The University of Alabama and the Tennessee Valley Authority (TVA) are undertaking a project to dig up the flood history in the Tennessee River Valley.
Associate Professor of the Department of Geography at the University of Alabama, Dr. Lisa Davis was recently on assignment with Ph.D. student Rachel Lombardi to find out more information about flooding in the Tennessee Valley. In an area about one mile from the river in Marshall County, the team was looking for clues in sediment to tell whether floodwaters once covered the area.
Davis called them paleofloods. These are floods in the past that can be discerned from the sediment deposits that are left behind.
“We’re interested in floods that happened as far back as 10,000 years ago, particularly the largest ones,” she said.
According to Davis, there is a record of about 150 years, but extreme flooding can go hundreds, if not thousands, of years between occurrences.
The goal of the project was to work with TVA engineers. They wanted to integrate paleoflood data into flood frequency and dam safety assessments to help these assessments better account for the most extreme floods. They are building on thousands of years of paleoflood data available from an earlier collaborative research by collecting paleoflood data from sheltered caves located in bluffs high above the Tennessee River.
The team was looking for mica. Mica is a mineral that comes from the Great Smoky Mountains. If there is evidence of it in this location, there is a possibility of paleoflood activity. At the test site, Lombardi did not find any indication of mica which may mean that the floodwaters did not reach this area. They will have to have other lab tests to confirm this. The reason they are looking for mica is to see if there is evidence of the area flooding.
Lombardi and Davis examined the dirt. Lombardi explained that through touch she was able to determine some of the material in the soil. She said, for instance, she was feeling of the top soil and felt sand. In one layer she felt pebbles and explained they felt round.
She did a test using the color of the dirt, both wet and dry. The soil was different once it was wet. She said that the wet test could show more results.
Davis examined the dirt under a microscope. In the second layer, the texture looked like a peanut butter cookie mix.
“We have to know more about the worst floods to be able to accurately assess the severity of a recent one, “Lombardi said. “How can we say it’s the worst flood in 500 years if we don’t have flood information going back 500 years? For this reason, paleoflood records, combined with instrument and historical observations, provide the most robust context for assessing floods.”
TVA lead hydrologist Curt Jawdy said they are learning every day, but it important to continue to do research. With February 2019 being the wettest month in recent history, TVA’s 49 dams stored at least 3.5 trillion gallons of water. This reduced the downstream impact to the hardest-hit areas in west Tennessee and parts of northern Alabama. In these places, the areas saw as much as 13.5 inches of rainfall in a two-week time period.
With a partnership between the University of Alabama and TVA, people in and around the Tennessee River can see the impact a flood had in their area along with being prepared for possible future events of flooding.
After the team finished at the location in Marshall County, they were going to examine some caves. These caves would tell if flooding was or could still be an issue.