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Scientific Investigations Report 2012–5200

Prepared in cooperation with the Cities of Damascus, Gresham, Happy Valley, Milwaukie, and Portland; Clackamas County Water Environment Services; Multnomah County; and the East Multnomah Soil and Water Conservation District

Suspended-Sediment Characteristics of the Johnson Creek Basin, Oregon, Water Years 2007–10

By Adam J. Stonewall and Heather M. Bragg

Thumbnail of and link to report PDF (3.25 MB) Significant Findings

An analysis of suspended-sediment transport in the Johnson Creek basin, Oregon, during water years 2007–10 indicated that:

  • Streamflow characteristics for the 4 years of study were not extremely dry or wet, and represented near-average conditions.
  • Computed average annual suspended-sediment loads were 1,890 and 4,640 tons at the Gresham and Milwaukie stations, respectively.
  • More than 70 percent of suspended-sediment transport in the watershed occurred during the high-flow months of November, December, and January.
  • Less than 10 percent of suspended-sediment transport in the watershed occurred during April–October.
  • About 50 percent of all suspended-sediment load is transported during the highest 1 percent of streamflows.
  • The January 2009 streamflow peak was the third highest in the 70-year record for Johnson Creek. About 50 percent of suspended-sediment transport in water year 2009 occurred in January.
  • The drainage area upstream of the Gresham streamflow-gaging station constitutes about 30 percent of the drainage area at the Milwaukie station, but accounted for about 40 percent of the suspended sediment and 45 percent of the streamflow at the Milwaukie station.
  • On an annual basis, most of the higher sediment yield at the Gresham station, relative to the Milwaukie station, can be explained by the higher streamflow yield at the Gresham station rather than by higher suspended-sediment concentration.

First posted October 3, 2012

For additional information contact:
Director, Oregon Water Science Center
U.S. Geological Survey
2130 SW 5th Avenue
Portland, Oregon 97201

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Suggested citation:

Stonewall, A.J., and Bragg, H.M., 2012, Suspended-sediment characteristics for the Johnson Creek basin, Oregon, water years 2007–10: U.S. Geological Survey Scientific Investigations Report 2012-5200, 32 p.

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