DEBRIS DAM DYNAMICS 


by Jim Yuskavitch 





Oregon Department of Fish and Wildlife Fish Restoration and Enhancement


Program grant helps restore natural food cycle to Knowles Creek in Lane County





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In scientific parlance, itÕs called trophic dynamics. But Charley Dewberry,


restoration coordinator for the Eugene-based conservation organization


Pacific Rivers Council, explains it more simply as Òwatershed digestion,Ó a


concept that is key for long-term recovery of salmon in Oregon.





Beginning in the early 1980s, Dewberry, along with other researchers, began


to conduct fish surveys in the lower Siuslaw River in the Oregon Coast


Range. ÒOver the years,Ó says Dewberry, Òwe found that the more coho salmon


there were, the smaller they were. And the fewer the fish, the larger they


were, suggesting food limitations.Ó In other words, there seemed to be only


enough food in the river system to sustain either a large number of small


fish or a few large ones. And with the natural reproduction of coho salmon


in the river basin at less than one percent of historic levels, this


new-found information suggested that simply restoring habitat without


investigating why there was a shortage of organic material to sustain the


salmon would not be enough to recover fish populations.





The answer to that question seems to lie largely in how surrounding forest


lands are managed, and how that management effects the rivers and streams


that flow through those forests.


ÒA lot of organic matter comes down through the stream channel from the


uplands in debris torrents,Ó explains Dewberry. ÒWhat I found was that


debris torrents differ significantly in managed forests than in old-growth


forests.Ó In a properly functioning stream system, these torrents would


occur at regular intervals, distributing organic material and nutrients


throughout the system, providing fish and other aquatic life with food. But


that did not appear to be happening in the Siuslaw basin.





The idea of stream trophic dynamics works something like this: winter


flooding would send logs, root wads and other debris careening downstream,


eventually jamming up to form debris dams. Like beads on a string, these


debris dams would form up and down the stream. Occasionally, high water


would break one of these dams, sending organic material downstream, Over


time, debris dams would continually form and break causing a relatively


constant flow of organic material to pass through the stream system. But,


unlike in old-growth forests, streams in managed forests typically do not


have logs, boulders and other instream structures to slow the velocity of


floodwaters or large trees in upland flat areas to absorb floodwaters. So


high water flows rush down the stream channel unimpeded, washing away


organic materials and nutrients. The theory was that a river systemÕs upland


areas could be ÒresetÓ in an attempt to recreate the natural cycle of


trophic dynamics.





In 1992, the Pacific Rivers Council, along with the Siuslaw National Forest


and Champion International began a cooperative project to apply this new


salmon restoration strategy on Knowles Creek, a tidewater tributary of the


Siuslaw River located on the timber companyÕs land in Lane County. Later,


Champion International was bought by the John Hancock Timber Management


Group which continued to be involved in the project.





They identified 28 upland flats that were not functioning properly because


there were no large logs or boulders in the stream to create the debris dams


critical to nutrient distribution. Over the past six years, the thrust of


the project has been to protect the less than five percent of the watershed


that is still intact to provide refuge areas for salmon, storm proofing


logging roads, which can send large amounts of sediment into streams during


wet weather and to recreate old-growth forest conditions along streamside


areas. These three areas are considered crucial to the success of the


project. To help this process along, John Hancock Timber Management Group


agreed not to harvest timber in the valley floors, or flats, and to plant


conifers in alder lowland areas.





Interestingly enough, placing instream structures is not part of the


project. ÒOur view,Ó says Dewberry, Òis that instream work is an emergency


measure while the stream is in recovery. The real recovery stuff is to keep


the healthy areas, bombproof roads and evaluate high-risk slide areas that


might blow out the stream. When the natural movement of debris is recovered,


we will have a more normal frequency and magnitude of debris torrents and


mature trees in the lowlands to hold them.Ó





Part of this effort was made possible by a $31,000 grant from the Oregon


Department of Fish and WildlifeÕs Fish Restoration and Enhancement Program.


The Fish Restoration and Enhancement Program was created by the Oregon


Legislature in 1989 and is funded by a surcharge on sport and commercial


fishing licenses and commercial poundage fees. The program is overseen by a


seven-member citizen board that reviews proposals and recommends funding for


fish restoration and enhancement projects throughout the state.





Although it is expected to take up to 100 years for the creek to completely


recover its trophic dynamics, early indications look very good. A record


drought in 1992 and a record flood in 1996 put the project through its


paces. The researchers found 85 percent of the Siuslaw basinÕs fish


population in the refuge areas demonstrating the value these areas have in


protecting fish during difficult times. Coho salmon production in the


Siuslaw River has averaged about 5,000. But it has hit the 15,000 mark twice


since the project was started. And chinook salmon production has gone from


23,000 to as high as 250,000 in 1995. ÒThat,Ó says Dewberry, Òis vindicating


our ideas on stream restoration.Ó





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For further information:   Charlie Corrarino, (503) 872-5252 ext. 5431,


Charley Dewberry, (541) 345-0119