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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5187

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Suspended-Sediment Yields

Suspended-sediment yields (SSY) were calculated by dividing the estimated annual suspended-sediment loads (SSL) by the area, in square miles, of each subbasin. Normalizing the annual SSL by the respective subbasin areas provides additional context for the events discussed in section, “Suspended-Sediment Loads.”

The peak storms of water years 1999 and 2000 demonstrate the effect that a small subbasin, such as that upstream from Blowout (26 mi²), can have on sediment production in the North Santiam River basin. Although the highest SSL for water year 1999 was recorded at Breitenbush, the SSL at Blowout resulted in three times the sediment per unit area (fig. 13). The estimated 800 tons/mi² was the highest SSY for any of the stations for any of the water years during the study. The Breitenbush River produced the highest SSY for water year 2000, with an annual SSL of 74,700 tons resulting in an SSY of 705 tons/mi² (fig. 13). The highest SSY for water year 2002 was produced by the Blowout Creek subbasin. The road failure and debris flow upstream of the monitoring station resulted in relatively high SSY (520 tons/mi²) in a near average streamflow year (fig. 13). None of the monitoring stations in the North Santiam River basin recorded notably high SSY values during water years 2001, 2003, or 2004 (fig. 13).

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