by Barry Olson, January 10, 2021

The Need for Engineered Large and Small Woody Debris Stream
Structures to Restore Streams and ESA Listed Fish Stocks

Through the media, fishermen and fisherwomen are made aware of the reasons for the decline of Pacific Northwest salmon because of over-harvest, habitat loss, climate change, and many others. In this article, I would like to share what I have learned from installing over 2500 engineered structures constructed using large and small woody debris. A structure is defined as a single or multiple LWD engineered structure. The featured structures were all constructed using mostly large woody debris. Constructing engineered structures are the “technique of choice” for the recovery of stream hydrological function and creating fish habitat. This habitat is needed for the recovery of Chinook, coho, sockeye, pink, chum, steelhead, and trout species. Engineered structure is the current structure term for artificially replacing the large and small woody debris that naturally built up in the stream-channels for hundreds, if not thousands of years. Most streams today are devoid of large and small woody debris and are little more than “a ditch” just rapidly moving water, especially during high flow and flood events.

Two of the featured structures are engineered log jams. This type of structure is used in the larger river channels to divert streamflow into a side-channel or when a main channel divides. It is also used in the larger, deeper rivers to form “holding areas” for both adult and juvenile fish moving up or down the river. Two of the other featured structures are called log weirs or sill logs. These structures are used to form resting pools, trap and hold a mixture of spawning gravels, cobble, and small boulders. The third featured structure is referred to as an upstream double deflector. This structure is used to direct streamflow to the center of the stream-channel away from the streambanks, to form a resting pool, and during high flow events, allow bedload to move through the channel. Woody debris is also used in the channel placed in many configurations to slow down the flow, divert the flow away from the streambanks and to provide hiding cover for both adult and juvenile fish. In my experience, I found that the weir, double and single deflector and cover structures were more effective in the streams and smaller rivers less than 60-80 feet wide. These structures are crucial for the successful migration of the fish and their recovery. I installed log weirs, deflectors, and cover structures in all sizes of streams to withstand normal and flood flows.

I am by education, and until 1983, was a forestry guy. That all changed with the passage of the National Forest Management Act in 1976. I was turned into a “fish guy”. All I knew at that time was that fish swam up and down the river and they sometimes ended up on my hook. Over the next 16 years I learned a lot about fish and how they used rivers, and utilized woody debris. I was given the task of learning how the sciences of forestry, fisheries and wildlife management, hydrology, and engineering interacted to restore fish and wildlife, and in the restoration of our streams, rivers, lakes and wetlands. Those 16 years became some of the most stressful, but ended up being the most satisfying years of my life. I didn’t realize that I was to be one of the early “on the job stream practitioners” of that time in Region 6 (Washington and Oregon) of the Forest Service. When I mean practice, I mean it because we tried all types of techniques to install engineered structures the imagination could think up. We shared techniques and toured other “restoration projects” throughout Washington and Oregon. We had both successes and failures, but we learned by doing. I included this paragraph to emphasize the way the sciences are needed to restore our fish and streams and to emphasize the lessons learned, often by trial and error. Restoring habitat that had been degraded for over century was a new policy change for the Forest Service. Very few people have had the opportunity to restore fish species and streams that I was given and to learn and apply the sciences together. We were less regulated then and were given more leeway. As a novice, I became very discouraged at times, but as, I tested and applied the sciences, I slowly learned what techniques worked and didn’t. Those techniques were tested by four “rain on snow flood events”. During this “learning phase”, I was later to realize that our combined team efforts of restoration and hatchery techniques resulted in reversing the decline of the fish in the tributary streams of the White River.

I have visited my restoration projects several times since I retired and in 2009 I was given the opportunity to find and evaluate approximately 2500 engineered structures. Overall, the majority of the structures were performing their function as designed and about 20% were washed away, buried, or repositioned. Structures of all types have been in position for 16 to 40 years. This is a remarkable achievement considering the structure designs, securing techniques, and placement within the stream channel were new and untested.

I hope this article has provided the reader with information that will give them encouragement that streams and fish stocks can be restored. We need to get beyond finger pointing and blame. It will take ALL of us to restore the historical fish runs. I know that they can be restored if we work together and learn from and apply “tested” techniques. Two ESA listed stocks that have been kept from becoming extinct are the White River Spring Chinook and the Baker River sockeye. They are not off the ESA list, but are two very good candidates for de-listing, given time.
In closing, I would like to encourage individuals to consider a career in the sciences I mentioned above, and to volunteer in helping to restore the habitat and fish species. The challenges and rewards are unlimited. It is very gratifying when you see fish utilizing newly created large and small woody debris habitat.

Special Note: The pictures of the featured structures were taken during summer low flow. They look more functional during higher flows.

About Barry Olson:

Barry Olson worked as a Forestry Technician and “On the Job Training” stream restoration specialist for the U.S. Forest Service on the Snoqualmie (formerly White River District) from 1976 through 2001. Experienced in Forestry, Fisheries, Hydrology, Contracting and Engineering Barry utilized research, visits to work sites performed by others, and in-house seminars, to plan and implement, Fish, Wildlife, and Watershed restoration projects.