(Photo: Iowa Soybean Association / Alex Schaffer)
What you should know before restoring an oxbow
May 31, 2024 | Brandon Iddings
Looking across Iowa, you see rolling hills of soybeans and corn bisected by small, meandering prairie streams. Along these streams, we have old river scars, where, before settlers, herds of bison wandered the prairie that we now call home. Today, these old scars, called oxbows, are slowly losing their functions due to sedimentation from increased erosion or man-made stream straightening. Iowa Soybean Association (ISA) has been involved in restoring these oxbows since 2011.
What is an oxbow?
An oxbow is an old meander of the stream that gets cut off from the main channel during the natural river cycle. Over time, these scars fill in with sediment and lose their hydraulic abilities, reducing habitat value, water quality benefits, and/or flood storage. In some cases, these benefits are lost completely.
ISA’s goal with our partners is to help farmers and landowners restore these areas and return their benefits to people and wildlife. These restorations are relatively simple and are usually in unproductive or unprofitable areas. One contractor put oxbow restoration this way: “You take a big yellow machine and dig a hole.” While that is true to a certain extent, there are other important factors to consider during a restoration project.
A successful project includes restoring the oxbow to its natural state after disconnection from the mainstream or river. We get to that natural state by digging down to the historic stream bed. Usually, this is 4-6 feet below the sediment that has filled these areas. Once you reach the post-settlement alluvium depth, water percolates into the oxbow, which connects to the water table. The sedimentation taken from these oxbows is usually fertile, black soil that can be returned to the crop fields from where it came. One farmer commented that just one year after the project, he saw a 10-20 bushel increase in the areas ISA and partners put the reclaimed soil.
Water quality benefits
Oxbows have been shown to treat an average of 62% of nitrates from tile-fed multipurpose oxbows, according to Journal of the American Water Resources Association. With access to the oxbows set at a minimum of 3:1 slope, these areas are compatible with cattle. Cattle use these pools to cool down or get water, similar to the buffalo who once used them to cool down or wallow in. On average, oxbows hold a million gallons of water in a one-acre pool. Some cities are restoring oxbows to help with flood mitigation during high flows. Around these restorations, we also try to restore another diminishing habitat, pollinator prairies. These pollinator plantings provide a stacked benefit to the oxbows by creating additional habitat and helping slow future erosion into the oxbows with their deep roots.
Habitat for the Topeka shiner
Oxbows provide critical habitat to the Topeka shiner, one of Iowa’s endangered species. These restorations act as nurseries for the fish when the river floods. According to the United States Fish and Wildlife Service USFWS) Species Status Assessment, Iowa’s primary conservation action regarding recovery of the Topeka shiner is habitat via oxbow restoration.
ISA has successfully completed dozens of restoration projects on private lands in collaboration with The Nature Conservancy (TNC), USFWS, Syngenta and other partners. These projects have greatly benefited the species in the past 20 years, with half of restored oxbows now having Topeka shiner populations. Moreover, the Topeka shiner has been discovered in White Fox Creek in Iowa for the first time in more than 36 years.
Like the recovery of the American bison, farmers and landowners are showcasing voluntary conservation actions in their working lands to recover another species. These restorations in Iowa are one of the reasons that the USFWS in 2023 recommended the species be downlisted from endangered to threatened. This is a huge step in showcasing how the focus work of partners, agencies, landowners and others can achieve outcomes critical to species recovery.
ISA is steadily working to grow conservation and habitat efforts to create offsets that show that volunteer conservation is effective.
ISA is driven to deliver constant growth in production and profitability now and into the future as we identify challenges and create innovative sustainable solutions to enable farming for future generations. Even though we no longer have buffalo herds wandering our state, these oxbows can still provide considerable benefits to farmers, landowners, water, fish and other wildlife, just like they did all those years ago.
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