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In some areas, timber harvest has necessitated the building of thousands of 

 miles of unpaved roads. High levels of sediment loading into watershed 

 streams have resulted from improperly constructed cuts, fills, and cross 

 drainage structures related to road building and maintenance. Even when 

 state-of-the-art procedures were used, road construction in steep terrain 

 has scarred watersheds, increasing sediment loading into streams for many 

 years. 



Sedimentation has impacted salmon and steelhead trout by creating a chain 

 reaction of ecological changes. Deep pools that provided cool refuges for 

 fish have been partially or totally filled, eliminating critical pre- 

 spawning and over-summering habitat. Spawning riffles have been choked 

 with fine sediment that has prevented spawning, killed eggs and prevented 

 newly hatched juvenile fish from emerging into the water column. Sediment 

 clogged riffles have reduced or eliminated production of aquatic insects 

 that are an important component of the diet of salmon and steelhead. 



Inappropriate timber harvest practices can change the runoff pattern in 

 some watersheds, creating higher flood flows and lower summer base flows. 

 Higher peak flows have changed the natural channel morphology (typically 

 widening and incising the channel), creating severe overwintering stress on 

 juvenile fish. At the other end of the hydrograph, reduced summer low 

 flows in the modified channel are not adequate to maintain fish habitat 

 during what is typically the bottleneck lifestage. 



Streamside vegetation has too often been cleared during logging or grazing 

 operations, reducing stream shading, increasing water temperatures to 

 undesirable levels which in turn have caused dissolved oxygen levels to 

 decline. In addition, the natural long-term recruitment of large trees and 

 root wads into a stream has been curtailed. During the past 20 years, 

 salmonid biologists have become aware that this "large organic debris," in 

 appropriate 2unount8, is one of the most important determinants of fish 



67-643 0-93-3 



