TVA Reservoir System Update - January 2011

TVA provides monthly updates on the operation of TVA-managed reservoirs by e-mail. To sign up for future updates, provide feedback, change your e-mail address, or have your address removed from this distribution list, please send an e-mail request to reservoirupdate@tva.com.

Rain and runoff

The Eastern Valley received less than two inches of rain in December, which is 42 percent of normal.

Eastern Valley rainfall for 2010 totaled about 42 inches, which is about eight inches below normal. Runoff (the amount of water that reaches the river system when it rains instead of being absorbed into the ground) was about three inches below normal.

For comparison, in 2009, Eastern Valley rainfall was about six inches above normal and runoff was about three inches above normal.

Reservoir elevations

As shown in the chart below, most of the large tributary storage reservoirs were very close to their seasonal flood guide elevations on Jan. 1.

Flood-guide elevations show the amount of storage allocated for water from flood-producing storms during different times of the year. TVA releases water as needed to keep reservoirs at or below their flood guide elevations to be ready for these storms. In summer, the goal is to keep reservoirs as close to their flood guide elevations as possible to support recreation while still meeting minimum flow commitments. But, in winter, reservoirs may be lower than their flood guide elevations as water in storage is used to meet winter power demands and other needs.

¹ Water elevation at the dam in feet above mean sea level
² Flood-guide elevations show the amount of storage allocated for flood damage reduction during different times of the year. The amount of storage varies with the potential flood threat. Flood-guide elevations are lowest from Jan. 1 through mid March because winter storms are generally larger, occur more frequently, and produce more runoff. Flood-guide elevations increase between mid-March and June 1 as the risk of flooding decreases. They are highest from June 1 through Labor Day to support summer reservoir recreation. After Labor Day, TVA begins the unrestricted drawdown to Jan. 1 flood-guide elevations.

Blue Ridge Reservoir is a special case. TVA began a deep drawdown on Blue Ridge in mid-July 2010. The reservoir is being held at an elevation between 1620 and 1630 feet abov

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