The Key to CFC’s new Aquatic Restoration Program: Simple Tools and the Mind of a Beaver | Cascade Forest Conservancy

The Key to CFC’s new Aquatic Restoration Program: Simple Tools and the Mind of a Beaver

By Amanada Keasberry

June 30, 2021

In the coming years, scientists predict our region will continue to experience more frequent and intense droughts, floods, wildfires, insect outbreaks, and other harmful effects of climate change. CFC is working strategically to slow climate change and to build climate resilience where we can now. Restoring degraded ecosystems can help mitigate the climate related threats our region is facing at the local level. One of our newest restoration projects is helping restore aquatic habitats and ultimately benefiting the species that depend on them.

When rainfall and snowpack levels are below normal, it can lead to a water shortage that puts pressure on many species as well as downstream human communities. Additionally, a lack of water makes it easier for wildfire to spread. Droughts are not rare in the West, but climate change is making drought more prevalent and making it difficult for the landscape to recover. Washington, Oregon, and many other western states are in the midsts of potentially the longest drought in over a thousand years, coming off of one of the driest springs in the past century. Intense droughts are expected for this year and to continue for years to come.

Many of you are familiar with our beaver reintroduction project that aims to utilize beaver and their dam-building abilities to enhance the function of the surrounding ecosystem. Beaver dams help to retain more water in the form of ponds and side channels. Not only does the surface water increase, underground the water table gets replenished as well. A landscape that is well saturated above and below ground has the ability to stay wet throughout the year–even if rainfall and snowpack are low.

Due to the great benefit of beaver dams and the fact that sometimes beaver move on to new areas, researchers Michael Pollock, Tim Beechie and Chris Jordan came up with the idea to reinforce beaver dams by strategically placing wooden posts to help maintain their structure and function. Eventually, these researchers realized that they and other restoration-minded individuals could build a series of beaver-inspired dams themselves, and coined the structures “beaver dam analogues” or simply “BDAs”. Utilizing natural material to build simple, low-cost structures is a low-tech process-based restoration technique aimed at reestablishing the physical, chemical, and biological processes within a riverscape.

BDAs can be installed for a variety of reasons:

• to reinforce a pre-existing beaver dam

• to attract beavers to a particular stream

• to get the benefits of a beaver dam even if the area is not suitable for beavers  

Building a beaver dam analog takes minimal tools and the mind of a beaver. Typically a series of BDAs are needed to achieve the goal of increasing water storage capacity. The overall series of BDAs is far more important than the individual BDA. First, an analysis of your area of interest is needed to ensure the structures are being placed in the most optimal location of the stream where they will be most effective. For our upcoming project at Woods Creek, we worked with the environmental engineering firm, Interfluve, to help with the design and placement of the BDAs. BDAs can take many forms and shapes depending on the desired results within a particular system, but the type CFC will be installing is one of the more traditional designs. Untreated wooden posts are driven into the stream bed from bank to bank (Figure 1). Once the posts are installed, natural materials like sticks and rocks are collected from around the project site to finish the dam. Branches are woven between the posts and rocks and cobble are placed at the base of the posts (Figure 2). Once the structures are completed, results should be immediate. Water will begin to pool up behind the dam while letting fish and other aquatic species pass with ease (Figure 3). The true test of your construction will come during the winter months. They are installed knowing that they will not last forever, so maintaining them as long as you can is ideal. In some cases, you’ll have beavers come in and do the maintenance for you. For any structures that do fail, the wood used will end up somewhere downstream but won’t cause any negative impact to the system because only natural materials were used. 

Low-tech restoration projects are becoming increasingly popular and are needed in many smaller headwater streams that are already seeing the impacts of climate change. Stay tuned for the next blog in this series to learn more about our BDA project site at Woods Creek and why we choose this particular location to restore.