Geomorphic Mapping of Fall Creek Lake, Oregon, 2016

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 to dam operations at Fall Creek Lake in which lake levels are temporarily lowered to streambed each fall or winter to facilitate downstream passage of juvenile spring Chinook salmon. Reservoir erosion during these streambed drawdown operations results in sediment delivery to downstream reaches. This study of geomorphic change is focused on the major alluvial channel segments downstream of the U.S. Army Corps of Engineers dams on Fall Creek and the Middle Fork Willamette River, as well as the 7.36 square kilometers Fall Creek Lake. This mapping, along with analyses of topographic change, were carried out to better understand patterns and processes of erosion within the reservoir that occur during streambed drawdowns and how they may relate to geomorphic changes in downstream reaches. This dataset consists of a single GIS layer defining the reservoir spatial domains, landforms, and substrates within the Fall Creek Lake reservoir. For this study, the reservoir mapping area boundary was defined by elevation, encompassing all landforms within maximum pool elevation of 254 meters (North American Vertical Datum of 1988) and extends about 10 kilometers from Fall Creek Dam upstream to Big Fall Creek Road bridge. The dataset was mainly developed by digitizing from orthophotographs and digital elevation models (DEMs) created from aerial photographs collected in November 2016 and supplemented with lidar data collected in January 2012.