Twelve days after winds from Tropical Storm Elsa swept through Alachua County, roads have opened up, river levels are dropping and crews have patched depressions and sinkholes that opened up in the storm’s wake.
By Friday, crews were working at Newberry Corners off US Highway 27, where a roughly 75-foot long series of sinkholes started opening up around July 7.
At Tioga Town Center, where depressions and sinkholes have opened up in the retention pond in front of the marquee after storm events in the past, another series of gaps measuring about 15 long by 15 feet wide appeared near the sidewalk, east of the Tioga Town Center letters.
The areas in both locations were promptly enclosed with temporary fencing and at Tioga Town Center “No Trespassing” signs were posted.
James Olson, director of geology at Geohazards in Gainesville said Jonesville and Newberry have plenty of near-surface limestone and retention ponds, so depressions and sinkholes are common after heavy rain events.
According to Olson, near-surface limestone means there is limestone within 20 feet of the surface.
And in western Alachua County in Jonesville and Newberry, Olson said, “There’s not much clay between the sand and limestone.”
Olson said clay helps insulate limestone from the direct impact of water and heavy rain events that cause wet sand to rush to fill in the gaps in the limestone, which is when the ground caves in.
“We will see them more often in retention ponds because we put more water in there,” Olson said.
Olson has inspected more than 1,000 sinkholes from Key West to Georgia, Tennessee and the Caribbean. Officials bring him in to help diagnose the problem and then help develop a remediation strategy.
He said because the latest sinkholes happened in retention ponds and at least 50 to 100 feet away from structures, filling them in is the right first step to stabilize them. If the HOA or business wants to take remediation further, they would hire a company like his to do geophysical testing to measure the subsurface cavities.
If sinkholes are near where people will be driving or walking or near buildings, remediation usually involves compaction grouting,” Olson said. “Compaction grouting is pumping concrete into the ground at a high pressure.”
Olson said that kind of remediation can get expensive, which is why a lot of places start with filling in the holes with different size aggregate starting with larger rocks and layering them with smaller aggregate toward the surface.
Olson referred to the sinkhole that opened up last year in Gainesville as an example of a one that may not be able to be remedied. The hole claimed multiple properties and tripled in size from 40 feet across by 30 feet deep in October 2020 to more than 100 feet across by 120 feet deep in April 2021.
“There’s always a point to where the ground will stabilize,” he said. “But it won’t while there are vertical sides.”