Surficial Particle Count and Clay Horizon Marker Data for Fall Creek and the Middle Fork Willamette River, Oregon in 2015-2017

The Middle Fork Willamette River Basin encompasses 3,548 square kilometers of western Oregon and drains to the mainstem Willamette River. Fall Creek Basin encompasses 653 square kilometers and drains to the Middle Fork Willamette River. In cooperation with the U.S. Army Corps of Engineers, the U.S. Geological Survey evaluated geomorphic responses of downstream river corridors to annual drawdowns to streambed at Fall Creek Lake. This study of geomorphic change is focused on the major alluvial channel segments downstream of the U.S. Army Corps of Engineers dams including the lowermost 11.5 km of Fall Creek and 27.3 km of the Middle Fork Willamette River, as well as Fall Creek Lake. This dataset is delivered as one excel workbook with two tabs, and associated metadata includes separate entity sections for each workbook tab. These tables document grain-size distributions and sediment depths collected as a part of a study to document the geomorphic responses to the Fall Creek Lake streambed drawdowns. Surficial grain size distributions and fine sediment deposit depths were measured for this study over 2015 through 2017 to support analyses tracking geomorphic change in the reaches downstream of Fall Creek Lake. Particle counts were collected at 6 gravel bars along Fall Creek and the Middle Fork Willamette River in September 2015. Counts were repeated at 5 of those sites and at 5 additional sites along the Middle Fork Willamette River in October 2016. Multiple clay horizon markers were deployed at 10 sites in October 2015. Deposition depths were measured multiple times throughout the year. Clay horizon markers were deployed again at 9 of the 2015 sites plus one additional site in October-November 2016 and, again, measured throughout the year. Sediment measurements are summarized in spreadsheet tables.