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December 6, 2010

In this issue:

Rain and runoff
Reservoir elevations
Hydroelectric power generation
Reservoir operations
Managing the Tennessee Valley’s water supply
Sequoyah steam generators journey on the Tennessee River
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 more than three inches of rain the last few days of November, boosting the total rainfall for the month to 5.31 inches, which is 151 percent of normal.

For the year through Nov. 30, eastern Valley rainfall was 88 percent of normal, and runoff (the amount of water that reaches the river system when it rains instead of being absorbed into the ground) was 86 percent of 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

Total (year to date)

39.94

45.61

88

 

Reservoir elevations

As shown in the table below, most of the large tributary storage reservoirs were above their seasonal flood guide elevations on Dec. 6 due to heavy rain the last few days of November. Douglas and Fontana were nearly eight feet above their flood guide elevations.

Tributary reservoir levels will continue to drop through December as TVA moves the high inflows through the reservoir system and targets Jan. 1 flood guide elevations. Flood-guide elevations are lowest from Jan. 1 through mid March in order to provide space to store rain and runoff from winter storms, which are generally larger, occur more frequently, and produce more runoff than summer storms.

On Dec. 6, South Holston, Cherokee, Norris, Chatuge, Nottely, and Normandy were from one to six feet higher than their Jan. 1 flood guide elevations; and Douglas, Fontana, Hiwassee, and Tims Ford were from seven to 13 feet higher. Watauga Reservoir fell below its winter flood-damage reduction level at the end of August due to a lack of local rainfall.

Blue Ridge Reservoir is a special case. TVA began a deep drawdown on Blue Ridge in mid-July. 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 at or above their normal ranges on December 6.

Tributary Reservoir Elevations¹

 

Dec. 6, 2010
Observed Elevation

Dec. 6
Flood Guide
Elevation2

Jan. 1
Flood Guide
Elevation2

South Holston

1710.3

1710.8

1708

Watauga

1949.4

1952.9

1952

Cherokee

1049.2

1048.2

1045

Douglas

966.6

958.9

954

Fontana

1665.3

1657.7

1653

Norris

1005.8

1002.9

1000

Chatuge

1920.0

1918.5

1918

Nottely

1765.4

1762.9

1762

Hiwassee

1493.1

1492.2

1485

Blue Ridge

1624.5

1671.1

1668

Tims Ford

880.5

878.1

873.1

Normandy

865.1

864.8

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.

 

Hydroelectric power generation

Conventional hydro generation for the year through Dec. 6 was 85 percent of normal.  The lower-than-normal generation was due to the continued dry conditions.

Dry weather impacts hydroelectric power generation because hydro plants are “fueled” by water flowing through the dam.

Water releases increased in late November in order to recover storage space after a significant rain event. TVA is releasing as much of this water as possible through the hydroelectric turbines at its dams to maximize its value. This likely will result in increased hydropower generation through mid-December. With no rain in the forecast, however, hydropower generation is expected to decrease once TVA moves the high inflows through the river system.

As long as the dry conditions continue, TVA will limit releases with the objective of holding as much water as possible in the tributary reservoir system while still maintaining adequate flood storage space. Although this impacts hydroelectric generation in the short term, it means there is more water in storage if needed to meet peak winter power demand and puts the reservoir system in a better position to fill next spring.

 

Reservoir operations

Weather events like the one in late November keep life interesting in TVA’s River Forecasting Center, says center manager David Bowling.

“One week we were limiting releases to keep as much water in the tributary system as possible because of the dry conditions. Then suddenly we were in a flood control operation.”

On Dec. 1, TVA was spilling water at Great Falls, Chickamauga, Nickajack, Guntersville, and Pickwick in order to move water through the system as quickly as possible to recover flood storage space after a large storm system dumped two to four inches of rain across the Tennessee Valley in a 24-hour period.

Bowling says the focus in the next few weeks will be on getting reservoirs back to flood guide elevations.
“We’ll continue to release as much water as possible through the hydroelectric turbines. But where we can’t release the water fast enough through the turbines to recover the needed storage space, we’ll have to spill,” he says.

Because there is no rain in the forecast, Bowling expects reservoirs to be back at target elevations by mid-December and reach Jan. 1 flood guide elevations on schedule.

“We’ve got a lot of water to deal with in the next few weeks, but that is no guarantee that we won’t be back to operating in a water conservation mode this spring,” he says.

TVA-managed reservoirs are drawn to their lowest levels by Jan. 1 each year to get ready for flood-producing storms. These storms typically occur in winter and early spring when vegetation is dormant and runoff is highest. But Bowling says the recent rain is a good reminder of why it’s so important to maintain adequate flood storage space year-round.

“A major storm can occur any time, and we have to be ready. If we aren’t prepared to deal with the rain before it occurs, we won’t be able to provide the flood reduction benefits that TVA’s system of dams and reservoirs was designed to provide,” he says.

How far a reservoir is drawn down to get ready for wintertime storms varies depending primarily on the reservoir’s original flood-storage allocation. 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.

To see the expected winter elevation range for a reservoir, go to TVA’s Reservoir Information website 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.”

 

Managing the Tennessee Valley’s water supply

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, and hydropower generation. In upcoming issues, we’ll highlight water quality and recreation benefits.

When we turn on a faucet, we expect water to come out. When the weather warms up, we assume there’s enough water to wash our cars and keep our lawns green. We tend to take our water supply for granted here in the Tennessee Valley, and no wonder.

The Tennessee Valley get lots of rain—an average of 51 inches a year. That’s more than double the average rainfall in the southwestern United States. But we use a lot of water, too. We pump water out of the river to use in our homes, to run our factories, to make electric power, and to irrigate our farms.

In fact, the Tennessee River is the most intensively used river in the country. A recent inventory of all the current water supply extraction points within the basin indicated that more than 12 billion gallons of water are taken from the river daily. But the good news is that about 97 percent of that water is returned to the river for reuse downstream—making the Valley one of the lowest water consumers in the U.S.

Several extended dry periods in the past 25 years have brought home the fact that water is a replenishable, but not an infinite, resource, says Gary Springston, TVA program manager for water supply.

“The fact that TVA manages reservoir elevations to reduce flood damage is well known. But making the best use of the available water is an equally important responsibility in dry years. Without the TVA system of dams and reservoirs, the surface water supply would be much less reliable than it is today.”

Springston says TVA helps ensure a dependable water supply by storing water in tributary reservoirs during the spring when inflows to the reservoir system are highest, and then releasing the stored water during the summer when there is relatively little inflow into the system. “That helps provide the reservoir levels and system flows needed to support water supply withdrawals and allow pumping equipment to function properly.”

TVA also manages the reservoir system to meet minimum flow targets at all of its tributary dams and at Chickamauga and Kentucky Dams. Releases to meet these flow targets protect water quality and provide for instream uses such as aquatic habitat.

The Tennessee Valley is not immune to water shortages, however. In fact, some communities—especially communities in headwater areas of the watershed—were forced to limit water withdrawals and implement conservation measures due to low stream flows during the 2007-2008 drought. These communities generally are dependent on groundwater or unregulated streams (streams that aren’t controlled by dams for water supply) and don’t have the option of connecting to other water systems with intakes on TVA-managed reservoirs or larger rivers in the watershed.

Springston says TVA was able to protect water supplies during the 2007-2008 drought, which was one of the worst on record. But he doesn’t want people to become complacent about water-supply issues. “There’s always a possibility that future droughts could be worse. In that case, even systems connected to the Tennessee River system could face conflicts between instream flow needs to support water quality and aquatic life and withdrawals for offstream uses such as public-water supply, industry, thermoelectric power generation, and irrigation.”
Issues of concern include growing demand for water due to population growth and interbasin transfers.

“The Tennessee River watershed is surrounded by areas that will need more water to accommodate growth,” says Springston. “Blount and Cullman counties in Alabama, Alcorn and Lee counties in Mississippi, and areas in northwest Georgia are all looking to the Tennessee River to meet their future water-supply needs. These requests have the potential to impact future growth within the region, as well as other benefits provided by the system.”

What TVA is doing

The Tennessee Valley Water Partnership was formed about five years ago to address these and other water-supply issues, says Springston.

“TVA serves as host and facilitator for the Partnership, which convenes on a regular basis to look for common ground with regard to water quantity issues—all the while recognizing and respecting each state’s processes, interests, laws, and regulations.”

The group includes representatives from Alabama, Georgia, Kentucky, Mississippi, North Carolina, Tennessee and Virginia, as well as agencies such as the Environmental Protection Agency and the U.S. Geological Survey.
“Watersheds cross state lines,” says Springston. “We are dealing with natural systems that don’t follow man-made jurisdictions, and effective water supply planning has to reflect this reality. For example, drought conditions may exist throughout a particular watershed that sits astride a state line. One state has imposed water conservation measures, while the other has not. In the absence of a coordinated response to drought conditions, people living in the ‘downstream’ state may experience water shortages. Water is a shared resource, so it’s important to plan from a regional perspective.”

Springston says it’s time to assign a value to water that truly reflects its worth.

“We’re fortunate to live in a region blessed with water, but that doesn’t mean we can assume that our historically abundant supply will always be sufficient. As a region, we need to work together to plan properly for growth and be prepared for future droughts. And, as individuals, we each need to take personal responsibility for using water wisely in our daily routines.”

Cut your water use up to 35 percent with these simple steps.

Fast facts

  • Water is withdrawn at over 700 points along the Tennessee River and its tributaries to benefit approximately 4 million Tennessee Valley residents.
  • In 2005, an estimated 10,531 million gallons of water per day (mgd) were withdrawn for power plant cooling; 1,179 mgd were withdrawn for industrial use; 684 mgd were withdrawn for public supply; and 43 mgd were withdrawn for irrigation purposes.
  • Between 2005 and 2030, withdrawals for power plant cooling are projected to decrease by 12 percent due to an anticipated reduction in once-through cooling. Industrial water use (including mining) is projected to increase by 10 percent, public-supply water by 32 percent, and irrigation water use by 65 percent.
  • Surface water supplies about 98 percent of all water withdrawals in the Tennessee Valley.

 

Sequoyah steam generators journey on the Tennessee River

Four new steam generators for Sequoyah Nuclear Plant Unit 2 arrived in New OrlePicture Of Steam Generatorans from South Korea in early November and were transferred to barges for the trip to Sequoyah. The barges brought them up the Tombigbee Waterway into the Tennessee River for the final leg of their journey. The trip included passage through 18 navigation locks on the waterways.

Water transportation is the only practical method for shipping extremely large and bulky pieces of machinery or equipment. Items as varied as giant cranes for highway bridge construction, automobile plant presses, military vehicles, and even rocket boosters have been loaded onto barges for shipping via the Tennessee River.

 

Blue Ridge Dam rehabilitation project update

TVA’s Blue Ridge Dam Rehabilitation Project is progressing smoothly, says project manager Samantha Godsey. ‘We are on track to begin refilling Blue Ridge Reservoir next spring.”

Godsey says efforts are currently focused on completing construction of the soldier pile wall, which will hold back the soil at the penstock excavation site.SoliderPileWall

"A soldier pile wall is similar to a retaining wall, but much stronger because of the way it is anchored and the fact that the vertical steel beams are installed in a shaft drilled into bedrock and backfilled with concrete.”

Crews also are working on the upstream face of the dam, she says. “We’ve removed the old riprap, and we’ve started re-armoring the bottom third of the dam. The process, which will be repeated for each third, involves grading the soil and placing layers of sand, crushed rock, and new riprap.

In the weeks ahead, workers also will begin putting in the anchors that will stabilize the water intake tower and installing the equipment that will be used to position the new liner inside the penstock.

Recent visitors to Lake Blue Ridge Marina may have noticed another ongoing TVA project, says Godsey.

“We are replacing the perforated hosing suspended above the reservoir bottom on the upstream side of the dam. This hosing is used to bubble gaseous oxygen into the water before it is pulled through the dam, which improves conditions for fish and other aquatic life in the tailwater.”

Read more about the Blue Ridge Dam rehabilitation project and sign up for regular e-mail updates.

 


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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