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FOREST PRACTICES 



Splash Dacn 



There are still lingering effects of splaBh dams and log driving in the 

 Chehalis Basin: (1) the stream bottom may have been scoured down to bedrock, 

 especially in the upper Chehalis and the South Fork; (2) the channel may have 

 been straightened; (3) pools may have been obliterated; and (4) creation of 

 new pools may be retarded by up to a century due to absence of sufficiently 

 large woody debris entering the stream. As a consequence, salmon spawning and 

 rearing habitat has not recovered (Jeff Cederholm, WDHR, pers. comm. ) • See 

 pages 18-19 for further discussion of splash dams. 



Logging-associated Landslides 



Logging-associated landslides most often are <\csocxated with failure of 

 logging roads, some of which are built on slopes whose stability cannot be 

 accurately predicted. During major rainstorms, some of these ongoing 

 landslides trigger sudden flows of boulders, trees, and smaller material into 

 streams. During these events, known as debris torrents, debris typically 

 travels down the streambed for less than a mile and creates a blockage. If 

 this jam is within an area formerly accessible to anadromoue fish, potential 

 habitat is lost, the degree of damage depending on the number of accessible 

 and useful miles upstream. Blockage may persist for a few days or many years, 

 until a subsequent high flows break the debris dam. Debris torrents also can 

 remove all potential spawning gravel, vegetative cover, and pool-maintaining 

 woody debris in their path. 



A clear example of an impassable debris jam exists on Thrash Creek, a 

 tributary of the upper Chehalis, (Bisson et al. 1986). Bisson (Weyerhaeuser 

 Co., pers. coma.) suggests that debris jams may also be affecting fish access 

 to parts of Cinnabar, George, and Big creeks. Warren Sorensen (Weyerhaeuser 

 Co., pers. comm.) observed evidence of fresh debris torrents on Swem, Smith, 

 and Ludwig creeks after the severe rainstorms of January and February of 1990. 



Streams made accessible by fish ladders or culverts are susceptible to 

 blockage by any form of accelerated erosion. Increases in large bed load — 

 that is, gravel, cobble, and boulders moving down the streambed — can plug, 

 bury, or otherwise destroy fish access. For example, on Roger Creek, a 

 tributary to the upper Chehalis, accelerated erosion rendered the fish ladder 

 at the creek mouth ineffective (Brian Benson, WDF, pers. comm.). 



Sedimentation 



Logging- induced sedimentation clearly reduces fish populations (Cederholm and 

 Reid 1987) by reducing watar circulation around eggs and alevins in the 

 spawning beds. Construction, use, and maintenance of forest roads contributes 

 sediment to streams by mass slope failures or surfaee erosion of the road. In 

 areas of steep slope and unstable soils, mass failures are often the primary 

 path, but in more stable areas, erosion of road surfaces may be the 



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