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DRAFT 



Table 3. Estimates of annual erosion and sediment runoff into streams from agricultural lands in the 

 Tillamook Bay Basin. Dau derived from 'Tillamook Bay Drainage Basin Erosion and Sediment Study, 

 Oregon-Main Report" (USDA-SCS, 1978). 



This information is pertinent to the accuracy of text references: 



'Total erosion averaged 0.6 tons/acre/year, 0.35 to 1.6 tons/acre/year 

 range. Related stream sediment loading rates averaged 0.4 

 tons/acre/year. ' 



The Departments' calculations indicate that total erosion is estimated at 0.46 

 tons/acre/year, with a range of 0,32 to 1.18 tons/acre/year, and with sediment loading 

 of 0.31 tons/acre/ year. 



More important, however, are the conclusions of the authors concerning the impacts of 

 agriculture on sedimentation processes in Tillamook Bay: 



"Stream bank and channel erosion from cattle are serious sedimentation 

 problems in the lower floodplain reaches of streams in the Tillamook Bay 

 Basin (USDA, SCS. 1978). Ninety percent of stream sediments 

 originating in these predominantly pasture lands come from stream bank 

 and channel erosion sources. " 



'Cattle move into channel bottoms... Banks and stream channel edges are 

 broken down and direct sedimentation occurs. Subsequently in storm 

 flows, stream bottom scour and constant bed gravel occur (ibid). ' 



This statement implies that sti^am bank erosion and the resultant sediment discharges 

 are strictly a result of stream side catUe use. This statement ignores text from the SCS 

 report which directly cautioned readers from making this assumption: "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 total sediment in the system is the crucial problem." The 

 SCS study documented significant sediment loads originating from forest lands (51,603 

 tons/year), and that a high proportion (8 to 66 percent range) of this material was 



A-58 



