During torrential storms in the summer of 2018, rain fell so heavily in parts of Wisconsin that earthen and concrete dams built to contain small, prized lakes and reservoirs unleashed torrents of water on farms, roads and bridges. Firefighters rushed to rescue homeowners and their families as three dams breached that June and then as five more followed in advance of Labor Day weekend.
Sherry Hunt, an agricultural engineer and an expert in design of earthen dams at the Department of Agriculture, left her Oklahoma home to trudge through soggy southwest Wisconsin fields following the Labor Day inundation.
The flooded Wisconsin lakes had been formed with man-made dams like those built across the country, and Hunt needed to know how to prevent future dam failures and massive overflows from occurring. It was her job in USDA’s Agricultural Research Service to help find ways to avert further crises and strengthen thousands of dams throughout the country.
By all accounts, she has succeeded.
“Sherry Hunt is an internationally renowned agricultural engineer who has developed much of the design and methodology now used to rehabilitate the sprawling infrastructure of dams across the United States,” said Simon Liu, acting administrator of the Agricultural Research Service. “She is at the source of the science and the data that helps keep our dams safe.”
For example, Hunt developed standardized design criteria for a new kind of concrete spillway that can be constructed over the top of aging or weakened dams when nearby population growth has precluded extensive reconstruction. Her approach involves designing a structure made from a unique mixture of concrete called “roller compacted concrete” that is placed using highway paving equipment.
This makes the dam improvements easier, faster, cheaper and more widely available. When the water comes over the top, it goes down as if walking a staircase, slowing the flow and preventing a massive breach that could devastate communities and farmland located downstream from the dam.
“Her design guidelines and engineering analysis tools have been used all over the United States and internationally to secure the life of aging dams for private, rural, residential and urban land,” said Rep. Frank Lucas, R-Okla., a former House Agriculture Committee chairman.
There are 95,000 dams in the U.S. National Inventory of Dams. USDA’s Natural Resources Conservation Service provided technical and financial assistance to local communities to build approximately 12,000 of them for flood control, and found other beneficial uses like securing water for rural and urban use while creating recreational lakes and conservation areas. Many were built in the 1950s and 1960s, largely in rural areas.
Developers in nearby cities soon realized that the lakes and reservoirs also made the landscape attractive for new suburbs. But scientists discovered that the dams’ sandstone bedrock, soil and vegetation could erode and weaken, putting these growing populations at risk. Predictions of increased severe storms due to climate change made Hunt’s challenge even more urgent.
Her trip after the Wisconsin floods illustrates how she goes about the work. She and a local team took photos and gathered soil samples, noting where the erosion had begun. They examined where trees and fence posts abutted the land. They looked for tire tracks and cattle trails on and near the dams and spillways, as these can trigger erosion if water flows over the dam during large storms like ones that had just occurred.
Hunt found that the natural materials in the abutments adjacent to the dam were fractured rock that allowed water to seep through the cracks for many years. This appeared to create a weak point, she said.
Using this data, Hunt’s team ran computer simulations to not only help identify the causes of the failure of five dams, but also to provide further model validation. The insights will drive research to improve predictions, anticipate failures and aid dam design and construction.
Had her resulting design methods been available when the dams were built, “many dam failures or near failures could have been avoided,” Hunt said.
“There are just not that many people in America who have the role of actually doing cutting-edge research on how to improve dam building,” said Lori Spragens, executive director of the Association of State Dam Safety Officials. “She is shaping our understanding of how to rehabilitate dams in this day and age.”
Larry Caldwell, a retired national dam rehabilitation coordinator at USDA, said Hunt’s cutting-edge design research has resulted in criteria that is “now used all over the country and shared around the world.”
“Without Sherry Hunt’s work, dam structures would be less safe,” Caldwell said. “She is an evangelist for dam safety and research.”