Bank Stabilization

Explore the problems and solutions associated with stream channels by clicking through the slides using the slide-navigation buttons () below.

The Problem

When a river is being restored and the stream channel is realigned or left in place but reshaped, the new and disturbed stream banks need to be stabilized to keep them from eroding or collapsing. In fact, a restoration project can literally come apart if the new banks are not stabilized, a costly and potentially damaging event. Hence the need for bank stabilization structures, which can include rootwad revetments (revetment simply means wall or barrier) and large woody debris jams. Similar structures can be seen on natural, undisturbed streams (as shown in the photo above). Stream restoration specialist simply looked at how nature stabilizes stream banks and mimicked what they saw.

The Solutions

The problem of unstable banks on newly restored stream reaches has two primary solutions: rootwad revetments and large woody debris jams. Both are constructed out of natural, native materials. These channel structures have been used on streams and rivers of all sizes throughout the United States, and if properly designed and constructed, have survived major floods and other disturbances with little or no damage. Click below to learn more.

Rootwad Revetments

Rootwads are composed of the root mass or root ball of a large tree plus a portion of the trunk. They are used to armor a streambank by deflecting stream flows away from the bank. They also provide structural support for the streambank. By dissipating water velocities and erosive stresses along the bank, they protect the channel until dense riparian vegetation becomes established. Each revetment (the word revetment just means a barrier or retaining wall) will also generally have two to four mature willow transplants stuck into the root masses where the structure meets the streambank to speed revetation. Other plantings will help to improve the long-term stability of the bank.

How to Make a Rootwad Revetment in 5 Easy Steps

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Large Woody Debris Jams

Large woody debris (LWD) has many uses in stabilizing stream banks and providing aquatic habitat. They are built to mimic naturally occurring wood jams that form in the lower half of outside meander arcs and consist of several large trees, various-sized rootwads, small diameter woody material, and large anchor rocks. The large trees are trenched into the bank and anchored with the rocks. Other woody material is then interlaced to create a diverse array of woody material. Several rootwads and logs are extended out into the channel to diversify aquatic habitat. Over time, the jams grow in size as they capture more woody debris transported during high water.

How to Make a Large Woody Debris Jam in 6 Easy Steps

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The Benefits

While the main purpose of bank-placed rootwads and large woody debris jams is to protect and stabilize stream banks until dense riparian vegetation can become established, they also provide other benefits critical to a healthy stream. For example, they increase the diversity of fish habitat by providing overhead cover in the stream and by diversifying water flow paths, which creates all kinds of micro-habitats in the stream. They provide hiding places for fish of all sizes and visual separation for fish. They also maintain deep pools and provide foodweb functions such as trapping and retaining organic matter. What's more, these bank-protection structures provide habitat for mammals, birds, and insects as well as areas where fine sediments can settle out, which further benefits fish.