Suspended-Sediment Loads

Annual SSL totals were computed for water years 2005–08 for each monitoring station for which streamflow and turbidity data were available (fig. 9). The error bars indicate the 90 percent prediction interval estimates for each annual SSL value.

For the low annual mean and peak streamflow in water year 2005, the SSL values were the lowest for the 4 years analyzed. In water year 2006, SSL at Breitenbush and Blowout was the highest of the 4 water years. SSL at North Santiam also was high in water year 2006, but was highest in water year 2007 because of the Mount Jefferson debris flow and subsequent storm event. SSL was highest during water year 2007 for all lower basin stations for the 4 water years. The streamflow conditions during water year 2008 resulted in lower SSL values than might be expected for an above-average mean flow year. The lack of significant peak streamflows resulted in SSL totals at all seven monitoring stations that were only slightly higher than those during the much lower streamflow in water year 2005.