GAINESVILLE — The U.S. Army Corps of Engineers today has a full view of most of Lake Lanier’s often-murky depths, thanks to federal stimulus money in 2010 and some nifty technology.
A firm hired by the corps traveled the lake by boat using high-speed sonar, which provided elevation numbers throughout the reservoir, including in and around the many recreation areas filling the shoreline.
Crews also used light detection and ranging, which according to the National Oceanic and Atmospheric Administration, is a “remote sensing method used to examine the surface of the earth.”
“The only places they couldn’t get to are like way back in shallow coves,” said Russell Lundstrum, corps park ranger at Buford Dam.
The maps have amazed Lundstrum, who is working to refine them by updating geography and other key details.
They show the lake’s depths “in significant detail, like no other maps before this project,” he said during a visit at the project’s headquarters at Buford Dam in Gwinnett County.
The maps particularly prove useful in terms of water safety, allowing Lundstrum to pick out low-water hazards.
“We’re able to calculate the depth at what was previously hilltops,” Lundstrum said, referring to the manmade lake’s formation by flooding former valleys, including the homes and churches in them. “We have a better idea of where they are.”
Also, the maps have come in handy in recovery efforts, where emergency responders are looking for drowning victims.
“They have a better idea of what they’re getting into for a search area,” Lundstrum said.
He has shared maps with other agencies, such as the Georgia Department of Natural Resources, “but on short notice, I’m able to reproduce whatever they need pretty quickly.
“Whatever search area they have, I can print [a map] out quickly. I even send them digital copies of the data. But, typically, in emergency situations, they like to have paper maps where they can point at and draw on.”
“Our guys use it,” said Hall County Fire Services Chief David Kimbrell. “When they’re not on a call but out on the lake, they’ve actually driven [it] using a depth finder and the map, and have plotted the deepest waters.”
Kimbrell’s department operates a marine rescue unit.
“So even when the lake is well down and at night, they can use the [tools], even when it’s dark, and still make sure they’re in the deepest waters,” the chief added. “So it’s a big benefit to us.”
Upon closer review, the maps also point to the area’s past, before the lake and Buford Dam’s construction in the 1950s. The outline of landmarks, which went underwater when the lake was filled, show up clearly.
For example, the oval shape that sits off Laurel Park in north Hall once belonged to Gainesville Speedway, and there’s a roadbed where U.S. 129 brought traffic to the track. When the lake was built, U.S. 129, also known as Cleveland Highway, was rerouted west to the path it follows today.
Area residents got a glimpse of that history during the lake’s historic 2007-09 drought, which exposed part of the racetrack’s concrete grandstands.
Lundstrum pointed at a map showing what appeared to be bumps on the lake’s bottom, where a marina’s boat slips are located.
“It took me a while to figure that out,” he said. “Are those gravestones or houses? It turned out to be anchors — some of them are as big as cars, with big cables holding down these giant docks.”
The original Chattahoochee River channel also can be traced on the map.
Chestatee River also flows from the northwest into Lake Lanier, converging at a point south of Browns Bridge.
Some other landmarks, such as cemeteries and house foundations, that would have fallen under water as the corps filled the lake to full pool — now at 1,071 feet above sea level — aren’t as easily recognizable.
“I haven’t been able to see anything definite, because they’re fairly small,” Lundstrum said.
Of course, there have been other maps of the lake, just not as detailed.
“Every decade or so, there’ll be [depth] surveys at certain points in the lake,” the ranger said. “They would do cross-sections of the lake. But to get an overall picture, they haven’t been able to do an entire survey of the lake until [the stimulus project].”
The maps show an array of colors, with blue denoting water and its shades varying according to depths. Faint blues, for example, are seen in the shallow coves.
More than just a pretty picture, the map relates to storage and silt buildup, particularly around the shoreline.
The map, however, doesn’t provide any stark revelations about buildup “because this is a whole new baseline study,” Lundstrum said. “In 10 more years, we’ll do another [study] and have a more accurate idea.”
Siltation “is a natural process, but the whole point of analyzing [data] is to know how fast it’s happening, where and dredge it out,” he added.
The corps has had to dredge before in the lake, such as in Longwood Cove in 2008.
The $2.3 million project involved 125,000 cubic yards of silt removal, building a retaining wall and extending the greenway that runs into the park from downtown Gainesville.