Drought flow rates changed in February: here’s why

Many of our stakeholders have asked why outflow at Thurmond Dam recently increased from 3,600 cubic feet per second (cfs) to 4,000 cfs. Let me answer those questions and perhaps shed some light on our operational process.

First some background:
Our water managers only have limited discretion when making operational decisions on Thurmond discharge during drought. They are bound by law to follow the Savannah River Basin (SRB) Water Manual. The Drought Contingency Plan (DCP), a part of this manual, directs discharge volumes at specific lake levels, seasons, and in some cases flow rates of the Broad River.

We understand some in the SRB community would like to see changes in the DCP – and we are open to changes. However, in order to make changes, we must follow a process outlined in the National Environmental Policy Act (NEPA).

Essentially, NEPA requires an Environmental Assessment (EA). An EA is a study that evaluates the impacts, value and risks associated with a proposed change. The EA also provides an opportunity for state and federal agencies, industry partners and the general public to review the study and submit input.

If the study demonstrates noteworthy benefits and shows impacts are mitigated or acceptable, we can make changes to the plan.

We are following this same process right now with the Comprehensive Study, which may result in changes to our current DCP.

It is also the process we went through in July 2012, which updated the DCP and gave us the plan we are following now. The table below outlines our current drought release rates:

Drought flow rates imageAnd this reveals the answer to the question: Why did we increase Thurmond outflow from 3,600 cfs to 4,000 cfs?

The answer: We are following the Drought Contingency Plan. In drought level 2 (DL2) the plan allows for a low wintertime flow of 3,600 cfs from Nov. 1 to Jan. 31, as indicated in the above table.

Beginning Feb. 1 wintertime flow ends and discharge must return to the normal DL2 flow rate, which is 4,000 cfs.

(Note: If the Broad River flow is equal to or less than its 10th percentile, the plan allows for a 200 cfs decrease in flow when in DL2. We may be able to implement that decrease soon.)

We recognize that “following the plan” is an unsatisfying answer. We ask you to keep in mind, however, that we lowered outlfows to 3,600 cfs for the same reason – we were following the approved plan.

Why does the plan call for these actions?

Colder water is better able to retain oxygen; therefore, in the winter the river maintains water quality at lower flows. We recognized this fact in the 2012 EA.

When stakeholders asked us to look at ways to better conserve water, one of the ways we improved on the previous plan was to reduce flows in winter months while in DL2 and DL3. Under the previous drought plan, we would have been releasing greater volumes this winter. The reason the plan calls for a return to normal DL2 flows in February is because the water is beginning to warm, and warm water retains less dissolved oxygen.

The changes in the 2012 EA enabled us to conserve more water this winter by flowing at 3,600 cfs, rather than 4,000 or even 3,800 cfs.

Although the plan likely has room for improvement, a great deal of research, study and input has gone into the DCP. When we make adjustments to the plan through an EA, the law requires us to remain in compliance with the changes. By following the approved plan we fulfill a commitment to all stakeholders. That commitment is to operate the system in a way that was coordinated and vetted through everyone.

The ongoing Comprehensive Study nears completion and soon we will release a draft for public review and comment. That is our next opportunity to improve the efficiency of the DCP. When we release the Comprehensive Study’s Draft EA for public review and comment, we’ll draw attention to it on this blog.

Please stay tuned here for more.

Thanks for reading.

~Russell Wicke, Corporate Communications

About US Army Corps of Engineers Savannah District

The U.S. Army Corps of Engineers Savannah District oversees a multi-million dollar military construction program at 11 Army and Air Force installations in Georgia and North Carolina. We also manage water resources across the Coastal Georgia region, including maintenance dredging of the Savannah and Brunswick harbors; operation of three hydroelectric dams and reservoirs along the upper Savannah River; and administration of an extensive stream and wetland permitting and mitigation program within the state of Georgia. Follow us on Twitter @SavannahCorps and on Facebook.com/SavannahCorps
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