TVA’s Dams and Reservoirs Help River System Flourish

Darrell Guinn remembers well the heavy rains of February 2019.

Portions of the Valley region received about three times the normal amount of rainfall that month, inundating the Tennessee River system.

Guinn, senior manager of Tennessee Valley Authority’s River Forecast Center, worked around the clock with his team to carefully manage water flows through TVA’s series of dams along the river system.

As the water continued to rise, the phones rang constantly at the River Forecast Center, a 24-hour-a-day, 365-day-a-year operation in Knoxville, Tennessee.   

All hands were on deck. 

Ultimately, Guinn and his team helped soften the blow of the rainfall.  

“Teamwork is essential in the River Forecast Center, especially during a challenging situation or flood event,” Guinn said.

It’s important for each team member to evaluate conditions and make operational decisions related to the part of the system for which they’re responsible, he said.

With each changing weather pattern, it’s all about striking the right balance.

Life-Giving Oxygen 

The Valley region is renowned for beautiful, flowing rivers that provide recreation, rich biodiversity, good standards of living and a plethora of other benefits.  

But the complex river system can sometimes present challenges when it comes to maintaining a healthy water flow.

That’s where TVA’s River Management specialists come in.

They monitor rainfall, river flows, water temperature and dissolved oxygen content to ensure the river system and its dams and reservoirs can enrich aquatic life while also serving as critical resources for power production, navigation and recreation.

Dissolved oxygen is essential to the survival of aquatic wildlife and biomes.

TVA specialists can manage the river’s dissolved oxygen content in a variety of ways, including the use of generators, weirs and other technology. 

Generators, for example, are used intermittently to send water downstream, creating a minimum flow through the rivers system’s dams. This ensures the water has the oxygen it needs to help aquatic habitats flourish.

Physical structures such as weirs are also effective.

“The water cascades over the weir, entrapping air to bring oxygen into the water downstream,” Guinn said.

TVA’s most engineered method of controlling dissolved oxygen content involves converting liquid oxygen into gaseous oxygen. The gas is distributed into the water through a perforated tube anchored to the bottom of a reservoir, creating thousands of tiny bubbles.

The flow carries this oxygen-rich water through the dam during generation and it then moves downstream.

The Right Temperature

Temperature has a significant effect on water quality in the river system.

Nuclear plants and coal plants use water to cool their systems, but when this water is released back into the river it must be kept within certain temperatures. TVA monitors these temperatures in real time to ensure they’re helpful to aquatic habitats.  

“Our policy is designed with all kinds of different environmental factors in place,” James Everett, TVA River Management general manager, said. “As it gets incrementally warmer through the summer, our flows increase to support water quality.”

The River Forecast team will also schedule generation at certain times of day, such as morning, to ensure the cool water from the reservoir reaches downstream locations during the hottest time of the day. This helps protect areas that are sensitive to high water temperatures.

Gauging the Rain

Mention water flow management and most people will think of rainfall.

TVA’s River Management team, well-versed in flood management and drought management, harnesses the power of TVA’s dams and reservoirs to help manage what Mother Nature might have in store for the Valley region.

River flow is adjusted by managing the supply of water held in the reservoirs, which are also important resources for recreation and drinking water.

In seasons of heavy rainfall, the reservoirs have been lowered so they can store excessive runoff from the rainfall to reduce or prevent flooding downstream of the dam. 

When there’s less rainfall, TVA can use the water stored in the reservoirs to maintain adequate river flows, providing navigation, recreation and adequate water supply and water quality throughout the river system. The river flows also protect water quality.

“If you have adequate precipitation, usually concerns are mitigated,” Guinn said. “It is when you have a lack of precipitation that you usually have to make alterations to your operations.”

Amid the changing seasons and weather variability in the Valley region, the reservoirs serve as great equalizers.

“When conditions turn dry, this system of reservoirs help to supplement flow back into rivers and provide great benefit to the Valley,” Everett said.