features and upland habitat has been a labor of love for the scientist who usually works on wide-open spaces like Cockroach Bay in southeastern Hillsborough County. "It's been challenging, but it's wonderful to see this kind of natural oasis in the midst of an urban area," he said.
It's also been a long-term project for Henningsen and the district's SWIM (Surface Water Improvement and Management) program. "We started in 1995 with the restoration of 10 acres in a partnership with the City of Gulfport and the Florida Department of Environmental Protection," he said.
That first section became the Clam Bayou Nature Park, which features an open-water lagoon rimmed by marshes and coves as well as coastal uplands that offer habitat for a wide variety of birds, fish and crabs. Marshes that line the shore were among the first ever planted by volunteers from Tampa Bay Watch. Tiny oak trees planted nearly 15 years ago now offer a shady refuge for visitors and gazebos overlook the lagoon that's become a favorite spot for kayakers paddling its protected waters.
"When we finished it, a local resident approached us and asked why we couldn't do more," Henningsen said. Looking for suitable land and the funding to purchase it took a few years, but construction began on a second 10-acre parcel in 1999 in a partnership with the City of St. Petersburg.
Once planned for development as a second phase of the West Shore Village condominium at the end of 34th Avenue South, the land had been cleared and utilities installed. As it sat empty, invasive plants including Brazilian peppers, Australian pines and lead trees quickly became an impenetrable forest destroying whatever wildlife habitat might have been left. Drainage from nearby neighborhoods was washing through the property before it was dumped into Clam Bayou.
Rather than focusing on recreational opportunities, the second phase emphasizes stormwater treatment with innovative channels and weirs that capture stormwater and force it through a series of lagoons and channels to capture trash and contaminants before it overflows into the bayou.
The third and final phase, scheduled for completion later this year, is the largest and most challenging. Seven distinct sites include 20 acres of water treatment areas and 24 acres of upland habitat. "The lagoons are all linked by overflow weirs with skimmers that catch trash," said Janie Hagberg, the stormwater engineer who has been working on the Clam Bayou project since 2003. "The goal is to catch 90% of the trash before it enters the bayou."
The retrofit also will capture about 80% of suspended solids and about 60% of the nitrogen currently entering Clam Bayou, she adds. "It doesn't quite meet the 80% goal (for nutrients) but given the available land and the size of the basin area, it's the best we can do."
Like the earlier phases, water will be captured from current drainage systems that include lined canals designed to move water into the bayou as quickly as possible. Moving water more slowly, from a series of deep sumps and shallow ponds, then over weirs and through meandering streams allows sediments to settle and native plants to absorb excess nutrients.
While some residents question levels of polycyclic aromatic hydrocarbons (PAHs) found in Clam Bayou sediments, removing them would be prohibitively expensive and probably have more environmental impact than leaving them in place, Henningsen said. "They'll disperse over time, as we are able to treat stormwater before it enters the bayou."
New research from the U.S. Geological Survey indicates that coal tar-based pavement sealant is the largest source of PAHs in urban lakes, he adds. "Clam Bayou has a large watershed with a number of parking lots that appear to be resealed on a regular basis," he said.
The recreational elements in the final phase will include opportunities for walkers and cyclists as well as kayakers and fishers. An extension of the Pinellas Trail will wind through the restored wetlands, including a "string of pearls" recreated in a mangrove forest that had been bisected by mosquito ditches.
"The goal is to create as much shoreline as possible because it's the most productive habitat," Henningsen said. Capturing stormwater for treatment also helps create low-salinity habitats that are necessary for the juvenile stage of nearly all commercially important fish, including snook and tarpon. Once construction on the lagoons is complete, sediments will be removed from a narrow channel to facilitate tidal flows into the bayou.
Construction at Clam Bayou will continue through this summer with a grand opening scheduled for the fall, Henningsen said. "It's the culmination of many years of work and a shining example of how urban estuaries can be restored."
The Leisey Shell Pits near Ruskin — most well-known as a treasure trove of Ice Age fossils — will be restored as the final phase of construction at the Cockroach Bay Aquatic Preserve.
Once mined for shell used to build roads across the region and then slated for development, the land was purchased by the Hillsborough County's Environmental Lands Acquisition and Protection Program in 1991. But like Clam Bayou, restoration of Cockroach Bay has been a "pay as you go project," Henningsen quips.
The last phase of Cockroach Bay restoration will be performed by the Tampa Port Authority as mitigation for two new projects at the Port of Tampa. "They're mitigating for about 12 acres and we're getting 75 acres restored," he said.
Construction began in May and is expected to take about 10 months to complete.
Cockroach Bay is the centerpiece of a 20-mile corridor of nature and aquatic preserves bordering the eastern edge of Tampa Bay. The lands were largely purchased with ELAPP funding and restored through the water management district's SWIM program.