Building it back up

A national wildlife refuge, Three Sisters Springs is part of the largest winter sanctuary for West Indian manatees on Florida’s Gulf Coast. More than 1,000 feet of shoreline was cleared in 2005 to make way for development that never occurred. With nothing to hold onto, trees slid into the water. This is what the project site looked like when construction began in April 2016.

Manatees loved nibbling on exposed tree roots, but their bodies caused further erosion by scraping away at the banks. Coupled with human activity and daily tidal water level changes, riparian habitat was lost and sediment accumulated over the spring vents.

Floating silt barriers prevent sediment-laden water from migrating downstream during construction. The City of Crystal River and Southwest Florida Water Management District wanted a solution that looks natural. Instead of a traditional retaining wall, boulders made of Florida limestone were placed atop a bed of pea gravel. The gravel was also used to fill voids between the boulders.

Soil placed in biodegradable bags played two roles in the shoreline’s restoration. Stabilization began by placing the bags under bank voids and against exposed tree roots. The bags also are being used to re-establish vegetation along the reconstructed shoreline.

The contractor, Diversified Professional Services Corp. of Dade City, Fla., lowered a 60,000-pound excavator into the springs without damaging a single tree. The machine was necessary to lift and place the limestone boulders, which weighed one-half to four tons.

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