1111intakesaudGainesville Public Utilities Director Kelly Randall explains why the city has water intakes operating at several different lake levels.
As the drought continues to draw down Lake Lanier and other reservoirs in Georgia, some municipal water intakes have been left high and dry.
That's because they have horizontal pipes that can only draw water from one level. If the lake drops below that point, the pipe becomes unusable. And just like most of the lake's boat ramps, an extension would have to be built in order to reach the water's surface again.
For example, one of the city of Cumming's two intakes cannot draw water if Lake Lanier falls below 1,053 feet above sea level, which means it could be out of service within a couple of weeks.
Jon Heard, Cumming Utilities director, said the first intake was built in the 1970s, when "there was no historical data that indicated that the lake would go below the 1,053 elevation."
A drought in the early 1980s convinced the city to build a second intake at 1,033 feet. But for Gainesville Public Utilities, adjusting intakes to accommodate the shrinking lake has not been an issue.
"Our intakes already go all the way down to the bottom of the lake," said Horace Gee, environmental services administrator for Gainesville. "The two intakes at the Riverside (water treatment) plant are like vertical pipes with holes cut in at three levels."
With Lanier at less than 1,055 feet, the topmost portals of both Riverside intakes are now sticking out above the water. But the middle and bottom portals are still in use.
And the lowest levels at both Riverside and the new Lakeside plant will continue to be in service even if Lanier drops below the conservation pool of 1,035 feet.
The conservation pool is the upper 60 percent of the lake that is considered easily available for drinking water. Riverside's original intake goes all the way down to the Chattahoochee River channel, at 1,024 feet.
"The oldest one was literally built before the lake was there, around 1953," said Kelly Randall, director of Gainesville Public Utilities.
Initially, the first Riverside intake could pump just 4 million gallons per day. As Gainesville's population grew, more pumping capacity was added. But Randall said it reached a point where it could not handle more pumps, so in 1999 a new, similarly designed intake structure was built as part of a $20 million renovation of the Riverside plant.
Together, the Georgia Environmental Protection Division allows the two intakes to withdraw up to 25 million gallons per day,
In 2002, Gainesville built a second water treatment plant, Lakeside, off Jim Crow Road. This time, the city decided to use a different type of intake structure.
"There's a lot of things that go into a design, whether it's vertical or horizontal," said Randall. "One of the controlling factors is where it's located. When we sited the Lakeside plant, we spent a fair amount of time looking for the deepest water we could find for where we were going to put the intake structure. Then we determined where we were going to put the water plant."
In contrast to the Riverside intakes, which resemble giant smokestacks rooted at the bottom of the lake and connected to land by a pier, Lakeside's pump station is entirely on land. But beneath it lies a hidden structure drilled down into rock. "It's a big hole in the ground, like a manhole, and at the bottom there's a pipe that goes out into the lake," said Randall.
Actually there are two pipes. One can withdraw water down to the level of about 1,046 feet. The other can be used as low as 1,023 feet. "We designed it just in case there was ever a situation where we needed to draw water below the conservation pool," said Randall.
They also designed it to accommodate growth. Though Lakeside currently has an EPD permit to withdraw up to 10 million gallons per day, from a technological standpoint it could handle up to 100 million.
"Now, I don't think I'll ever get a permit (from EPD) for that much," said Randall. "But because it is so expensive and difficult to put another ‘straw' into the lake, we just wanted to build it once and build it big enough."
He said that would avoid the problem they had at Riverside, where a second intake had to be built.
The total cost of the Lakeside project was $52 million, and about $10 million of that was for the intake. The mouth of the Lakeside intake is in the Chattahoochee Bay, about a mile and a half away from the plant.
Randall said the design of the Lakeside intake is similar to Gwinnett County's water withdrawal structure in Lanier. Both have horizontal pipes, but lines run close to the bottom of the lake, unlike some of the older horizontal intakes that become stranded above the water during a drought.
But if the lowest pipe or portal can always be used no matter how low the lake goes, why does each intake have more than one?
Randall said this design allows the city to draw water from different levels of the lake at the same time and mix the streams together.
"The water stratifies and has different water qualities at different times of the year, and you want to pull from the port that has the best water quality," said Randall.
For example, he said, they try to select the water level that has the least amount of algae, because algae can give drinking water an off taste even after it's been treated.
Gee said the design of Gainesville's intakes gives utility officials peace of mind, knowing they won't have to build an extension no matter how low the lake drops. "In terms of intakes, we're in better shape than anyone," he said. "We should be able to pump at almost full volume regardless of the lake level."