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January 4, 2011

In this issue:

Rain and runoff
Reservoir elevations
Hydroelectric power generation
Answers to frequent questions about winter reservoir operations
Reservoir operations for recreation
Blue Ridge Dam rehabilitation project update
TVA’s Raccoon Mountain Trail System Garners National Award
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 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.

Eastern Valley Rainfall

Month

Observed rainfall

Normal rainfall

Percent of normal

January

4.51

4.6

98

February

2.68

4.23

63

March

2.79

4.82

58

April

2.69

4.17

65

May

4.50

4.23

106

June

2.91

4.28

70

July

3.96

4.97

80

August

4.01

4.28

94

September

3.68

3.38

109

October

2.89

2.99

97

November

5.31

3.51

151

December

1.86

4.45

42

2010 total

41.80

50.06

83

 

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.

Tributary Reservoir Elevations¹

 

Jan. 1, 2011
Observed Elevation

Jan. 1
Flood Guide
Elevation2

South Holston

1708.1

1708

Watauga

1951.7

1952

Cherokee

1044.7

1045

Douglas

954.1

954

Fontana

1652.5

1653

Norris

1000.1

1000

Chatuge

1918.1

1918

Nottely

1761.9

1762

Hiwassee

1485.7

1485

Blue Ridge

1624.8

1668

Tims Ford

873.6

873

Normandy

863.9

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 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 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 their normal operating zones at midnight on Dec. 31, but went above those zones due to heavy rain on New Year’s Day. Releases are being scheduled to return these reservoirs to their normal ranges as efficiently as possible.

 

Hydroelectric power generation

Conventional hydroelectric power generation was a little higher than normal in December due to heavy rain in late November. TVA released as much of the excess water as possible through the hydroelectric turbines at its dams in the process of recovering space in Valley reservoirs to store the water from future storms, which reduced the need for more expensive generation.

Total conventional hydro generation for 2010 was 86 percent of normal due to 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

Why does TVA lower reservoir levels so far in winter?
The risk of flood-producing storms in the Tennessee Valley is highest in winter and early spring. Summer storms typically affect only a portion of the Valley, 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.

How low will my reservoir get this winter?
To see the expected winter elevation range for your reservoir, go to TVA’s Reservoir Information page and then click on the down arrow in the “Select a reservoir” box. Choose a reservoir from the drop-down list and click on the “View info” button. You’ll see a page with current operating information for that reservoir. Click on the “Operating guide” link on the right side of the page.

If you’ve selected a tributary flood-storage reservoir, you’ll see a graph with a gray band labeled “Expected elevation.” Based on computer simulations using more than 100 years of historical rainfall and runoff data, you can expect your reservoir to be in the shaded area an average of eight out of 10 years on any given date. For main-river reservoirs, look for the shaded band labeled “Normal operating zone.”

How was the winter flood guide level on my reservoir determined?
How far a reservoir is drawn down to get ready for wintertime storms varies depending primarily on the reservoir’s original flood-storage allocation, or on the amount of space determined to be necessary to store enough water to reduce downstream flooding. The engineers who designed TVA’s water-control system determined the flood-storage allocation for individual reservoirs based on their drainage area, size and shape, historical rainfall data, and other variables that influence a reservoir’s ability to store and release water at given times of the year.

Some of these flood-storage allocations have been modified over the years based on analyses of rainfall and runoff characteristics of the drainage basin and physical limitations of the reservoir system. The most recent analysis, completed in 2004, resulted in a decision to allow higher winter water levels on the 11 tributary reservoirs that supply the bulk of TVA’s flood-storage capacity. On average, winter pool levels on these reservoirs are 10 feet higher than they would have been given the same weather conditions under TVA’s previous operating policy.

Why are some reservoirs lower than others this time of year?
If the level of your reservoir seems lower than that of a neighboring reservoir, it could be because there was more rain in the watershed of the other reservoir. It may not have rained in your area, but it might have rained a lot just a short distance away. Reservoir elevations are highly dependent on local rainfall and runoff.

Another possibility is that you are comparing two different types of reservoirs. Large tributary reservoirs fluctuate the most because they do the bulk of the work in controlling floods. They must be drawn down more aggressively because they have more storage capacity than other reservoirs due to their size and shape. Main-river reservoirs don’t fluctuate nearly as much because they have less storage space and because of navigation requirements.

Other reservoirs are maintained at near-steady levels year around. These reservoirs are operated primarily to maximize power production or provide local benefits. How your reservoir is operated depends on how it was designed and its purpose within the entire system.

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.

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. Again, 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.

Lately, it seems as though TVA is generating every time I want to do some tailwater fishing. Why is that?
Hydro generation picks up after Labor Day weekend as TVA begins the annual unrestricted drawdown to Jan. 1 flood guide levels. Anglers can also expect increased generation as TVA prepares for and moves the water from major winter storms.

To get the latest water release schedules for TVA dams, go to TVA’s Reservoir Information page and then click on the down arrow in the “Select a reservoir” box. Choose a reservoir from the drop-down list and click on the “View info” button. You’ll find information on observed and predicted releases, as well as observed and predicted water levels upstream and downstream of the dam.

Water release schedules also are available by calling TVA’s automated reservoir information line: 865-632-2264 in the Knoxville area; 423-751-2264 in the Chattanooga area; 256-386-2264 in the Muscle Shoals area; and 1-800-238-2264 from all other locations. If you are hearing-impaired, call 1-800-438-2264. An automated recording will guide you to the information you need. Get detailed information about obtaining reservoir information by phone.

Water release schedules are updated periodically throughout the day. Next-day release schedules are usually available by 6 p.m. of the current day.

 

Reservoir operations for recreation

This article continues our series on the many ways the Tennessee River system touches our daily lives. In previous issues, we talked about the benefits of river transportation, flood-damage reduction, hydropower generation, and water supply. In our next issue, we’ll highlight benefits to water quality and aquatic habitat.

Mention the word “recreation” in discussing TVA reservoir operations and most people think of boating, fishing, and swimming on their favorite lake. But recreation below TVA dams is an equally important consideration in operating TVA’s reservoir system.

Managing the river system to support a broad range of recreational uses can be a challenge, says David Bowling, manager of TVA’s River Forecast Center. “Most people understand that there’s a balancing act involved in keeping reservoir elevations up for recreation while maintaining sufficient storage space for flood-damage reduction and providing the water needed to meet navigation, power generation, water quality and other demands. But it doesn’t end there. Sometimes, we also have to make tradeoffs when it comes to managing water releases for different recreational uses. In dry years, for example, providing the flows needed for whitewater recreation below TVA dams can impact water levels above the dam, which affects reservoir recreation. Also, providing flows for rafting, paddling, and other kinds of whitewater recreation can interfere with tailwater fishing, which depends on minimum flow.”

Bowling explains how TVA operates the river system to support all of these recreation activities below.

Reservoir recreation
“Low water levels can make access points on tributary reservoirs unusable, force boat dock and marina operators to move their floating facilities, impact boating safety, and detract from a reservoir’s scenic beauty. TVA restricts the drawdown of tributary storage reservoirs during the summer to reduce these impacts.

“From June 1 through Labor Day, the goal is to keep tributary reservoirs as close to their flood guide elevations as possible. Flood guide levels set an upper bound for reservoir elevations year-round because they ensure we reserve enough space to store potential flood waters. But in summer, this upper bound is also the target level. We restrict water releases in order to keep tributary reservoirs as close to their flood-guide elevations as possible in order to provide higher elevations for reservoir recreation.

“TVA also considers reservoir fisheries in its operation of the river system, which is important to anglers. 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. It’s especially important to avoid stranding the eggs above the water line where they would dry out and die.”

Tailwater recreation
“A growing number of people are interested in tailwater recreation—whitewater rafting, canoeing, and kayaking in the area downstream from TVA dams. To support these recreation activities, TVA provides scheduled releases from eight TVA dams so that paddlers can count on the availability of whitewater. We sit down with rafting company representatives and state officials every year to hammer out a schedule of days and hours of guaranteed releases. For most dams, these releases begin in May and end in September or October.

“We also support tailwater fishing through our operation of the river system. We’re committed to providing sufficient flow to support fish and other aquatic life below our dams, and we’ve invested millions of dollars in equipment designed to improve dissolved oxygen concentrations in tailwater areas. In addition, flows are frequently provided, or releases restricted, to facilitate fish sampling, special studies, fish stocking, and other activities. For example, since 1992, we’ve provided releases from Watts Bar Dam every spring to benefit downstream sauger production. Other efforts have been focused on enhancing cold water trout fisheries below Normandy, Tims Ford, Norris, South Holston, Wilbur, Blue Ridge, and Chatuge Dams and below the powerhouse at Apalachia.”

Editor’s note: View recreation release schedules and learn more about tailwater improvements.

Fast facts

  • More than 13,000 boaters take advantage of the locks along the Tennessee River waterway each year to travel from one section of the Tennessee River to another.
  • In 2010, TVA released water for whitewater recreation on 124 days at Apalachia Dam, 114 days at Ocoee #2 Dam, 94 days at Watauga/Wilbur Dams, 56 days at Norris Dam, 34 days at Ocoee #3 Dam, 33 days at Tims Ford Dam, 33 days at Upper Bear Creek Dam, and 27 days at Ocoee #1 Dam.
  • An estimated 74,000 people floated the Hiwassee River in 2010.
  • Water-based recreation in the Tennessee Valley generates about $2 billion in revenue annually


Blue Ridge Dam rehabilitation project update

More than 500 area residents had a chance to learn about TVA’s progress in rehabilitating Blue Ridge Dam and get answers to their questions at a Community Day event hosted by TVA on Dec. 11, 2010.

The latest milestone for the project is the completion of the soldier pile wall. This wall, which holds back the soil at the construction site, had to be completed before workers could begin excavating down to the penstock. Excavation to the penstock is currently underway.

Inside the penstock, workers have removed the bulging section of the steel liner and begun the process of demolishing a huge (one-foot thick, 172-feet long) concrete support beam.

Work to repair and stabilize the upstream face of the dam also is proceeding smoothly. Workers have finished replacing the riprap on the bottom third of the dam and have begun putting down a layer of course sand on the middle section.

View pictures, read more information about the Blue Ridge Dam rehabilitation project, and sign up for regular e-mail updates.

 

TVA’s Raccoon Mountain Trail System Garners National Award

TVA and the Chattanooga chapter of the Southern Off-Road Bicycle Association received the 2010 National Partnership Award from American Trails for their work on the Raccoon Mountain trail system near Chattanooga.

The 17-mile trail system encircles a 528-acre reservoir supporting TVA’s Raccoon Mountain Pumped Storage generating plant. The trails have become a popular destination for hikers and mountain bikers from around the region.

The award from American Trails, a nonprofit organization that works to protect and enhance the nation’s network of trails, recognizes partnerships that have benefited agencies or services within the field of trail planning, design or implementation and have contributed to a positive public experience.

The Chattanooga chapter of the Southern Off-Road Bicycle Association led and managed the trail work on Raccoon Mountain, and TVA conducted an environmental review to be sure a trail could be created that would protect the environment. TVA biologists, archaeologists, recreation specialists and others evaluated the potential impact on the forested land area. TVA continues to provide assistance on future trail development plans.

The Southern Off-Road Bicycle Association works to promote land access, trail preservation and new trail development in the Southeast. Staff and volunteers provide training for builders to create trails that prevent erosion as well as promote “Leave No Trace” policies with outdoor enthusiasts to reduce their impact on the environment.

“Recreational pursuits by TVA, such as the Raccoon Mountain trail system, encourage the use of properly managed, eco-friendly dispersed recreation on public lands,” says Anda Ray, TVA senior vice president of Environment & Technology. “This aligns well with TVA’s Environmental Policy, which includes enhancing public benefits of the Tennessee Valley’s land and water resources – making it a better place to live, work and play today and for future generations.”

Erik Rippon, vice president of the Chattanooga Chapter of the Southern Off-Road Bicycling Association, says the chapter would like to thank TVA for the opportunity to build this trail system for the local community.

“The partnership formed years ago by TVA and Southern Off-Road Bicycle Association’s Chattanooga chapter has resulted in the construction of a true gem for the Chattanooga outdoor community and will hopefully become a model for other Southern Off-Road Bicycling Association chapters regionally,” he says.

The Raccoon Mountain trail system includes trails for novices and experts. Multiple mountain-biking and trail-running events occur on weekends during the spring, summer and fall months. Events have included the Southeast Regional Championships, with more than 300 racers, and the Scenic City Trail Marathon, with more than 200 runners. The trails have been recognized in two national mountain bike publications, “Bike Magazine” and “Mountain Bike Magazine.”

This project has gained widespread support from various organizations, including the National Park Service’s Rivers, Trails & Conservation Assistance Program; Outdoor Chattanooga; the Bikes Belong Coalition; and an extensive network of volunteers.

 


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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