Geomorphic Mapping for the lower Middle Fork Willamette River, Oregon in 2018 and 2020

Since 2008, large-scale restoration programs have been implemented along the Willamette River, Oregon, to address historical losses of floodplain habitats for native fish. For much of the Willamette River floodplain, direct enhancement of floodplain habitats through restoration activities is needed because the underlying hydrologic, geomorphic, and vegetation processes that historically created and sustained complex floodplain habitats have been fundamentally altered by dam construction, bank protection, large wood removal, land conversion, and other influences (for example, Hulse and others, 2002; Wallick and others, 2013). For gravel-bed rivers like the Willamette River, planimetric changes (defined here as geomorphic changes related to horizontal adjustments independent of elevation and that can be observed using aerial photographs and other two-dimensional maps) include changes in channel position, gravel bars, and side channels. Restoration activities likely to cause planimetric changes in channel features include revetment removal, construction of off-channels features, modifications to floodplain topography, and gravel pit enhancements. Repeat planimetric mapping, provides a basis for quantifying channel changes and relating those changes to restoration projects or other natural or anthropogenic influences affecting geomorphic processes. Repeat mapping also can be used to quantify planimetric  changes resulting directly from implementation of restoration projects, as well as subsequent geomorphic evolution of those features. 
In this study, repeat geomorphic mapping was completed for 2018 and 2020 along the lower 6.8 kilometers of the Middle Fork Willamette River (river mile 187.5 to 191.5 on USGS topographic maps) to support an assessment of geomorphic changes resulting from restoration activities implemented from 2014 to 2017. These datasets can be combined with previously published mapping (Keith and Gordon, 2019) in which the lower 11.6 km of Fall Creek and lower 27.3 km of Middle Fork Willamette were mapped for six periods (1936, 2005, 2011, 2012, 2014, and 2016). The 2018 and 2020 mapping was completed in the vicinity of large-scale restoration projects at the Willamette Confluence Preserve where gravel ponds and revetments were modified to improve floodplain habitats. The repeat mapping datasets include GIS layers defining the landforms and water features, as well as the types of cover and vegetation density on landforms, and types of secondary channel features mapped throughout the active channel. 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. Floodplain islands that have a substantial area surrounded by active channel features in the mapping were also included.

Tags: aerial-photography, channel-stability, floodplain-restoration, fluvial-geomorphology, geomorphology, geospatial-analysis, historical-channel-change, inlandwaters, jasper-oregon, landforms, lane-county, middle-fork-willamette-river, oregon, planimetric-change, restoration, sediment-transport, usgs-627173a0d34e76103cd58628
Organization: Department of the Interior