It’s illegal to touch a West Indian manatee everywhere in the U.S. except Crystal River, Fla. Every year, at least 250,000 boaters, divers, snorkelers, and swimmers flock to a wildlife refuge outside the city for an up close and personal experience with the gentle mammal.
Three Sisters Springs is one of Florida’s last remaining urban springs and, at a consistent 72° F , important habitat for the endangered species. Despite their size, manatees have relatively little body fat and a low metabolic rate. If exposed to water temperatures below 68° F for an extended period, they can die.
Over the last several years, more manatees, including mother-calf pairs, have wintered in the springs. In February 2016 more than 500 sought shelter from falling water temperatures, prompting the U.S. Fish and Wildlife Service to temporarily suspend public access.
While important to the city’s economy, the annual influx of people and animals also brings challenges: shoreline erosion and siltation in Florida’s second-largest spring system.
“I’ve heard visitors speaking French, German, and even Russian,” says Stantec Senior Ecologist Mike Jones. “From a local, state, federal, and even global perspective, Three Sisters Springs is worth safeguarding.”
Many nibbles = big losses
The 57-acre site that’s now Three Sisters Springs was cleared years ago to prepare for a 300-unit waterfront development that investors abandoned after helping rescue a young manatee injured in a boat incident. Only a narrow band of native vegetation around the springs remained.
When the investors put the parcel up for sale, the Friends of Crystal River National Wildlife Refuge Complex began working with the Florida Communities Trust to buy it. Located about an hour drive north of Tampa, the parcel is part of the state’s second largest springs group, with 70 springs scattered over 600 acres.
In 2010, after extensive state, federal, and local collaboration, the property was purchased for $10.5 million. The City of Crystal River and Southwest Florida Water Management District (SWFWMD) share ownership; the U.S. Fish and Wildlife Service (USFWS) manages the property as part of the Crystal River National Wildlife Refuge.
Shortly thereafter, conservation managers observed that the springs' banks showed losses that threatened to eliminate natural vegetation along the shore. Trees had fallen into the water. Manatees nibbling on the exposed roots scraped against the shore, further eroding the land. Sediment was accumulating over the spring vents.
In addition to loss of riparian habitat and degraded water quality, visitor safety was becoming a major concern along 1,200 feet of shoreline.
Successful cat-herding
In January 2015, the Southwest Florida Water Management District retained engineering firm Stantec to oversee stabilization design and coordinate stakeholder involvement.
In addition to finding a solution that enhanced rather than detracted from the springs, the agency’s major concern was getting the project’s numerous stakeholders on the same page. In addition to SWFWMD, USFWS, Friends of Crystal River National Wildlife Refuge Complex, Florida Communities Trust, and the City of Crystal River, they included the Florida Department of Environmental Protection and Florida Fish and Wildlife Conservation Commission.
The design was required to sustainably support the shoreline, look natural, and be built without further damaging the shore, trees, and vegetation.
“State and federal wildlife agencies were involved with the design team from the beginning, and it really helped having everyone actively looking at solutions,” says SWFWMD Project Manager Sky Notestein. “It took years of planning and lots of participant input, but the final design solution was successful thanks to this coordination.”
Sometimes nature needs a hand
The first step was to fill bank voids with soil. Because the challenge was similar to stream restoration, the first design used geotextile fabric to anchor a retaining wall made of boulders and gravel. However, given the springs’ constantly flowing water, the structure would have been almost impossible to secure and could have further degraded water quality.
The restoration plan preserves onsite trees, including oaks, bays, maples, palms, and cedars. To provide structural support while preventing further loss of earth through erosion, the soil was encapsulated.
Manufactured by Nilex Inc., which has offices in Denver and Salt Lake City, Envirolok bags are made of non-woven fabric that tree roots easily grow through to reach and penetrate soil. The fabric eventually decays, leaving a continuous soil medium that requires minimal maintenance.
“Over time, tree roots will lock together and further stabilize the area, encouraging nature to heal itself,” says Jones.
The process is being helped along by using soil-filled bags to plant grasses and bushes found in similar riparian habitats. In addition to keeping topsoil in place through storms and tide fluctuations, the vegetation discourages people from walking along the bank.
A bed of pea gravel was installed at the new slope’s base to create a firm foundation for limestone boulders and act as mortar by filling voids between the boulders and soil bags. The dual-purpose application produces a more resilient structure.
Limestone boulders were chosen as the stabilizing element because they’re native to Florida, had minimized erosion elsewhere along the shoreline, and form a spring bank that looks like naturally exposed rock strata along the shore.
“People didn’t want to look at a seawall along the bank,” says Notestein. “Using these materials allowed for a constructable project that improves over time.”
Design team is hands-on, literally
The design team spent hundreds of hours in the water measuring the undercut shoreline to determine how many bags and material would be needed. As a result, SWFWMD received a much more precise quantity estimate, allowing for accurate budgeting and bidding and averting cost overruns caused by too much or too little material.
The contractor, Diversified Professional Services Corp., began construction in April 2016.
Floating turbidity barriers placed around the site isolated the work area and kept disturbed, sediment-laden water from entering the rest of the springs and spring run.
Crews used a crane to lower three sectional barges and a 60,000-pound excavator into the springs without damaging a single tree. They’re hand-placing more than 5,000 60-pound bags under the eroded banks. Some undercut areas were as far back as 10 feet under the top of the bank, making for an arduous, labor-intensive process. The excavator placed the bedding stone and then set individual limestone boulders in place.
When construction is completed in November 2016, the renewed shoreline will be ready just in time for manatee season.
