Streambank stabilization offers water quality & other benefits for western Iowa's rivers

Water quality is a salient topic across Iowa today. While significant discussion focuses (rightly so) on things like pesticide and fertilizer runoff, one lesser-acknowledged cause of impaired waters is soil erosion, particularly streambanks and stream beds. Soil erosion from fields, including sheet, rill, and gully erosion, also brings sediment into waterways.

Nitrogen and phosphorus are the two main nutrients applied to crop fields and lawns. While crucial for plant growth, too much can impair our waterways and drinking water sources. Generally, nitrogen readily washes off from topsoil with rain and snowmelt, while phosphorous adheres to soil particles and can stay embedded for many years. When a streambank erodes into a waterway, it brings phosphorous with it. Streambank erosion is a leading cause of phosphorous pollution in Iowa’s rivers. Golden Hills is working with NRCS to stabilize streambanks as part of our Regional Conservation Partnership Program. 

Erosion is a natural process of rivers often resulting in meandering where the channel moves back and forth laterally across its floodplain. However, human activities, such as channelization and urbanization, can greatly exacerbate erosion, potentially throwing the entire system out of balance.

Most of western Iowa’s streams meandered across the prairies, replete with wetlands and oxbows in the floodplains, until they were channelized (straightened) in the 20th Century. Channelization reduced flooding and improved drainage for agricultural development, but caused downcutting and widening of our streams & rivers.

Most of the photos and information below is from “Stream Restoration Overview” PowerPoint and “HCA-Geomorph History PowerPoint” from John Thomas, Hungry Canyons Alliance.

Waterways are constantly attempting to reach an energy equilibrium where sediment erosion and deposition are balanced. Since energy cannot be created or destroyed, it must move throughout the river system. 

As a stream picks up more sediment, whether from surrounding uplands or streambanks, friction increases, which reduces the amount of energy expended. In addition to sediment, the channel itself creates friction with the flowing water. Heavier bits of sediment are dropped to the bottom, which further increases energy. The total amount of energy in a waterway also depends on the depth and volume.

When a meandering stream is straightened, its total length decreases over the same amount of elevation change; in other words, the channel becomes steeper, causing it to flow faster. To try and reduce the amount of excess energy, the stream incises (cuts downward) into its streambed. In western Iowa, the highly-erodible deep loess soils were relatively easy to downcut into, resulting in deeply-incised streams and gullies. Channels then widen because the vertical silt banks are easily undercut by flowing water. Streambed degradation can also release legacy nitrates into the water.

Waterways are constantly attempting to reach an energy equilibrium where sediment erosion and deposition are balanced. Since energy cannot be created or destroyed, it must move throughout the river system. Streams regulate the energy at their disposal by carrying different sizes and amounts of sediment, the slope of the streambed, and channel form (or the shape and pattern of the channel).  For example, as a stream picks up or carries more sediment, whether from surrounding uplands, streambanks, or the channel bed, friction increases which reduces the amount of energy available; like putting the brakes on in a car.

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In general, the upper reach of a watershed is erosion-dominant; the middle part of the watershed is transport-dominant, and the lower portion is deposition-dominant. Meanders gradually move down-valley as outer banks erode and inner banks deposit. Large rivers in western Iowa, like the Missouri, Nishnabotna, and Nodaway Rivers, are transport-dominant. Localized instability (i.e., eroding streambanks) are not always a symptom of system instability.

While planting riparian buffers of prairie grasses and trees provide water quality benefits and may help slow the rate of erosion, buffers in western Iowa do not typically stop streambank erosion because the channel bed and banks are adjusting faster than vegetation can take hold and often at a depth deeper than the vegetations roots.
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Meanders gradually move down-valley as outer banks erode and inner banks deposit. Large rivers in western Iowa, like the Missouri, Nishnabotna, and Nodaway Rivers, are transport-dominant. Localized instability (i.e., eroding streambanks) are not always a symptom of system instability. The definition of stability depends on perspective and time.

Looking at the West Nishnabotna as an example, upstream areas like Shelby County are generally experiencing more streambank erosion than downstream areas like Fremont County, where the Nish has many feet of sedimentation in the bed, which contributes to flooding issues in the Riverton and Hamburg areas.

While planting riparian buffers of prairie grasses and trees provide water quality benefits and may help slow the rate of erosion, these buffers typically will not actually stop streambank erosion, as it is a geological process deeper than vegetative roots.

Streambank stabilization has been used successfully on many of western Iowa’s rivers. Increased use of the practice has the potential to significantly improve our water quality.

Benefits of streambank stabilization include: 
•Protecting infrastructure on or near floodplain
•Protecting land on or near floodplain
•Reducing flooding
•Improving water quality
•Creating and reconnecting aquatic and riparian habitats
•Enhancing nutrient processing
•Improving aesthetics and recreational opportunities
•Increased economic development opportunities.
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If you have riverbank property in the West Nish watershed that could use bank stabilization, visit our RCPP webpage to see if you are eligible for cost-share: goldenhillsrcd.org/rcpp

example of a streambank stabilization in progress on the West Nish. photo provided by JEO

Example of a completed streambank stabilization on the West Nish as part of our RCPP. photo provided by JEO

In December 2025, Golden Hills hosted a streambank stabilization webinar led by John Thomas.

Additional Resources

Explore the links below to learn more about streambank stabilization and river restoration: 

• Roadside Guide to Clean Water: Streambank and Floodplain Restoration
• Iowa Learning Farms Virtual Field Day: Improving Water Quality in the East andWest Nishnabotna Watersheds
• Iowa Learning Farms Streambank Restoration resources
• ISU Webinar - Streambank Erosion: Causes, Impacts, and Control
  
• Iowa DNR River Restoration
• Iowa Stormwater Education Partnership - River & Stream Restoration
• MN DNR Resource Sheet: Streambank Erosion & Restoration