I’ve watched heavy equipment dumping ton after ton of rock into the Yellowstone River in the valley below our office over the past month.  In this case, mostly replacing giant rock ‘barbs’ that were flanked and left mid-channel in the famed Yellowstone River during flooding in 2022.  All this cost and invasive activity intended to reduce local property erosion. 

Year-after-year, landowners and governments repeat this same, expensive ritual, hauling more quarried stone from miles away to protect ranches, homes, infrastructure or other property. 

In the 2022 500-year-flood event in the Upper Yellowstone, miles and miles of ‘rip-rap’ and ‘hard-armor’ failed wholly and catastrophically.  In many cases the rock structures were simply flanked and ultimately abandoned out in the river.  Giant sized rock barbs, revetments and more failed, forcing water behind all that placed rock further accelerating erosion and increasing property damages.

What’s happened on the Yellowstone River is a common, sad scenario in the U.S.

When stream banks and riparian vegetation suffer as a result of human impacts, the lack of native, woody vegetation and active floodplains accelerate rates of erosion. Concerns about loss of property or damaged buildings prompt calls for immediate action. The action most frequently taken is to slope back the eroding banks and then armor them with large quarried stone. It’s an expensive solution both economically and environmentally.

As expensive hard materials are installed, the energy of the water from one riprapped bank is deflected and displaced to another place on the stream, causing a domino effect as the trend to riprap rolls downstream.  

Rock begets more rock as landowners and municipalities try desperately to hold onto eroding soils. The cumulative result is a laterally-constrained river robbed of its floodplain and unable to maintain the fluvial processes that are essential to maintaining a dynamic and healthy river ecosystem. As more vegetation is replaced with rock, floodwaters rush over banks prompting the need for additional flood-retaining levees.

While hard armor (riprap, concrete, etc) can provide localized erosion control for stream banks, studies show that its use can cause undesirable consequences to fish and wildlife habitat and to the long-term health of river ecosystems. Such has been the recent fate for this prized resource. Such have been the cumulative impacts on the riparian habitats over much of the Upper Yellowstone Ecosystem.

In contrast, free-flowing rivers maintain natural flow regimes, which cue certain spawning, nesting, feeding, and migration behaviors for fish and wildlife. Certain plant species, such as cottonwoods, depend on the scour and deposition of floodwaters to create suitable germination sites.

Natural floodplains and riparian areas with healthy vegetation are able to absorb the force and volume of floodwaters by storing water and slowly releasing it back into the system. At the same time, plants filter water by trapping sediment and absorbing pollutants and excess nutrients, improving water quality. Deep-rooted woody plants anchor soil, preventing bank erosion while overhanging branches shade the banks reducing water temperatures. Colder water holds more life-giving oxygen. Leaves from plants are broken down by aquatic insects which, in turn, provide food for fish and other wildlife. Wild rivers provide critical habitat. Studies show that 80 percent of all wildlife species depend in some way upon riparian zones.

Besides providing water, healthy riparian zones provide shelter, food, shade, and migration corridors for wildlife. Migrating birds use riparian areas as stopover areas, often following river corridors hundreds of miles.

For decades, Trout Headwaters has pioneered and promoted low-cost biostabilization technologies to restore river banks, floodplains and properties. We recently published a case study providing an example of alternatives for the current, failing regime of rock armor on rivers like the Yellowstone. >Learn More