Mayos Bar Flow Analysis

Mayos Bar Flow Analysis 2018-04-11T10:10:11+00:00

ACT Compact Extended

The States of Alabama and Georgia have agreed to extend the deadline for the Alabama-Coosa-Tallapoosa (ACT) River Basin Compact to June 29, 2001. The ACT Committee will meet June 22 in Atlanta to discuss a water allocation agreement to which both states tentatively agreed last December. Georgia agreed on the provision that a companion agreement on the Apalachicola-Chattahoochee-Flint (ACF) Basin would also be forthcoming. A copy of the ACF proposal by Florida, dated May 25th, 2001, is on the Internet at

Proposed Agreement Draws Fire

The tentative ACT agreement, dated December 13, 2000, has drawn fire from the Rome area in northwest Georgia and Weiss Lake residents in northeast Alabama. Chief among many concerns are a provision that caps withdrawals from any basin at 25% of the average annual daily flow and the complex formula that sets minimum flows at Mayo’s Bar Lock and Dam on the Coosa River near Rome in times of drought.

25% Average Annual Daily Flow Cap on Withdrawal – Purpose?

The limitation of 25% of the average annual daily flow in a basin is an attempt to cap the amount of water Georgia can withdraw at any time. At Mayo’s Bar just west of Rome, where the measurement is taken of how much water comes across the state line into Alabama, the historical average annual daily flow is approximately 6600 cubic feet per second (cfs). Twenty-five per cent of that figure is 1650 cfs. Using the conversion of 1.54 cfs is equal to a million gallons a day (mgd) flowing past a defined point, Georgia could theoretically withdraw up to 1.07 billion gallons a day. That’s billion – with a “b.” Negotiators counter that horrendous prospect by noting that it would be physically impossible for Georgia to construct enough reservoirs or build enough systems to withdraw that much water. If so, then why set the limit so high? Perhaps it’s because Georgia has insisted the limitations apply to basins within Alabama also, forcing Alabama to keep the cap as high as possible.

Can Georgia Use a Billion Gallons a Day?

Could Georgia realistically withdraw or use that much water? Based on current assessments, probably not, but predictions are just that: predictions. Georgia negotiators say their demands would be approximately 340 mgd in 2030 versus approximately 180 mgd today. Again, why set the limit so high? Expectation breeds expectation. If the room to expand is there, the inclination will be to fill the capacity. Perhaps what sticks in the craw of the people in Cherokee County, Alabama is just the idea that the agreement would allow Georgia to withdraw over a billion gallons, which would severely affect flows into Weiss Lake during droughts. Another sticking point is that the billion gallons potential has not been modeled to show effects on the Coosa Basin.

Mayo’s Bar Flow Analysis

The prospect of such huge withdrawal rates boggles the mind, but perhaps more at hand would be the minimum flow rates stipulated at Mayo’s Bar during droughts. Under the agreement, water releases from Allatoona and Carters Lake Reservoirs are governed by seasonal guide curves based on water level elevation in the reservoirs, which will then dictate how much flow the US Army Corps of Engineers must provide at Mayo’s Bar.

The agreement assigns both Allatoona and Carters three guide curves of elevation levels of water to help the Corps manage releases. The curves were established based on historical data, predictive modeling, and an evaluation of demands on the system. The Top of Conservation line represents a full pool seasonally adjusted. An Intermediate Guide Curve, also seasonally adjusted, comes into play as water levels decrease for whatever reason. (At Allatoona, the Intermediate Guide Curve is from 5 to 12 feet below full pool. At Carters, it’s 7 to 9 feet below full pool.) The Lower Guide Curve (from 14 to 20 feet below full pool at Allatoona and 12 to14 feet below full pool at Carters) is that elevation below which the Corps would reduce discharges to what is known as “at-site” requirements or approximately 240 cfs. (The ACT agreement, including the guide curves, can be found at and then clicking on the Water Resources link to the ACT agreement page.)

The guidelines are complex, but basically a weekly average flow of 1800 cfs is guaranteed until the water levels at both reservoirs fall below the intermediate guide curve during a drought, at which time the guaranteed minimum is 1200 cfs. If we have the worst drought imaginable and reservoir levels are down below any in recorded history, i.e., below the Lower Guide Curve, then there is no guarantee except required releases of 240 cfs at both Allatoona and Carters. (Guidance governing flow rates at Mayo’s Bar is more complicated than just described, but this is the gist of it.)

One of the problems with the current state of negotiations is that no analysis of the drought over the last three years has been made available. If the proposed agreement had been in effect during 2000, how would flows into Alabama have been affected?

Such an analysis requires a look at data for the past three years for elevation levels at Allatoona and Carters as well as for daily flow rates at Mayo’s Bar. The elevation levels at both reservoirs then would have to be compared to the proposed guide curves for each. For the year 2000, that comparison reveals that elevations at Allatoona would have been above the intermediate guide curve from January through July, but below from August through November. At no time did the elevation level aproach the lower guide curve. According to the complex guidance in Section 2.2 of the agreement, that means that the minimum required flow at Mayo’s Bar would have been 1800 cfs through July and 1200 cfs thereafter through November. At Carters Lake the elevations were above the intermediate guide curve until the middle of August and below the rest of the year, reinforcing the minimum guidance of 1200 cfs at Mayo’s Bar. The Carters elevation did not approach the lower guide curve.

So what were the flow rates at Mayo’s Bar from August through November in 2000? US Geological Survey (USGS) data shows a weekly average daily flow rate over that time period of 2545 cfs, with values ranging from a low of 1245 cfs average during the week (Monday – Sunday) of October 23-29 to a high of 5086 cfs average during the week of November 6-12. (USGS cautions those data are preliminary and subject to validation.) During the three-week period from October 16th to November 5th when the most severe conditions existed, the average weekly flow rates were 1436, 1245, and 1449. There were 11 days, mostly in October, when the flow rate actually dipped below the 1200 cfs line, six of which were below 1000 with a low of 933 cfs on October 16th.

Based on these data, the minimum flows would have been met without any need to release additional water from Allatoona or Carters. Of course, this scenario does not include any of the future demands anticipated for the system. Fast forward now to 2030 and Georgia’s prediction of another 160 mgd over today’s demand on the system is realized, an equivalent decrease of approximately 246 cfs at Mayo’s Bar. With the same rainfall pattern as experienced in 2000, such a reduction would pull the weekly average for the week October 16-22 below the 1200 cfs minimum. Assuming the flow data are available on a timely basis, the Corps would then release water from either Allatoona or Carters to meet the minimum, which would have been required for the following week. The assumption here is key. When would the flow data be available? How long would it take the Corps to act? A delay of more than a day or two before acting would mean the guaranteed minimums during the week of October 23-29 would most likely not be met.

Reporting System Critical to Agreement

Significant to all of this is the kind of management system to monitor the flows and decide when and how much water to release from Allatoona and Carters to maintain the minimums at Mayo’s Bar. Based on the current USGS practice of taking an extended period of time to verify flow rate data, it could be a long while, perhaps weeks, to determine that flows at Mayo’s Bar are not meeting the minimum required and to adjust releases from Allatoona and Carters. By that time, management data are irrelevant to the current situation.

Reporting System Must be Accurate and Responsive to be Effective

The flow criteria in the proposed agreement put a premium on the need for an accurate and responsive reporting system, but nowhere does the agreement stipulate the parameters on which such a system must operate, e.g., accurate flow data must be available for analysis within 24-48 hours to facilitate timely management decisions. If the basic agreement does not make these kind of stipulations, then the proposed drought plan should. Otherwise, the agreement is ineffective.

States Owe Stakeholders Explanation

Weiss Lake depends on flow rates to sustain its ecological health. The people in that area deserve to know how this agreement affects them. The analysis presented above is perhaps oversimplified, but it serves to point out the need to review how the proposed ACT agreement is shaped. The States of Alabama and Georgia have an obligation to assess how the last three years of drought would have been managed under the proposed agreement guidelines and to advise stakeholders of the results. If results do not meet criteria, then adjustments should be made in the operating parameters to ensure required flows are met.