The active channel of the Willamette River in western Oregon is the portion of the floodplain that regularly conveys water and bed-material sediment (typically sand and gravel) on an annual basis (Wallick and others, 2013). The active channel comprises features such as gravel bars, side channels, main channel and alcoves that contribute to the overall diversity of aquatic and floodplain habitats (for example, Hall and others, 2007; Harrison and others, 2011; Williams and others, 2020). Historically, a complex mosaic of active channel features supported a diverse array of fish and wildlife, but over the last 170 years, construction of flood control dams, bank stabilization structures, removal of large wood and conversion of floodplain forests to agriculture and other land uses has resulted in substantial reductions in the complexity and abundance of active channel features (Sedell and Froggatt, 1984; Hulse and others, 2002; Baker and others, 2004; Wallick and others, 2013; Gregory and others, 2019).
For gravel-bed rivers like the Willamette River, active channel features such as gravel bars, side channels, and alcoves can be mapped remotely to evaluate the distribution of features along the river or to assess geomorphic changes over time. Digital geomorphic maps of features within the active channel of the Willamette River were developed to document channel conditions between the confluence of the Coast Fork and Middle Fork Willamette Rivers near Springfield (floodplain kilometer [FPKM] 228) and the head of the Newberg pool, where streamflow is backwatered by Willamette Falls, near Dayton (FPKM 80) in 2009 and 2016. This documentation describes the geomorphic mapping for the active channel of the Willamette River floodplain as mapped from aerial photographs acquired in the summer of 2009.