Drought Effects on the Tennessee River

Barbara Martocci of the Communications staff at TVA sent out this very informative article about the effects of our drought on the Tennessee River system. No doubt, if you were on our local rivers and lakes this weekend, these effects will sound familiar. This drought is reaching levels they we have not seen locally in quite some time. The full length article is listed below.


Effects of Dry Weather on the
Tennessee River System
The five-month period from January through May of 2007 was the driest such period in 118 years. Average rainfall in the Tennessee Valley above Chattanooga has been only 11.6 inches or 51 percent of normal.
Exposed shoreline and sandbars will impact boaters this summer due to the continuing dry conditions.
The long-term forecast is for continued dry conditions.
Since February, TVA has been operating the river system in conservation mode releasing only enough water to provide the minimum flow needed to protect water quality and meet other water-supply needs. This is to ensure as much water as possible is available to fill reservoirs to recreation target levels, as well as to provide other benefits Valley citizens have come to depend on.
Because of the dry conditions, most tributary reservoirs are significantly below their recreation target levels, typically met on June 1. On average, reservoirs in the eastern Tennessee Valley were about 10 feet below where TVA would like them to be by June 1.
Although water levels are low, they are nowhere near the driest historical levels. There are two reasons for this:
1) Operating the river system in conservation mode.
2) TVA changed its operating policy in 2004 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.
Runoff 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 usually seen only when the Valley experiences the remnants of a summer hurricane to raise tributary reservoirs significantly.
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.
Recreation
As water levels on the tributary reservoirs remain lower than normal, boaters may encounter more hazards. Sandbars could be exposed, and tree stumps could be closer to the surface.
Some boat docks may be in much shallower water or dry.
It is possible that users of tributary reservoirs will continue to see the mud flats that are typical during winter reservoir drawdowns throughout the summer.
TVA is continuing to review water availability in reservoirs with flow commitments for whitewater recreation. Recreation releases on the Hiwassee River were reduced for several weeks but returned to normal last weekend. At this time, TVA does not anticipate further reductions in recreation releases.
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 in mid to late summer.
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. Some municipalities have asked citizens to conserve water use to ensure there is enough water for the rest of the summer.
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 is generating 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 May was only 54 percent of normal.
Hydropower is TVA’s cheapest source of electricity generation. TVA may need to purchase more expensive power from other power suppliers if the hot, dry weather continues.
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.
Contributed by Barbara Martocci, Communications