Figure 3. Changes in bed-sediment grain size at one study location on the lower Elwha River, 1.5 km downstream of the Elwha Dam site. (a) When dam removal began in September 2011, the riverbed at this site consisted largely of coarse cobbles, typical of “armored”, coarse bed sediment such as is commonly found below dams. (b) By April 2012, new mud (derived from erosion of formerly trapped reservoir sediment) had been deposited in interstitial spaces between cobbles. (c) In August 2012, bed sediment contained new sand and gravel approximately 10 cm thick, with several rocks from the pre-dam-removal cobble bed still visible.
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