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June 2, 2010

In this issue:
Rain and runoff
Reservoir elevations
Reservoir operations
In answer to your question about the May 1-2 flood
Blue Ridge drawdown to begin in mid-July
Safe boating in barge traffic
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

After three months of below-normal rainfall, the eastern Tennessee Valley received some much needed rain in May, as the chart below shows.

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

Eastern Valley rainfall for the year to date is 78 percent of normal.

Runoff (the amount of water that reaches the river system when it rains instead of being absorbed into the ground) is currently 94 percent of normal in the eastern Valley.

 

Reservoir elevations

The eastern Valley received just enough rain in May to fill most tributary reservoirs to June 1 target elevations on schedule. The only exceptions were South Holston and Cherokee Reservoirs. South Holston was within a foot of its target level on June 1 and should fill later this month. Cherokee, on the other hand, was seven feet below its June 1 target level.  TVA will continue to restrict releases from Cherokee to minimum flows to bring the water level up, but it will take above-normal rainfall in the area draining into Cherokee to bring the reservoir to summer levels.

Tributary reservoir elevations¹

Reservoir

June 1, 2010
Observed Elevation

June 1
Flood Guide Elevation2

South Holston

1728.2

1729

Watauga

1958.7

1959

Cherokee

1064.1

1071

Douglas

994.2

994

Fontana

1703.9

1703

Norris

1020.3

1020

Chatuge

1926.1

1926

Nottely

1777.2

1777

Hiwassee

1521.4

1521

Blue Ridge

1687.4

1687

Tims Ford

888.3

888

Normandy

875.1

875

¹Elevations above mean sea level
²Flood guide elevations show the amount of storage allocated for flood damage reduction during different times of the year. From June 1 through Labor Day, TVA's goal is to meet downstream flow requirements while keeping the reservoir elevation at the dam as close to the flood guide level as possible to support reservoir recreation. During this period, reservoir elevations fall below the flood guide only when rainfall and runoff are insufficient to meet flow requirements. The rest of the year, the primary objective is to keep the reservoir elevations at or below the flood guide to ensure there is enough space in the reservoir to store the rain and runoff from flood events.

 

Reservoir operations

Beginning June 1, TVA restricts the drawdown of tributary storage reservoirs to enhance recreation opportunities.

The goal is to keep tributary reservoirs as close to their flood guide levels as possible, explains Chuck Bach, TVA General Manager for River Scheduling.

“Flood guide levels are always an upper bound. The only time we allow a reservoir to go above its flood guide level is during a flood event, and then we lower the water level as soon as the downstream floodwaters begin to recede to recover flood storage space for future storms.

“But in June, July, and August, flood guide levels are also target levels. In summer, we restrict releases with the objective of keeping tributary reservoir elevations as close as possible to their flood guide levels. The rest of the year, tributary reservoir levels may fall below flood guide levels by several feet to satisfy other operating objectives.”

Releases are restricted during the summer, not eliminated, emphasizes Bach.

“Under normal operations, we restrict releases to minimum flows from June 1 through Labor Day. We release just enough water to meet reservoir-specific and system minimum flow requirements.”

Reservoir-specific minimum flow requirements protect downstream aquatic habitat and serve a variety of other purposes such as waste assimilation and water supply.  They vary from dam to dam depending on reservoir size, turbine generating capacity, the water needs of downstream industries, and other factors. System minimum flow requirements, measured at Chickamauga, Pickwick, and Kentucky dams, ensure an adequate flow of water throughout the river system.

The Chickamauga system minimum flow requirement ensures adequate flows throughout the tributary reservoir system and the upper Tennessee River system. In dry years, it can have a significant impact on tributary reservoir levels, says Bach.

“If there isn’t much rain, the only way we can meet the Chickamauga flow requirement is by releasing some of the water stored in tributary reservoirs—and that means lower water levels for those reservoirs. In that case, we follow reservoir balancing guidelines to make sure that water is drawn from upstream reservoirs equitably.”

Balancing guides define the bottom of the normal operating zone for individual tributary reservoirs. They are used in conjunction with flood guides, which define the top of the operating zone. When extra water is needed to meet downstream flow requirements, TVA looks at the elevation of each reservoir is relation to these two guides and then decides how much water to withdraw from specific reservoirs in order to bring reservoir elevations into balance—i.e., to keep the elevation of each reservoir similar relative to its position between the flood guide and the balancing guide.

The river flow at Chickamauga Dam cannot be lower than the amount specified in the table below to ensure an adequate flow of water through the system, and it cannot be higher in order to conserve as much water as possible in tributary reservoirs—except in a flood situation when higher releases are necessary to recover flood storage space.

Chickamauga System Minimum Flow Requirements, June 1 - Labor Day

 

Weekly average minimum flow at Chickamauga Dam
(cubic feet per second)

June 1 - July 31

August 1 - Labor Day

If the volume of water stored in tributary reservoirs is below the system minimum operating guide

13,000 cfs

25,000 cfs

If the volume of water stored in tributary reservoirs is above the system minimum operating guide

Increases from 14,000 cfs
the first week of June
to 25,000 cfs
the last week of July

29,000 cfs

The Chickamauga system minimum flow requirement depends on the total volume of water stored in the 10 largest tributary reservoirs. It is lower if there is limited water in storage and higher if there is ample water in storage.

The Chickamauga system minimum flow requirement increases in August because warmer air temperatures result in warmer river temperatures, which means more flow is required to protect aquatic habitat and water quality.  The higher August flow requirement also helps to control power rates by allowing TVA to generate more hydroelectric power to meet the high power demand which typically occurs in late summer due to the higher temperatures.

Go to Managing River System Flows for current information about the volume of water stored in tributary reservoirs and observed average weekly flows at Chickamauga Dam.

 

In answer to your question about the May 1-2 flood

Why didn't TVA stop the flooding in Nashville?
That’s what some Middle Tennessee residents asked after the May 1-2 flood event.

First, TVA does not manage the Cumberland River. It’s managed by the U.S. Army Corps of Engineers. But the reality is that any river flood-control system would have been seriously challenged by the record-setting rains from the storm system that moved over western and middle Tennessee in early May.

Rainfall amounts ranged from 12 to 15 inches north of Memphis over to Nashville, and Doppler radar estimated that as much as 23.8 inches fell in the Columbia, Tennessee, area south of Nashville.

TVA began coordinating management of the Tennessee River system with the U.S. Army Corps of Engineers as that agency worked to manage the Cumberland River and mitigate damage.

In the Nashville area, extensive flooding occurred along the Cumberland River, and TVA supported the Corps of Engineers by coordinating release of water from Kentucky Dam into the Ohio River near where the Cumberland flows into the Ohio. The Corps controls eight dams on the Cumberland River.

Chuck Bach, general manager of River Scheduling, said Kentucky Reservoir reached a near-record water elevation of 369.7 feet above sea level on Saturday, May 8. The record high of 369.9 was reached in May 1984.

TVA also closely monitored and responded to high water levels on the Tennessee River, according to Bach.

“Pickwick Reservoir was at the top of its operating range because we’d been limiting generation to conserve water due to the dry conditions.  Consequently, we were able to increase power generation at Pickwick Dam in advance of the storm. That allowed us to lower the reservoir level by about a foot and gave us more room to store the predicted rain. While the heaviest rain was falling on the western part of the region, we held the flow of water through the tributary dams in the east to minimum flows, and that helped reduce flows on the Tennessee River. Then, after the rain let up, we allowed the reservoirs on the main river between Knoxville and Chattanooga—Fort Loudoun, Watts Bar, and Chickamauga—to rise to summer levels or slightly higher to continue managing the high water levels in the western Valley.”

Although the bulk of the flooding occurred in the Middle Tennessee area from the Cumberland and local streams, North Alabama also experienced flooding in the Shoal Creek area above Wilson Dam where about 160 small boats broke loose from their docks at a marina. TVA Police helped local officials secure the loose boats.

River Operations drew Wilson Reservoir down to its low summer range to hold additional water as the storm moved across the area from the west.

The storm system also spawned tornadoes and high winds that caused power interruptions on the TVA system, in addition to local utility outages caused by the flooding and storms.

 

Blue Ridge drawdown to begin in mid-July

TVA will begin lowering the level of Blue Ridge Reservoir in Fannin County, Georgia in mid-July in order to rehabilitate the dam.

The drawdown will occur gradually over a 16-week period with the goal of lowering the reservoir to an elevation of 1,630 feet above sea level (57 feet lower than the usual summer elevation) by November. The reservoir will be kept at an elevation between 1,620 and 1,630 feet above sea level until planned repairs to the penstock (the underwater pipe that carries water from the reservoir to the turbines in the powerhouse) can be completed.

Blue Ridge Drawdown

TVA expects to complete the repairs in time to begin refilling the reservoir in April, although unexpected events such as sustained heavy rains could prolong the drawdown.

According to TVA project manager Samantha Godsey, beginning the drawdown in mid-July minimizes the chance that rainfall will interfere with the construction schedule and maximizes the chance of reaching normal summer pool elevations in time for the 2011 recreation season.

“The choice is between impacting part of the 2010 recreation season and increasing the risk of completely eliminating the 2011 season if the weather delays the scheduled work.”

TVA is installing a new liner in the penstock, which was damaged due to excessive water pressure the first time it was filled with water in 1931. TVA, which acquired the dam from Tennessee Electric Power Company in 1939, has periodically lowered the water elevation for dam safety inspections due to the deteriorating condition of the penstock.

The penstock repairs will begin during the regularly scheduled deep drawdown for the 2010 dam safety inspection and should eliminate the need for regularly scheduled deep drawdowns in the future.

TVA also will reinforce the intake tower and stabilize the upstream and downstream sides of the earthen dam as part of the project.

TVA will work with the Fisheries Management section of the Georgia Department of Natural Resources to reduce adverse temperature impacts on the trout fishery below the dam and will continue to provide water releases for Ocoee River rafting to the extent practical given the weather.

Check the Blue Ridge Dam Rehabilitation Project Web page for project updates.

 

Safe boating in barge traffic

Boaters on the Tennessee River need to exercise extreme caution when operating near commercial barge traffic.

A fully loaded 15-barge tow can carry the same weight as 900 tractor-trailers and are very difficult to maneuver. For this reason, commercial tows have the right-of-way in the main channel of the river. It is important to give them lots of room since they cannot get out of the channel to steer around you and may need up to one and a half miles to stop. A person falling from a personal watercraft about 1,000 feet in front of a moving tow has less than a minute to get out of the way.
Follow these rules when boating in barge traffic:

barge
  • Don't anchor in the river channel, and never tie off to a navigation buoy.
  • Beware of the blind spot that can extend for several hundred feet in front of and to the sides of barges.
  • Avoid the turbulent waters created behind a towboat by the propellers.
  • When you cross the main channel of the river, always proceed in high-visibility areas.
  • Take extra care when boating at night. The navigation lights on the front and rear of a tow can be as much as a quarter-mile apart.
  • Know the danger signal. Five or more short whistle blasts indicate immediate danger. Make sure they are not directed at you.
  • Avoid excessive speed.

Excerpted from “Tennessee and Cumberland Rivers: A boater’s guide to safe travel,” produced by the U. S. Army Corps of Engineers, Nashville District, and TVA.    

Delta MarinerAt left: The Delta Mariner, squeezing through the 110-foot by 600-foot Wheeler Lock. Wheeler is the first of four Tennessee River navigation locks the Mariner will transit as it carries rocket components manufactured in Alabama to launch sites in Florida and California. Built to safely transport high value cargo that is too large to efficiently travel by highway or rail, the 85-foot by 312-foot, 8,000-horsepower Mariner is the largest vessel to operate on the nation's Inland Waterway System.

 


Get more information on TVA.com

TVA’s public website has been redesigned to make it easier for visitors to navigate and find the information they want. The new look incorporates striking photography, along with user-friendly navigation elements. Check it out at www.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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