Managing River System Flows

In May 2004, the TVA Board of Directors approved a new policy for operating the Tennessee River and reservoir system. This policy shifts the focus of TVA reservoir operations from achieving specific summer pool elevations on TVA-managed reservoirs to managing the flow of water through the river system.

The new policy specifies flow requirements for individual reservoirs and for the system as a whole. Reservoir-specific flow requirements keep the riverbed below that reservoir’s dam from drying out. System-wide flow requirements ensure that enough water flows through the river system to meet downstream needs.

These flow requirements help to enhance recreation opportunities on tributary storage reservoirs while meeting other needs: protecting water quality and aquatic resources, ensuring year-round navigation and providing water for power production and municipal and industrial use.

TVA enhances recreational opportunities by restricting the drawdown of tributary storage reservoirs during the summer — from June 1 through Labor Day. During this period, under normal operations, just enough water is released from these reservoirs to meet downstream flow requirements. TVA works to keep the water levels in these reservoirs as close as possible to each reservoir’s “flood guide level” — a guideline that reflects how much storage space each reservoir needs to hold back potential flood waters.

When water must be released to meet downstream flow requirements, a fair share of water is drawn from each reservoir.

System-wide flows are measured at Chickamauga Dam, located near Chattanooga, Tenn., because this location provides the best indication of the flow for the upper half of the Tennessee River system.

If the total volume of water flowing into Chickamauga Reservoir is less than needed to meet system-wide flow requirements, additional water must be released from upstream reservoirs to augment the natural inflows (a function of rainfall and runoff), resulting in some drawdown of these projects. How much water is released depends on the time period and the total volume of water in storage in 10 tributary reservoirs:  Blue Ridge, Chatuge, Cherokee, Douglas, Fontana, Nottely, Hiwassee, Norris, South Holston and Watauga.

Based on the amount of water stored in these reservoirs in relation to the Minimum Operations Guide shown on the graph above, TVA will release enough water to provide the weekly average minimum flows at Chickamauga Dam shown in the chart below.

When dry conditions prevail on the Tennessee River below Chickamauga, it may be necessary to release additional water to meet minimum flow requirements at Kentucky Dam.

System Flow Requirements (June 1 – Labor Day)

	Weekly average minimum flow at Chickamauga Dam (cubic feet per second)
	June 1 - July 31	Aug. 1 - Labor Day
If the volume of water stored in tributary reservoirs is BELOW the Minimum Operations Guide	13,000 CFS	25,000 CFS
If the volume of water stored in tributary reservoirs is ABOVE the Minimum Operations Guide	Increases from 14,000 CFS the first week of June to 25,000 CFS the last week in July	29,000 CFS

 

	Bi-Weekly average minimum flow at Kentucky Dam (cubic feet per second)
	June 1 - July 31	Aug. 1 - Labor Day
Kentucky flow requirement can drive minimum flows when conditions are dry below Chickamauga Dam.	18,000 CFS* at Kentucky Dam	18,000 CFS* at Kentucky Dam

*May increase up to 25,000 CFS for navigation.

Maintaining flood storage space

Water also may be released from tributary reservoirs from June 1 through Labor Day after significant storm events, but only as long as necessary to recover allocated flood storage space.

See for yourself

Check the end point for the Actual Storage line in the Tributary System Operating Guide Graph and determine whether or not it is above or below the Minimum Operations Guide for today's date. Then check the System Flow Requirements chart to see the weekly average minimum flow requirement at Chickamauga Dam and compare it with the actual average weekly flows at Chickamauga Dam shown in the chart below.