Why are Lake Levels not Rising?

February 20th, 2017 Posted by Full Lake 0 comments on “Why are Lake Levels not Rising?”

We have had several members asking questions about lake levels. We thought a group communication might be helpful at this point.

It’s been raining, right? So why isn’t Lanier’s water level going up?
As this is being written, Lanier is at essentially the same level as it was in December and January, and about a foot below the same date in November. But it’s rained about five inches (about average) around Lanier since the beginning of the year and the average discharges from Buford Dam are the lowest they’ve been since late 2014. In fact, this month the average discharge has been 733 cfs and in January was 932 cfs. Compared to the same period last year, the discharges for the first of 2016 was over 6,000 cfs. The current discharges are barely enough to meet the water demands of Metro Atlanta below Buford Dam. So what’s going on?

In fact, Lanier just entered Zone 4, which is alarming for mid-February (the middle of the rainy season). The Corps’ forecast is for lake levels to decline from here. Historically, lake levels start rising in December and continue into April – but this year they haven’t.

In the entire ACF system, composite storage is in Zone 3, and if it stays at its current level total ACF conservation storage will be in Zone 4 by mid-April, which is very concerning. You have to go back to 2008 and 2009 to see those levels at this time of year – and in 2008 we were just starting to come back from the worst drought in Lanier’s history, during which lake levels got as low as 1050.8 the day after Christmas of 2007. So where is the rain going?

Gainesville rainfall has been about 32″ over the last 12 months, which is about 21″ under normal precipitation levels. Soil moisture is currently only about 24%, which means that most of the rain we’re getting now is soaking into the ground like a sponge – good for plants, but not raising the lake. The two main rivers that feed the lake – the Chattahoochee and the Chestatee – are flowing at about 274 and 122 cfs, respectively, for a very low total of 396 cfs even after the recent rains. That is extremely low and well below the volume of water being discharged through the dam to maintain necessary downstream water quality flows. Except for a few days, the Chestatee hasn’t been above 600 cfs since last February, and the Chattahoochee has exceeded 1000 cfs only about 30 times, only a handful of which have occurred since the beginning of August.

So, the reason the lake isn’t rising is pretty simple: not enough water is flowing in to exceed what’s being let out at the dam. While a lot of people are asking whether the Corps is releasing unusual or excessive amounts of water, we don’t see any evidence of it. Recently the minimum flow at Peachtree Creek was reduced from 750 cfs to 650 cfs which benefitted the lake to some extent. It’s just not raining enough to overcome a long period of drought.

So what’s likely to happen between now and the start of boating season?
Unfortunately, the most recent drought forecast indicated Lanier is still in a severe drought and the ACF has a likelihood of below-average rainfall for the rest of the winter. So, the picture is pretty bleak right now – unless we start getting a lot more rain pretty soon, we might be in for a very low lake this summer.

Even when Lanier can’t refill because of too little rain, the system continues to rely on it for minimum downstream water quality flows. In March, the Corps raises Apalachicola River flows to support Gulf Sturgeon spawning, and that puts additional pressure on Lanier. If more rain doesn’t come soon to Lanier, water levels may start dropping rather than rising as they usually do during the winter and spring. And that is not something anybody wants to happen.

But keep in mind that Lanier has always depended on large rain events for refilling. A couple of examples: from January 5-19, 2009, the lake rose 3 feet, and during the last 10 days of September, 2009, it rose more than 3.5 feet. So, it is not unprecedented for the lake to stage a quick and dramatic recovery. We just don’t know when the next large rain event might happen.

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