History, physical effects, and management implications of large organic debris in western Oregon streams

Large organic debris has historically been an importantelement in small mountain streams of the Pacific Northwest. Thedebris serves to slow the movement of water and inorganic and fineorganic matter through the channel. Debris may remain in the channelfor decades or longer, and tends to stabilize some sections of astreambed and streambanks while destabilizing other areas. The com-bination of clearcutting and the complete removal of large debris ina channel may deprive a stream of this natural feature of streams fora century or longer. The consequences are likely to be downcuttingand "channelization" of the stream, accelerated transport of fineorganic and inorganic sediment, and a possible decrease in biologicalproductivity of the stream ecosystem. Therefore, stream debris manage-ment during logging operations should include leaving undisturbed thenatural, stable organic debris in the channel.
The principal factors controlling the concentration, stability,and functions of stream debris are the history and condition of thesurrounding timber stand, flushing history of the channel, stability
and abundance of bedload material, steepness of the channel and adjacenthillslopes, and slope stability in the drainage. Because of thiscomplexity, each stream presents a unique situation which should beinspected in the field and considered on an individual basis before adebris management decision is made.
KEYWORDS: Stream environment -)debris, mass, movement, residue,western Oregon.
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