Dry Weather and Effects on the Tennessee River System

October 2007

The nine-month period of January through September 2007 was the driest such period in 118 years. Average rainfall in the Tennessee Valley above Chattanooga has been only 23 inches — or 58 percent of normal.

TVA has been operating the river system in conservation mode since February to ensure as much water is available to fill reservoirs to recreation target levels and provide other benefits Valley citizens have come to depend on.

Because of the dry conditions, most tributary reservoirs did not meet their targeted recreation levels this summer. On average, reservoirs in the eastern Tennessee Valley were about 10 feet below where TVA would like them to be by June 1.

In 2004, TVA changed its operating policy to allow increased winter reservoir levels on most tributary projects. This change allowed more water to be in the reservoirs at the start of 2007. This, along with operating the system in conservation mode, means that although water levels are low, they are nowhere near the driest historical levels.

Runoff, or the water that reaches the river after a rainfall, is less in the spring and summer months when growing plants absorb more water, thus less water reaches the river system.

At this point, it would take several sustained, soaking rains - the kind we usually only see when the Valley experiences the remnants of a summer hurricane - to raise tributary reservoirs significantly.

The long-term forecast is for continued dry conditions.

Some effects that reservoir users will see as the dry weather continues are described below. More information, including current reservoir water levels, predicted levels for the next three days, and observed rainfall and runoff, is available at www.tva.com/river.

Water Quality

TVA is providing water flows below dams to maintain water quality and protect aquatic habitat.

These minimum flows will continue to be maintained, however, this means that more water will have to be released from the already lower-than-normal upstream reservoirs.

Dissolved oxygen, necessary for aquatic life, is being monitored on the reservoirs throughout the river system. Due to low water flows, dissolved oxygen amounts are lower than normal on some reservoirs. TVA is examining opportunities for special dam operations that might help improve conditions on a reservoir-by-reservoir basis, but options appear very limited with so little water available.

Prolonged continuous low flows could cause cumulative water quality impacts.

Water Supply

Although TVA operations have no effect on groundwater, localities and individuals that depend on groundwater (wells) and springs for water supply may be at increased risk for impacts to water supply due to the ongoing dry weather and continuing drops in the water table.

TVA is continuing to manage river flows to keep water levels above municipal and industrial water intake structures.

Due to increased demands placed on municipal water treatment systems, some municipalities with limited treatment capacity are asking customers to conserve water to ensure there is adequate treated water to go around during the ongoing drought conditions. A number of states also are urging voluntary conservation or mandatory restriction in water use.

TVA is facilitating weekly teleconferences with representatives from state and federal agencies to discuss current drought conditions and anticipated impacts and to coordinate mitigation measures.

Hydropower Generation

Hydropower generation has been reduced significantly due to the dry conditions. TVA generates as much power as possible with the water released to meet minimum flow requirements, but due to the low rainfall, hydropower generation for January through September is only 58 percent of normal.

Hydropower is TVA’s cheapest source of electricity generation. TVA has purchased more expensive power from other power suppliers due to the hot, dry weather continuing.

Navigation

To date, commercial navigation on the Tennessee River system has not been affected significantly by the dry conditions.

Water levels in the main Tennessee River are near normal levels as TVA continues to meet the flow commitments adopted as a result of the Reservoir Operations Study.

TVA is working closely with both the U.S. Army Corps of Engineers and the towing industry to identify and address potential navigation issues on the Tennessee, Cumberland, and lower Ohio Rivers associated with the continued dry weather.