February 2011 Reservoir System Update
Tennessee Valley Authority (TVA)
The Eastern Valley received 2.55 inches of rain in January, which is about two inches below normal.
Runoff (the amount of water that reaches the river system when it rains instead of being absorbed into the ground) was just over an inch below normal.
The cumulative deficits for the past two months are 4.64 inches of rainfall and 1.38 inches of runoff.
As the chart below shows, most of the large tributary storage reservoirs were very close to their seasonal flood guide elevations on Feb. 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
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 above sea level—compared to its normal winter flood-damage-reduction level of 1668—as part of a project to rehabilitate the 79-year-old dam. Get an update on this project below.
Reservoirs along the main Tennessee River—Fort Loudoun, Watts Bar, Chickamauga, Nickajack, Guntersville, Wheeler, Wilson, Pickwick, and Kentucky—were all within or close to their normal operating zones at midnight on Feb. 1.
Hydroelectric power generation
When will my reservoir start going back up?
Why does TVA lower reservoir levels so far in winter?
History provides clear evidence of this pattern. During the past 140 years, the largest flood events along the Tennessee River occurred in March 1867, February-March 1875, April 1886, March 1897, March 1917, January-February 1957, March 1963, March 1973, April 1977, May 1984, February-March 1994, April 1998 and May 2003.
Reservoirs are drawn to their lowest level by Jan. 1 to provide the water-storage capability needed to reduce flood damage from such storms.
Wouldn’t it be a good idea to hold on to some of the rain we get in winter to help fill reservoirs to summer levels?
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