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March 14, 2011

In this issue:

Rain and runoff
Current Reservoir Conditions
Historical reservoir elevations
Reservoir Operations
Questions and answers about the spring fill
Special Reservoir Operations
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

Rainfall & Runoff Chart 1887-2007
Valley Rainfall
The heavy rains early in March are a reminder that the Tennessee River watershed has one of the highest annual rainfall totals of any watershed in the United States, with an average of 51 inches of rain a year. The Gulf of Mexico, located to the south, provides a major source of moisture. Wintertime storms provide the most rainfall because they generally cover a larger area and are greater in duration and frequency. The basin also is subject to heavy rainfall resulting from dissipating hurricanes moving across the southeastern U.S. in late summer and early fall

In over 100 years of record-keeping, the annual rainfall has varied between a high of 65 inches in 1973 and a low of 30.65 inches in 2007. The greatest extremes occur in the eastern half of the Tennessee Valley region. The average annual precipitation at several locations in the mountains of the French Broad, Hiwassee and Little Tennessee River watersheds exceeds 80 inches. In contrast, other locations in the French Broad and Holston River watersheds have annual averages of less than 40 inches.

Average monthly rainfall/runoff comparison
The monthly average rainfall in the Tennessee Valley region ranges from 3.0 to 5.5 inches. March, July and December are typically the wettest months, and September through November are typically the driest. Of course, in any year the wettest and driest months may be different.

The average annual runoff in the region — the amount of water that ends up in the reservoirs and river system after it rains — is about 23 inches, or 44 percent of the average annual rainfall over the watershed. The monthly average runoff varies from a high of almost four inches in March to a low of less than one inch in August, September and October. Generally, runoff is heaviest in the winter and early spring, when the vegetation is dormant and the ground is saturated. As a result, heavy storms moving across the Tennessee Valley region between December and early May become potential causes of major floods.

Current reservoir conditions

All main-river reservoirs are currently spilling to recover flood-storage capability. Tributary reservoirs are above seasonal elevations as shown in the chart below.

Tributary Reservoir Elevations¹
Reservoir

March 13, 2011
Observed Elevation

March 1
Flood Guide

Feb. 1
Flood Guide

South Holston

1720.9

1710.3

1729

Watauga

1956.6

1952

1959

Cherokee

1055.3

1045

1070.9

Douglas

974.8

954

994

Fontana

1667.6

1653

1703

Norris

1013.5

1000

1020

Chatuge

1920.3

1918

1926

Nottely

1772.6

1762

1777

Hiwassee

1496.8

1485

1521

** Blue Ridge

1625.9

1672.3

1687

Tims Ford

884.2

877.8

888

Normandy

868.44

864

875

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 Dam Rehabilitation
TVA is rehabilitating Blue Ridge Dam in Northern Georgia. The project includes repairs to the penstock (the underwater pipe that carries water from the reservoir to the turbines in the powerhouse) and work to stabilize the water intake tower and upstream and downstream faces of the dam. TVA began slowly lowering the elevation of the Blue Ridge Reservoir in mid-July 2010 with the objective of reaching an elevation between 1620 and 1630 feet above sea level by mid-to-late October. Barring construction delays due to heavy rains, the reservoir should begin refilling next month depending on rain fall and runoff.

Historical reservoir elevations
Ever wondered what’s the highest your reservoir has been – or the lowest? The table below shows the maximum and minimum elevations since initial filling of the reservoirs.  Keep in mind, though, that TVA operated the Tennessee River system differently when all but one of the minimum reservoir elevations shown occurred. TVA’s current operating policy targets higher winter elevations on most of the tributary reservoir system, which makes it unlikely—barring an extreme drought or a deep drawdown for maintenance—that the minimum levels shown below will occur in the future.


Reservoir

Maximum Elevation

Date

Minimum Elevation

Date

Apalachia

1281.40

6/13/1953

1251.00

4/25/1971

Bear Creek

609.43

3/17/1973

547.00*

9/27/1976

Blue Ridge

1691.54

2/11/1946

1587.75

1/16/1956

Boone

1384.99

5/19/1964

1327.06

1/23/1956

Cedar Creek

587.43

5/8/1984

559.48

12/5/1980

Chatuge

1928.39

5/28/1973

1860.11

9/5/1947

Cherokee

1074.48

6/19/1989

980.77

1/7/1954

Chickamauga

687.13

5/7/2003

673.27

1/21/1942

Douglas

1002.45

5/9/1984

883.70

1/16/1956

Fontana

1710.20

5/28/1973

1472.00

1/29/1955

Ft. Loudoun

816.07

3/28/1994

805.54

1/18/1954

Ft. Patrick Henry

1263.80

2/11/1954

1223.86

12/4/2002

Great Falls

811.26

12/23/1990

761.98

1/10/1940

Guntersville

596.29

3/2/1944

590.65

11/12/1968

Hiwassee

1528.02

5/28/1973

1413.41

1/28/1948

Kentucky

369.99

5/11/1984

348.02

3/11/1961

Little Bear Creek

625.38

5/8/1984

599.30*

12/5/1977

Melton Hill

796.45

3/16/1973

784.10

2/9/1966

Nickajack

634.99

4/19/1969

630.82

2/20/1968

Normandy

880.12

2/20/1991

852.10

1/31/2008

Norris

1031.10

2/11/1937

909.35

1/24/1956

Nottely

1781.47

5/28/1973

1638.60

10/6/1947

Ocoee No. 1

835.20

2/16/1990

808.10

1/11/1940

Ocoee No. 3

1437.40*

4/28/1958

1381.00

10/18/1978

Pickwick

419.49

3/30/1944

407.12

12/18/1944

South Holston

1736.92

4/27/1987

1614.15

1/13/1956

Tellico

816.20

3/28/1994

806.96

1/14/1980

Tims Ford

894.55

12/10/2004

855.25

12/1/1997

Upper Bear Creek

802.73

12/23/1990

790.13

10/31/1982

Watauga

1963.34

9/19/2004

1813.47

1/13/1956

Watts Bar

747.35

5/7/2003

733.44

3/20/1945

Wheeler

557.32

3/1/1944

548.43

12/9/1962

Wilson

508.38

5/19/1983

502.98

7/9/1942


*Estimated

 

Reservoir Operations

Water spills at Guntersville Dam in northeastern Alabama at more than 152,000 cubic feet per second (more than 1.1 million gallons per second). This photo is from Thursday, March 10.Water spills at Guntersville Dam in northeastern Alabama at more than 152,000 cubic feet per second (more than 1.1 million gallons per second). This photo is from Thursday, March 10.
TVA’s River Forecast Center has been especially busy managing the river and tributaries after heavy rains throughout the TVA service area in early March.
“We are monitoring weather conditions and working with the River Operations team and other organizations to minimize potential flooding and ensure continued navigation,” TVA River Forecast Center Manager David Bowling says.

Some areas in the Tennessee Valley have seen more than 6 inches of rain since March 5. Bowling’s team is focused on recovering flood-storage capability in the main river reservoirs. To do so, the center is storing tributary reservoir water and spilling at the main river dams so high flows can recede.

Other agencies are coordinating with TVA. TVA’s River Forecast Center works closely with the U.S. Army Corps of Engineers on Kentucky Reservoir to minimize flooding below Pickwick. Minimal flooding below Pickwick reduces the threat to spring crops and other agricultural interests in lowlands near Savannah, Tenn. The center is also partnering with the U.S. Coast Guard to reduce impacts to navigation and in close contact with the National Weather Service. NWS helps to disseminated river conditions to the public.

There is no significant rain in the extended forecast at this time. Bowling says spilling at the dams will continue until ensure reservoir levels are within seasonal ranges.

To learn more about what the River Forecast Center does to manage the Tennessee River system, go to http://www.tva.gov/river/flood/center.htm.

 

Questions and answers about the spring fill

When will the water level in my reservoir start going up?
TVA begins aggressively storing water to fill tributary reservoirs in mid-March. This is because less flood storage space is needed in the spring when the roots of growing plants begin to intercept more of the rain that would otherwise run off into the reservoir system. In addition, weather patterns begin to change with less chance for larger, more organized storm systems.

Main-river reservoirs are kept at lower levels until mid-April or May because they have limited flood storage space compared to tributary reservoirs due to topography and the requirement in the TVA Act to provide a nine-foot waterway for commercial navigation on the main Tennessee River. However, since there is not as much difference between winter and summer levels on main-river reservoirs as on tributary reservoirs, it doesn’t take long to bring main-river reservoirs to summer elevations.

When will my reservoir reach “full pool”?
TVA tries to fill tributary reservoirs to summer levels by Memorial Day weekend. Most main-river reservoirs are targeted to fill by mid-April. Watts Bar, Chickamauga, and Fort Loudoun Reservoirs are targeted to fill by mid-May to help reduce the risk of flooding at Chattanooga, Tennessee.

When reservoirs actually reach targeted levels depends on rain and runoff. Beginning in mid-March, tributary reservoirs are allowed to fill as quickly as possible, as long as reservoir levels do not significantly exceed flood guide elevations (which allow for higher reservoir levels in the spring). If low rainfall prevents reservoirs from filling at the desired rate, TVA stores as much water as possible, allowing only minimum releases to meet downstream flow requirements.

What is full pool on my reservoir?
To see the targeted summer pool levels for TVA-managed reservoirs, go to TVA’s Reservoir Information web page. Choose your reservoir from the pull-down menu and then select Operating Guide.

For main-river reservoirs, you'll see a gray band showing the normal operating zone, which is highest during the summer months. For tributary reservoirs, you'll see a blue line representing the flood guide elevation, which is at the highest level on June 1. This line is set to support reservoir recreation from June 1 through Labor Day, while still preserving a small amount of flood storage capacity as a protection against a potential flood-producing summer storm.

Why isn’t my reservoir filling as fast as other reservoirs?
If your reservoir doesn’t seem to be filling as fast as a neighboring reservoir, it could be because your area isn’t getting as much rain. Rain amounts often vary widely even over adjacent watersheds, with direct impacts on the rate that reservoirs in each watershed fill.

Fill rates also can vary significantly from one reservoir to another due to differences in the size of the land area draining into each reservoir, the amount of ground cover, soil characteristics, and reservoir shape and surface area.

 

Special reservoir operations

Blue Ridge
Blue Ridge Rehabilitation Project
– TVA is continuing its work to replace the penstock (the pipe that carries water from the reservoir to the powerhouse to generate electricity). Currently, TVA is installing sections of the new penstock (picture to the right). On April 1, TVA is scheduled to have the reservoir elevation at 1,630 feet and will allow it to fill from there.

Ocoee Flume Repairs – You may have seen reports on the Ocoee Flume repairs in last few weeks in the newspaper or on TV. Since April 2010, TVA has worked daily to return this piece of history to operation following a rockslide. With a focus on safety, the project is near completion. TVA expects to be making electricity at its Ocoee #2 powerhouse later this spring.

 


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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