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DRAFT 



survival. The Alsea Watershed Study (Moring 1975a) documented increased sediment 

 loading of 11-175% associated with logging and 54-205% associated with logging road 

 building. Phillips et al.(1975) documented 80% reduction in survival of alevins with 

 50% fine sediment. 



Tillamook Bay Erosion Studv (pages 173-174): 



The authors use a portion of the information contained in the SCS report (USDA-SCS 

 1978) to imply that the agricultural industry is the primary contributor to sediment 

 problems in the Tillamook Bay basin: 



'Stream sediments from agriculture were twice that from forests in the 

 Tillamook Bay drainage basin on a unit area basis (Table S-10). " 



"A significant difference between agricultural and forest stream sediment 

 contribution was the relative amount of eroded materials that entered 

 streams. In agriculture, 70 percent of eroded sediments become fluvial 

 sediments; in forestry, however, only 20 percent become fluvial 

 sediments. " 



These statements are based upon an incomplete discussion of the study, and ignore the 

 contribution that sediments (particularly bedload material) from upstream areas can 

 have on the acceleration of stream bank erosion in downstream reaches. The majority 

 of the fluvial sediment originating from the agricultural lands was due to stream bank 

 erosion (approximately 88 percent). The SCS report cautioned that: "forest lands and 

 croplands have been separated in the study for inventory and analysis. The two areas 

 are not independent, however; upstream problems can either amplify or reduce 

 downstream problems." The SCS report further noted that terrestrial sources of 

 sediment "...serves as an abrasive agent to increase the effectiveness of the flowing 

 water as an erosive agent." The autfiors failure to recognize that upstream activities on 

 forest lands may have affected stream bank erosion on agricultural lands results in 

 conclusions that are not supported by the SCS study. 



An alternate analysis of the relative impact of each land use activity could be achieved 

 by eliminating stream bank erosion from the total sediment estimates (Table 4): 



A-60 



