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Just Another Case of a Sinkhole Wiping Out a Lake

July 19, 2006

Florida's Scott Lake recently has been at the mercy of a giant sinkhole that may be 300 ft. deep. When the sinkhole collapsed last month, it took only 10 days to swallow up the lake's water. Now engineers are trying to figure out how to plug and refill the lake.

Central Florida's Scott Lake, most likely formed by sinkholes thousands of years ago, recently has been at the mercy of a giant sinkhole that may be 300 ft. deep.

Four sinkholes and several inactive ones beneath the 285-acre lake, and another one in a nearby ridge, caused the lake to drain completely earlier this month. Water first began to drain into two sinkholes after they opened in mid June, flooding nearby homes and forcing wildlife such as snapping turtles and alligators to fight for their lives.

Two men walk across the dry lake bed of Scott Lake, photo by Rick Runion via The Ledger.jpgThe largest of the new sinkholes, possibly 300 ft. deep, collapsed only weeks ago. It grew into a gaping crevice at least 200 ft. in diameter and 15-20 ft. deep on a Wednesday, having expanded dramatically overnight, and channeled water into the Floridian aquifier, collapsing a dock, a concrete walkway and a chain-link fence. By noon on Wednesday, only isolated pools of water, no more than a foot or two deep, remained.

Engineers have confirmed four sinkholes in the lake and another one on a nearby private property are to blame for virtually emptying the lake in 10 days. The deepest one is thought to have sucked more than 90 percent of the water from the lake as it drained up to 1 billion gallons last month, according to Richard Powers, president and CEO engineering firm BCI Engineers & Scientists.

That sinkhole is oval in shape, about 150 to 160 feet long by 100 feet wide. It is estimated to be at least 150 feet deep but could go as far down as 300 feet.

Another oval sinkhole measures 375 feet-by-about 300 feet. The sinkhole has not collapsed, but is depressed about 5 feet to 10 feet like the two smaller ones to the west.

Sinkholes form when groundwater levels drop, leaving empty crevices and cavities in the limestone liquefier. They are largely seasonal, according to Ann Tihansky, a sinkhole expert with the U.S. Geological survey in St. Petersburg. During the dry months of March-May, the aquifier levels decrease. Then the first hard rains in June funnel the sand and clay into the underlying cavities. On dry land, a heavy rain can wash overlaying clay and sand into the aquifier, creating a hole at the surface. In the case of Scott Lake, the holes opened up beneath the lakebed.

Although the disappearing lake and growing sinkhole attracted a great number of curious visitors, such events are not really that rare in the state, Florida Geological Survey geologist Harley Means recently told The Tampa Tribune. While sinkholes are a common problem in Florida with its high water table, Powers says it is "extremely rare" to have one form beneath a lake that triggers total draining.

Yet even what typically passes as atypical — that is, that the sinkhole(s) opened up under a lake basin — is not uncommon in Florida: it is not the first time one of the state's lakes has had a sinkhole that swallowed up the water.

Lake Jackson near Tallahassee has drained five times since 1999, although never completely. The 4,000-acre lake acts like a bathtub about every 25 years, when sinkholes open and drain portions of the lake, according to a Department of Environmental Protection (EPA) Web page.

Also, consider Alachua Lake near Gainesville. Having once allowed steamers to haul fruit between Micanopy and the lake's location, it drained 8 ft. in 10 days in the 1800s — leaving thousands of rotting fish, according to a Florida parks Web site.

The recent waterless Scott Lake may fall somewhere between the extremes of the sinkhole-riddled lakes.

While plans for restoring Scott Lake are still in the works, BCI Engineers & Scientists has generated a graphic that gives a layman's view of what's at play in the 285-acre lake.jpg

Now, with Scott Lake in a holding pattern, engineers are getting closer to finding out what's going on with sinkholes that sucked between 750 million and 1 billion gallons of water from the 285-acre lake. BCI Engineers & Scientists in Lakeland, where Scott Lake is located, is formulating plans on what, if anything, can be done to stop the sinkholes from draining more of the lake. Carl Christmann, a senior geotechnical engineer for BCI, said a course of action couldn't be recommended until the sinkhole stops draining; he said it appeared water had stopped draining into one of the sinkholes.

Engineers and Dave Curry, spokesman for the lake residents, have talked about building a dam near the deepest sinkhole so they could examine and fix the problem.

BCI is trying to repair the damage and figure out how to install a permanent plug. The lake shoreline, parts of which have sunk into the sinkhole, must be restored. The firm must also determine how to refill the lake, either with sand or grout or both. Rain and runoff from the surrounding watershed eventually will fill the lake, Christmann said.

According to Ted Smith of BCI, the sinkholes appear to be plugged for the time being. Whether it's completely plugged, Christmann followed, "I doubt it. Whether it's going to stay that way, that's a wait-and-see." It's not unusual for these features to partially plug themselves, then the water accumulates and the water pressure causes the sinkhole to reactivate, he continued.

BCI has considered using three-dimensional seismic investigative methods to assess the area beneath the lakebed. This would help determine "the magnitude and complexity of what's down there," says Powers.

Public agencies such as the Southwest Florida Water Management District have said they do not plan to do anything with the sinkholes, as they are a natural phenomenon. Although Scott Lake is a private lake, its bottom is under the jurisdiction of Florida's Department of Environmental Protection.

The phenomenon has gained a steady stream of amazed visitors. Powers says that the sinkhole could yet disappear on its own. It remains too early to establish a timeframe for mitigation.

Sources

Engineers Map Scott Lake Woes

by Diane Lacey Allen

The Ledger, July 15, 2006

Engineers Move To Find Out Why a Lake Lost its Water

by Alisa Zevin

Engineering-News Record, July 3, 2006

Engineers plug sinkholes that drained Scott Lake

by Daphne Sashin, Mark Pino, Amy L. Edwards and Mark Andrews

The Orlando Sentinel, July 5, 2006

Talks Begin on Fixing Lake

by Diane Lacey Allen

The Ledger, June 29, 2006

Experts: Activity of Scott Lake Sinkholes Is Difficult to Predict

by Diane Lacey Allen

The Ledger, June 24, 2006

Sinkhole Swallows Scott Lake

by Mike Salinero

The Tampa Tribune, June 22, 2006