Fall Creek and Middle Fork Willamette Geomorphic Mapping Geodatabase

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. GIS layers defining the landforms, cover type, vegetation density, and secondary water type throughout the active channel study area were developed for six time periods: 1936, 2005, 2011, 2012, 2014, and 2016. GIS layers defining the wetted channel centerline throughout the active channel study area were developed for three time periods: 1936, 2005, and 2016. For this study, the active channel was defined as area typically inundated during annual high flows and includes the low-flow channel as well as side channels, and gravel bars. We also include floodplain islands that have a substantial area surrounded by active channel features in the mapping. The datasets were developed by digitizing from aerial photographs. Aerial photographs from 1936 were scanned, rectified, and mosaicked for this project. Digital channel traces were also produced to depict channel conditions along Fall Creek and the Middle Fork Willamette River floodplains from historical surveys. Plan and profile maps from 1926 (USGS, 1927) provide a basis from which to evaluate spatial and temporal changes that may result from multiple factors and place changes such as aggradation related to annual drawdown to streambed at Fall Creek Lake within historical context. GIS layers defining the outline of the 1926 Middle Fork Willamette River from the confluence with the Coast Fork Willamette River to the North Fork of the Middle Fork Willamette River were digitized. See individual FGDC metadata xml files for more information on the specifications, location, attributes and definitions, and processing descriptions.