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February 4, 2011

In this issue:

Rain and runoff
Reservoir elevations
Hydroelectric power generation
Answers to frequent questions about February reservoir operations
Reservoir operations for water quality and aquatic habitat
Blue Ridge Dam rehabilitation project update
More TVA information

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 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.

 

Reservoir elevations

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.

Tributary Reservoir Elevations¹

Feb. 1, 2011
Observed Elevation

Feb. 1
Flood Guide
Elevation2

South Holston

1708.3

1708

Watauga

1952.3

1952

Cherokee

1045.5

1045

Douglas

954.9

954

Fontana

1653.6

1653

Norris

1000.6

1000

Chatuge

1918.2

1918

Nottely

1761.9

1762

Hiwassee

1486.1

1485

Blue Ridge

1623.1

1669.3

Tims Ford

876

875.5

Normandy

864.7

864

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 winter flood-damage reduction levels.

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

Conventional hydroelectric power generation was 74 percent of normal in January due to the continued dry conditions. Dry weather impacts hydroelectric power generation because hydro plants are “fueled” by water flowing through the dam.

 

Answers to frequent questions about winter reservoir operations

When will my reservoir start going back up?
The spring fill typically begins in mid-March. Most reservoirs fill to their highest level by June 1. You can track your reservoir’s elevation from TVA’s Reservoir Information page and see how it compares with the expected operating range and actual pool levels for the same date last year.

Why does TVA lower reservoir levels so far in winter?
The risk of flood-producing storms in the TVA service area is highest in winter and early spring. Summer storms typically affect only a portion of the region, but winter storms can cover the entire region for several days, with one storm followed by another even larger storm three to five days later. Plus, winter storms produce more runoff than summer storms. In summer, a lot of the rain is absorbed by the dry ground and vegetation instead of flowing into the reservoir system. But in winter and early spring, most of the rain ends up in the reservoir system.

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?
Although holding on to extra rain could help the spring fill, TVA must be very careful about going above winter flood-guide elevations because of the risk of flooding associated with winter and spring storms.

As spring approaches, TVA looks at the possibility of storing more water in the tributary system to help reach June 1 levels. But holding extra water in reservoirs already at flood-guide levels isn’t an option. If we were to go above flood-guide levels, there would be an increased risk that we would not have the storage space we would need in the event of a major winter storm. To provide the flood-reduction benefits that TVA’s system of dams and reservoirs were built to provide, we have to be prepared to deal with a flood before it occurs.

Can low water levels this time of year affect the spring spawn?
Low water levels don’t impact the success of the crappie and bass spawn in the spring, but fluctuating water levels can cause problems. Sometime between mid-April and the end of May, when the water temperature rises to between 59 degrees and 75 degrees Fahrenheit, bass and crappie lay their eggs in nests in shallow water. About the same time, water levels throughout the TVA system usually are on their way up as reservoirs are allowed to fill as the risk of flooding decreases. The levels in individual reservoirs may go up and down several times as the spring fill is temporarily interrupted to meet other water-management objectives. Rising water can affect spawning success by causing some fish to abandon their nests, and falling water can leave eggs stranded above the water line where they will dry out and die.

To avoid these impacts, TVA works with volunteers on several reservoirs to keep close tabs on water temperatures. When the temperature reaches 65 degrees at a depth of 5 feet, TVA tries to hold the water level as steady as possible for two weeks – from the time the eggs are laid until the young fish are able to leave the nest. Occasionally, very large flood events can cause an increase in reservoir elevations during the spawn. Usually this isn’t a problem, because individual reservoirs warm at different rates, and the system is large enough to give TVA some operating flexibility.

When will TVA begin providing scheduled releases for whitewater rafting?
TVA provides scheduled releases from eight TVA dams so that rafting enthusiasts can count on the availability of whitewater. For most dams, these releases begin in May. Release schedules for the 2011 rafting season will be posted on TVA’s Recreation Releases website later this month.

When do TVA campgrounds open?
TVA’s 11 seasonal campgrounds on reservoirs throughout the Tennessee River Valley will open March 18. Watch for details on TVA’s Camping and Recreation Areas website soon.

 

Reservoir operations for water quality and aquatic habitat

This article concludes our series on the many ways the Tennessee River system touches our daily lives. See previous issues for information about the benefits of river transportation, flood-damage reduction, hydropower generation, water supply, and recreation.

TVA does not have regulatory authority to control water pollution, but water quality and aquatic habitat are important considerations in operating the dams and reservoirs that make up the Tennessee River system.

TVA operates the river system to meet reservoir-specific and system-wide flow requirements that help protect water quality and aquatic habitat by ensuring an adequate flow of water. Flow requirements help to keep the riverbeds downstream of dams from drying out when generation is shut off. They also help to avoid the stagnant conditions which can occur during hot, dry weather; keep temperatures at power plants within permit limits; and protect the capacity of rivers and reservoirs to receive industrial wastewater.

TVA has installed a variety of equipment at its dams to aid in maintaining a continuous flow of water downstream. At some locations, TVA “pulses” the hydro turbines at regular intervals throughout the day or uses small hydropower units installed at a number of its dams for use when the main turbine is not operating. At other dams, TVA has installed weirs which operate like small dams, holding back some of the water when power is being generated and then slowly releasing it when generation stops.

TVA also has installed special equipment at its dams to provide the oxygen needed by aquatic life in the area downstream from the dam (called the tailwater).

Like most dams built in the 1930s and 1940s, the intakes at TVA dams were designed to draw water from deep beneath the surface of the upstream reservoir where oxygen levels drop during the late summer and early fall due to thermal stratification. Water near the surface warms and stops mixing with the heavier colder water near the bottom. Without access to the surface and atmospheric oxygen, the deeper colder water becomes oxygen deficient. When this water passes through the dam, it affects oxygen conditions and aquatic life downstream.

TVA uses a variety of technologies to address this problem. At some dams, TVA has installed equipment to improve the turbine’s ability to draw air into the waters or to inject compressed air into the water at various stages of the generation process. At other dams, TVA adds oxygen to the water before it is released through the dam by using huge, slow-turning fans to push oxygenated water from the reservoir’s surface down to the level of the turbine intake or by bubbling oxygen into the water through ordinary, garden-variety soaker hose laid on the reservoir bottom upstream of the dam. At other sites, TVA has installed weirs across the river channel below the dam, which adds oxygen to the water as it plunges over the top of the structure, much like a natural waterfall.

Studies show that flow and dissolved oxygen improvements at TVA dams have resulted in an increase in the number and diversity of fish and insects and a significant growth in tailwater fishing, which aids local economies.
TVA also conducts a variety of special reservoir operations that benefit fish. Each spring, for example, priority is given to holding reservoir levels steady for a two-week period when bass and crappie come into the shallows to lay their eggs. In addition, flows are frequently provided, or releases restricted, to facilitate fish sampling, special studies, fish stocking, and other activities.

Since 1992, TVA has provided releases from Watts Bar Dam every spring to benefit downstream sauger production. In 2008, TVA also began adjusting releases from Tims Ford Dam in order to protect the diversity of native aquatic life in the tailwater. The goal is to provide the seasonal temperature ranges suitable for trout immediately below the dam, transitioning to temperature ranges suitable for boulder darters (an endangered species of fish), several species of endangered mussels and other warm-water species downstream. Other efforts have focused on enhancing cold-water trout fisheries below Normandy, Norris, South Holston, Wilbur, Blue Ridge, and Chatuge Dams and below the powerhouse at Apalachia.

Read more about TVA tailwater improvements and other programs to protect water quality, including reservoir monitoring, watershed protection and improvement, fish population studies, and clean boating.

Fast facts

  • TVA has installed equipment at 15 dams to add life-sustaining oxygen to the water released into the tailwater at 16 projects.
  • TVA’s efforts to improve conditions in the tailwaters below its dams is one of 281 efforts recognized by the Wildlife Habitat Council for their benefits to wildlife habitat. The Wildlife Habitat Council is a nonprofit organization dedicated to increasing the quality and amount of wildlife habitat on corporate, private and public lands.
  • There are more species of fish, insects, mussels, snails, plants, and other forms of life in the Tennessee River Valley than anywhere else in North America.


Workers inspect the penstock’s structural integrity at the Blue Ridge Dam Rehabilitation Project  (click here to see a high resolution image)

Blue Ridge Dam rehabilitation project update

The Blue Ridge Dam rehabilitation project continues to safely move forward. Workers have opened  the penstock from above, allowing for increased demolition of the existing penstock before installing a new penstock liner.  Work to stabilize the dam’s intake tower and improve the dam’s upstream face also continues.

“We make progress daily and are still scheduled to raise reservoir levels at Blue Ridge in early April,” says Blue Ridge Project Manager Jeff Brown. “We continue to evaluate the work ahead of us and focus on the safety of our workers, our river neighbors and the environment.”

 


Get more information on TVA.com

The links below will take you to reservoir-related information on TVA’s website.

TVA’s reservoir operating policy:  Learn how TVA manages the flow of water through the Tennessee River system to provide navigation, flood damage reduction, power supply, water quality, water supply, recreation, and other benefits.

Reservoir information:  Get detailed information about individual reservoirs, including observed and predicted elevations and releases at TVA dams, reservoir operating guides, water quality improvements, fish population survey results, and more.  To check reservoir information from your cell phone or other mobile device, go to http://m.tva.com.

Rainfall and stream flows:  Get the latest information on daily rainfall and stream flows across the Valley.

Recreation release schedules:  View the 2010 schedule for water releases for rafting, kayaking, and canoeing below these TVA dams:  Apalachia, Ocoee No. 1, Ocoee No. 2, Ocoee No. 3, Norris, Watauga/Wilbur, and Tims Ford.

Map of TVA reservoirs and power plants:  Our interactive map is your guide to the entire TVA power system, including fossil and nuclear plants, dams and reservoirs, and visitor centers.  You’ll find interesting facts about each facility and learn how they work together for the purposes of power supply, river management, and economic development.

Water supply FAQs:  Get answers to frequently asked questions about obtaining a water intake permit, improving water quality around intakes, inter-basin transfers, and more.

Dangerous areas around TVA dams:  If you like fishing or enjoy swimming and boating on TVA-managed reservoirs, you need to be aware of the possible hazards around dams, locks, and powerhouses.

How to lock through:  Find out what you need to do to safely approach a navigation lock, secure your boat in the lock chamber, and exit the lock.

Reservoir health ratings:  See the latest monitoring results for TVA-managed reservoirs.

Campgrounds and day-use areas:  Get information here about campground fees and amenities as well as picnic pavilion reservations.

TVAkids.com:  TVA’s got a Web site just for kids!  Learn about how TVA makes electricity, reduces flood damage, protects wildlife, and more.  There’s a section for teachers, too.

TVA Heritage:  Read about the people who founded TVA, shaped its purpose, and built its power plants.  TVA Heritage offers fascinating glimpses of the agency’s 76-year history.

Get more information by phone

For the latest information on reservoir elevations and stream flows, call TVA’s Reservoir Information Line from a touch-tone phone:

  • From Knoxville, TN:  865-632-2264
  • From Chattanooga, TN:  423-751-2264
  • From Muscle Shoals, AL:  256-386-2264
  • From all other locations:  800-238-2264 (toll-free)

For answers to questions on how your reservoir is operated, call TVA River Operations at 865-632-6065.

For answers to questions about recreation, permitting procedures, reservoir land management plans, and other environmental issues, call TVA’s Environmental Information Center at 1-800-882-5263.

 
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