December rainfall puts basin into flood storage; sets record for Thurmond

This December, the Savannah River Basin received above-average rainfall at all three Corps of Engineers reservoirs. Excess rainfall filled the reservoirs past their “summer full pool” levels and into a portion of their flood storage space. A new record was also set for December rainfall in the Thurmond sub-basin.

We recorded 8.5 inches of rain in the Thurmond sub-basin this December. That’s 220 percent of what’s considered “normal” rainfall for the month. This is the wettest December on record for the Thurmond sub-basin, since we started recording data in 1948. The second wettest December on record for Thurmond was in 1953 with 8.35 inches.

This December we recorded 7.9 inches of rain in the Russell sub-basin (197 percent of normal) and 8 inches in the Hartwell sub-basin (156 percent of normal). In the last week of December the entire basin recorded 400 percent of normal rainfall, pushing reservoir levels above summer full-pool into flood storage.

RainfallBarGraphDec

Current Basin Conditions:

As of this writing (Dec. 31), the current elevations are:

  • Hartwell 661.7 ft-msl (5.7 ft above winter guide curve, 1.7 ft above summer full pool)
  • Russell 476.3 ft-msl (1.3 ft above guide curve/full pool)
  • Thurmond 333.3 ft-msl (7.3 ft above winter guide curve, 3.3 ft above summer full pool)

Reservoir levels are now beginning to stabilize. Over the next several weeks, our water managers will increase releases from the Thurmond Dam to bring the Thurmond reservoir out of flood storage. During that time, we expect releases at the Hartwell and Russell dams to remain relatively constant. Starting Jan. 1, daily average outflows from the Thurmond Dam are scheduled for 25,000 cfs.

When the Thurmond reservoir approaches 330 ft-msl, we plan to increase outflows at the Hartwell and Russell dams to evacuate flood storage in those reservoirs. We are targeting an elevation of 658 ft-msl at Hartwell and 328 ft-msl at Thurmond (two feet below full summer pool) by late January so we can reach the winter “guide curve” elevation during the typical winter re-fill period.

However, our water managers and power plant operators carefully manage outflows to make the most efficient use of the water through hydropower production.

Weather forecasts suggest the possibility of receiving up to one inch of rain basin-wide in the next seven days. We are carefully monitoring conditions around the clock and will adjust operations as necessary.

As always, projections are subject to change based on unforeseen weather events. For the most up-to-date data on lake levels, water management, or rainfall, visit our water management site at http://water.sas.usace.army.mil.

Impacts of December Rainfall on Winter Drawdown

December ranked the second wettest month of 2013 for the Thurmond and Russell sub-basins, due to heavy rain in the middle portion of the basin. It was the fourth wettest month of the year at Hartwell.

Above average rainfall resulted in a dramatic rise in lake levels throughout the month. Hartwell reached full summer pool (660 feet per mean sea level) Dec. 9 and gradually increased to 1.7 feet above full summer pool by the end of the month. Thurmond Lake reached full summer pool (330 ft-msl) on Dec. 24 and increased to more than 3 feet above full summer pool by the end of the month.

Most of December’s rainfall occurred during intense isolated rain events that dumped between 1 to 2 inches of rain in less than 24 hours.

For example, on Dec. 22 and 23, a rain event brought 3.2 inches of rain to the Thurmond sub-basin. That rainfall and the subsequent run-off brought up the lake level more than 2 feet. Another rain event occurred Dec. 28 and Dec. 29, which brought an additional 2.3 inches of rain to the Thurmond sub-basin, yielding inflows as high as 50,000 cubic feet per second (cfs) for that period. That additional rain event further increased the lake level by more than two feet. Hartwell and Russell also experienced similar rain events with related spikes in lake levels.

The December rainfall demonstrated how quickly the reservoirs respond to moderate rainfall during this time of year. In colder conditions with saturated soil, nearly all rainfall turns into runoff, yielding approximately one foot of lake-level rise for every inch of rain. This is one reason that justifies the conventional wisdom of a “winter drawdown.” Another few moderate rain events of this type in succession can quickly put water managers in the flood-fighting mode.

While we had originally planned to reach a four-foot winter drawdown this winter, excess rainfall kept reservoir levels higher than guide curve. Rainfall throughout the end of November, combined with December rainfall, contributed to the overall trend of a wet 2013.

We welcome your questions and comments in the “comments” section below.

~ Tracy Robillard and Russell Wicke, Corporate Communications Office

 

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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  • yu nah ee tah

    I am not complaining.

    I left a good job in the city, I worked for the man nearly night and day, then I never forgot the good times on the river so I just had to be free.

  • Jay

    The info provided clearly supports the fact that there is NO NEED for a winter draw down. This was the wettest Dec in history, which capped off one of the wettest years of record for this region. Yet Hartwell is only 1.7 feet beyond summer full pool with plenty of flood storage remaining. Thurman is higher but only slightly and also has plenty of storage left. December dropped 200%the of normal rain onto a completely saturated ground and still well within the lake system’s operating parameters. This has been a once in a lifetime wet period for the lake and it has survived. It stands to reason than a wet year of this magnitude will remain well outside the relm of normal… so why have a drawdown? There is clearly no need. Recent posts by the Corp have hented at a need for a lower summer full pool level. That is simply absurd. Keep the lakes full. Let people as well as wildlife enjoy them. Stop over taxing and exploiting them for the benefit of big business and politics.

    • yu nah ee tah

      Jay

      I like a man who speaks his mind in plain English that everyone can understand. You should run for some office, Other elected officials could learn from your God given common sense approach to this hitherto unnecessarily complicated issue.

      If you come down to the river
      I bet you gonna find some people who live
      And you don’t have to worry if you got no money
      People on the river are happy to give

      I also agree with Barry for that matter. I am going to be more better agreeable in ’14.

      Rollin’ on dariva

    • http://www.sas.usace.army.mil/ US Army Corps of Engineers

      You have your facts wrong, Jay. The December record was limited to the Thurmond sub-basin only. (Hartwell didn’t even come close to a December record.) And even if we isolated your claim to Thurmond sub-basin, it is highly unlikely this December was the all-time wettest in history. We began documenting rainfall in 1948 and only in that sense was it a record. Also, don’t confuse the most rainfall recorded with the greatest rainfall possible. The basin-wide rainfall we received over the last couple weeks was not extraordinary. It is not inconceivable that we might have gotten several more inches in succeeding days which would have put us in a more difficult situation than we experienced in July – and July’s rainfall was only a 10-year event.

      On the contrary, these past two moderate rain events have demonstrated the necessity of a winter draw down. We are only just now entering the wettest period of the year – a time when our water manual says we should posture to receive the anticipated additional rainfall by lowering the reservoirs 4 feet from summer full. Thurmond is more than 6 feet above what the water manual recommends and Hartwell is nearly 6 feet above. Can you imagine then what kind of difficulty we would be facing if we got our 100-year event in January or February? And supposing we intentionally disregarded the drawdown protocol before this 100-year event; I don’t imagine those who objected to the winter drawdown would be coming to the defense of the Corps at that time. We operate the way we do to protect lives and property. The projects belong to the Corps and since that is so, the lives and property impacted by the projects are rightly our responsibility. And we accept this responsibility with grave discretion.

      All this being said, the completion of the Savannah River Basin Comprehensive Study will tell us if we should adjust our water manual.

      Thanks for the comment. ~Russell Wicke

      • Ferris

        Thank you Russell, and the USACE team, for keeping all Basin users in mind! Those of us from Augusta to Clyo to Savannah who plant timber, hunt, and play in the flood zone downstream of Thurmond are very appreciative of moderate preventative release rates and are severely impacted when excessive lake storage has to be suddenly released. Yes, floods will happen. But it would be a huge mistake to ignore the decades of history that developed the Guide Curves. Having reviewed the publically available history myself, it appears that a 4 Ft winter draw down is a very good number. I look forward to the study results later this year.

        • http://www.sas.usace.army.mil/ US Army Corps of Engineers

          Thank you Mr. Ferris for your feedback, and representing the concerns of those immediately below Thurmond. ~Russell

  • barry ouzts

    Keep up with the good job you are doing. Those that use and enjoy the lake appreciate it. It is a tough job taking many different needs into consideration. If done correctly, you will never fully satisfy anyone completely. Therefore the critics will follow. It is the nature of the job. Thanks again. Barry Ouzts

    • http://www.sas.usace.army.mil/ US Army Corps of Engineers

      Thanks for the positive feedback Barry! ~Russell Wicke, Corporate Communications Officer