Water flow from Lake Lanier to drop 16% by November 15
A deal reached today by the governors of Georgia, Alabama and Florida will reduce the water flowing out of Lake Lanier by 16% starting as soon as November 15.
Officials say that this will certainly improve the length of remaining water supply, but they couldn’t say how much longer it would make it last. Let’s try to figure it out. Please realize that these are very rough numbers and they’re intended to just give us a crude estimate.
Today the lake had about a 150 million gallon inflow (mostly via the river) and about a 950 million gallon outflow through the dam for a net loss of around 800 million gallons (stats). These seem to be fairly typical figures. The lake dropped an average of 0.12 feet each day for the past four weeks. Based on that, we can say that an 800 million gallon loss results in a drop of about 0.12 feet.
If they reduce the outflow by 16%, that means it will only have a daily outflow of around 800 million gallons (instead of 950 million). Combined with the inflow of 150 million gallons, the total daily loss will only be 650 million gallons — a reduction of 19% in the total loss. If we then reduce the 0.12 feet by 19%, it become a daily loss of only 0.10 feet.
We’ve got about 20.5 feet to go until we hit the “dead pool”. Losing 0.10 feet per day gives us 205 days worth of water left, not counting whatever they can pump out of the dead pool. Not bad!
Any major mistakes in my math? I wouldn’t doubt it. :) Let me know in the comments.
November 2nd, 2007 at 10:58 am
One possible flaw is that your math assumes the level drops in line with the volume. This is true if Lanier has vertical sides like a barrel. However, a bowl with sloped sides is probably closer to the truth. If the sides are assumed to be sloped, the height will fall more for each subsequent reduction in volume.
I put together a quick excel model. Based on the initial conditions (20.5ft with 110 days left for 800M gal/day net outflow) the model estimates an angle closer to a plate (less than 1% slope); at 800M gallons per day the model shows 20.5 ft gone in 120 days; 650M gallons per day only extended the life of the volume to 145 days.
I can send you the spreadsheet if your interested.
-Zoli
November 2nd, 2007 at 11:39 am
I’d love to see the spreadsheet.
I covered what you’re talking about in a previous post, but didn’t try to figure that in here.
http://www.atlantawatershortage.com/20071017/understanding-lake-laniers-level/
I knew that it would be a factor, but had no clue how to calculate it in. Thanks for the info!
November 2nd, 2007 at 12:05 pm
No worries. Spreadsheet on it’s way; very rough model based on a cone, but probably closer than a barrel.
Sadly, my previous comment was an overestimate. The model shows 111 days left for 800M g/d and 136 days if net outflow was reduced to 650M g/d.
I just stumbled on your site. It’s alot easier to find up-to-date info here than via msm or official sites. Thanks for the work that you’re doing. -z-
November 2nd, 2007 at 1:13 pm
Aren’t you attributing the entire 0.12 foot per day loss of the lake to the release of water for downstream use by the Corps of Engineers?
Am I missing something? Does Atlanta pull their water for daily use from that billion gallon release as well? If not, then that 0.12 feet per day comes from both the release for downstream use, AND the normal usage of Atlanta and the surrounding region.
That’d make your math off - the 16% reduction of just the downstream release wouldn’t reduce the water loss from 0.12 to 0.10 feet per day.
Again though, I don’t know the actual situation there. Am I wrong?
November 2nd, 2007 at 1:26 pm
Your math also does not take into account evaporation, which will be unaffected by the reduction in outflow, but will be reduced both by reductions in surface area (as the water level falls) and by cooler temperatures. It appears that the evaporation rate is about 0.01 ft/day. http://www.grow.arizona.edu/Grow–GrowResources.php?ResourceId=208
November 2nd, 2007 at 1:36 pm
If I understand correctly, the Atlanta water supply is pulled from the river south of the dam — after it’s been released by the Corps. Part of the Corps calculation into how much water is released takes into account the amount that will be pulled from the river by the city of Atlanta.
While some other areas have intakes directly in Lanier, I don’t think the city of Atlanta does. Technically, those other intakes should be factored in but they’re a rather small percent of the daily water loss.
If all of that is correct, then yes — pretty much the entire 0.12 foot/day loss can be attributed to the releases by the Corps.
November 3rd, 2007 at 5:36 am
How is there a simultaneous concern of an abundance of water due to global warming and a water shortage in the South?
November 3rd, 2007 at 12:20 pm
Forget about lake lanier, and go out and buy at least 100 days of drinking water. Store it in your basement. The Red Cross estimates that each person needs at least 1 gallon a day just for consumption purposes. Also, you may wat to store tap water for washing. Don`t wait until there is nothing left, you thought people were mad at the gas pumps?? Wait until there is no water. I am a Stock Trader, and have been buying water stocks for my portfolio, how much would you pay for a glass??
November 3rd, 2007 at 9:32 pm
[...] going to dig a bit deeper into the numbers we posted a few days ago. I’ll give the starting numbers so that those of you mathematically inclined and try your [...]
November 4th, 2007 at 3:18 am
Stocktrader, maybe you should short sell stocks of atlanta real estate companies. Once the facuets run dry, nobody will be moving to atlanta. Existing property will be worthless without toilets and showers. Yes the lake will fill up again, but atlanta will not stop growing…this problem is here forever.
November 5th, 2007 at 3:02 pm
[...] how many days worth of water were left in Lake Lanier, based on the new information that the flow through Buford Dam would be cut by 16% in a few [...]
November 6th, 2007 at 8:49 pm
[...] imagine that the decision to cut the flow from Buford Dam had a lot to do with [...]
November 9th, 2007 at 2:39 pm
[...] and the fishing industry, Florida Gov. Charlie Crist is now in opposition of the plan to cut the water flow from Lake Lanier. He cites irreversible damage to Florida’s environment and [...]
November 13th, 2007 at 2:35 pm
Sadly, I think the above calculations fail to account for lake Lanier’s extremely jagged coast line. The lake when full is like an extremely broken mirror, with channels that run from a 1/4 to 1 mile up away from the main body of the lake. And since people normally run boats up these tributaries, I’m guessing that the average depth to be 8 feet. Thus with these now gone, clearly up to 50 % of what has been taken from the lake has come from these channels. And If we assume that this represents at least 15 % of the lakes total volume, then with all future withdrawls coming from the main body, the drop rate should increase by 15 %. Or if the 136 days above is fair for a bowl, then that would decrease to 115 days, now that the channels are all but gone and drained into the main body of the lake.
November 13th, 2007 at 11:34 pm
Does anybody know how many gallons per day the corp releases and
how much the city of Atlanta uses each day. I believe that the numbers wouild show that all our rationing etc probably only saves what they
release in 30 minutes.
Also , everyone in Cobb County know that they Drain Lake Altoona to
about 1/2 or more every winter. They say it is flood control . They have
done it for 40 years that I know of. Did they do it this year. If not,
can we stop them from doing it ?
November 14th, 2007 at 11:20 pm
One big issue missed is the apparent desperation of the corps to release as much water as possible prior to the 15th. Since last Friday the corps has been releasing approximately 2 billion gallons per day. I first noticed this by seeing the river rise and staying there for longer than I have seen in several years (I lived on the river until a few months ago). I’ve called the news channel, the Corps and the Governor’s office, but nobody is answering why so much water is being released. What’s up? Do they want us to go in to a draught?
November 14th, 2007 at 11:56 pm
Mitch - There is some discussion about that in our forums. This link should help:
http://www.atlantawatershortage.com/forums/index.php/topic,11.0.html
November 15th, 2007 at 2:50 pm
[...] 16% reduction that may or may not happen starting today would be a reduction in that 5,000 cfs mandate, lowering it 4200 cfs. This would mean that the [...]
November 15th, 2007 at 4:05 pm
Hey Mitch, the reason why the Chat river out of lake lanier is running stong right now, is because the Corp of Idiots has drained lake Allatoona to almost the limit. Before, that lake supplied 40 % of the flow, but now can only sustain 20 %. Thus Lake Lanier has to make up the difference.
November 16th, 2007 at 12:16 am
[...] A decision is due tomorrow on the now-famous 16% reduction that we’ve been talking about for a few weeks. The bottom line is whether or not the federally protected mussels can live with less water. If so, that’s exactly what they’ll get. [...]
March 20th, 2008 at 3:24 pm
That property is gorgeous. It’s hard to find nice lake front property for a reasonable price anymore.