LAKEWOOD RANCH -- The scouring action of the Braden River is causing erosion damage as it runs through trails, over banks and into nearby retention ponds, which send waterfalls pouring back into the river.
It last happened during Tropical Storm Andrea, but these overflows can occur with any heavy rain or summer storm so Community Development District 4, serving Greenbrook, is taking action to prevent the walking trail behind Adventure Park from collapsing.
"The banks were undercut, meaning that there was an underhang. The banks represent an unstable area, meaning that if someone actually walked on them, they would find themselves under the bank," said board Superintendent Joe Sidiski. "We may have lost an opportunity to do this in a dry
season, but I am concerned with what might happen in a more intense storm than we had. We had significant damage."
As Tropical Storm Andrea blew through Manatee County June 6, Sidiski said he observed water within inches of the top of the riverbank.
Superintendent Keith Davey said he saw a waterfall coming from the other pond. "We've got more than just the river to worry about here," Davey said.
The expanded erosion prompted the board to consult an engineer about possible solutions.
"Is there more that we ought to do here?" asked board Chairman Michael Griffin.
Sidiski suggested using stacked bags of concrete to block the water. Sidiski also suggested tiered "geo tubes."
"Usually the method is to pump the soil like a dredge," he said. "You tier this and you cover it with sod. Where we've done this at the Braden River Park, the bank just to the west under the spillway was undermined. It held very well. It's underwater, it's covered with soil and turf and there's a layer of it under the water."
Even though some water is exchanged between the ponds and the Braden River -- the source of Bradenton's drinking supply -- there is no contamination threat, said Claude Tankersley, city director of public works and utilities. "This is a rare event. Our reservoir holds a billion gallons. It's like a drop of water into a swimming pool, especially since we treat water to a high degree before it reaches our customers," he told supervisors.
Dee Graham, Herald reporter, can be reached at 941-745-7024, or tweet @ DeeGrahamBH.