Portland State University PDXScholar Dissertations and Theses Dissertations and Theses Winter 4-10-2015 Landforms along the Lower Columbia River and the Influence of Humans Charles Matthew aC nnon Portland State University Follow this and additional works at: http://pdxscholar.library.pdx.edu/open_access_etds Recommended Citation Cannon, Charles Matthew, "Landforms along the Lower Columbia River and the Influence of Humans" (2015). Dissertations and Theses. Paper 2231. This Thesis is brought to you for free and open access. It has been accepted for inclusion in Dissertations and Theses by an authorized administrator of PDXScholar. For more information, please contact [email protected]. Landforms along the Lower Columbia River and the Influence of Humans by Charles Matthew Cannon A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geology Thesis Committee: Andrew G. Fountain, Chair Jim E. O’Connor Scott F. Burns Portland State University 2015 Abstract River systems, such as the Columbia River in the Pacific Northwest, USA have been influenced by human activities, resulting in changes to the physical processes that drive landform evolution. This work describes an inventory of landforms along the Columbia River estuary between the Pacific Ocean and Bonneville Dam in Oregon and Washington. Groupings of landforms are assigned to formative process regimes that are used to assess historical changes to floodplain features. The estuary was historically a complex system of channels with a floodplain dominated by extensive tidal wetlands in the lower reaches and backswamp lakes and wetlands in upper reaches. Natural levees flank most channels in the upper reaches, locally including areas of ridge and swale topography and crevasse splays that intrude into backswamps. Other Holocene process regimes affecting floodplain morphology have included volcanogenic deltas, tributary fans, dunes, and landslides. Pre-Holocene landforms are locally prominent and include ancient fluvial deposits and bedrock. Historical changes to streamflow regimes, floodplain isolation by flood-control systems, and direct anthropogenic disturbance have resulted in channel narrowing and limited the amount of floodplain that can be shaped by flowing water. Floodplain isolation has caused relative subsidence of tidal floodplains along much of the lower estuary. Most extant landforms are on trajectories controlled by humans and new landforms are mostly created by humans. i Acknowledgements Charles (“Si”) Simenstad, Jennifer Burke, Mary Ramirez, and Danelle Heatwole at University of Washington School of Aquatic and Fishery Sciences; Jim O’Connor at USGS; and Keith Marcoe at Lower Columbia Estuary Partnership were collaborators on the Classification mapping. Jonathon (“Eric”) Stautberg, Jim O’Connor, Xavier Rodriguez Lloveras, and Joseph (“JoJo”) Mangano assisted with fieldwork. Lighthawk Aviation volunteer pilots Jim Richards and Jane Rosevelt provided flights over the estuary for oblique aerial photography. Reviews by Paul Pedone, John Christy, and Mackenzie Keith improved the Classification mapping on which this thesis is based. ii Table of Contents Abstract ............................................................................................................................................. i Acknowledgements ........................................................................................................................... ii List of Figures ................................................................................................................................. viii List of Tables .................................................................................................................................... x Chapter 1: Introduction ..................................................................................................................... 1 Columbia River Estuary Ecosystem Classification ........................................................................ 1 Setting of the Columbia River Basin and Estuary ......................................................................... 3 Drainage Basin and Geologic Setting ........................................................................................ 3 Late Quaternary Geologic Setting ............................................................................................. 7 Hydrology .................................................................................................................................. 7 Basin hydrology ..................................................................................................................... 7 Historical Floods .................................................................................................................... 9 Tides .................................................................................................................................... 12 Flow Regime Changes and Modern Hydrology ................................................................... 14 Sediment ................................................................................................................................. 15 Hydrogeomorphic Reaches ..................................................................................................... 16 Reach A ............................................................................................................................... 17 Reach B ............................................................................................................................... 19 Reach C .............................................................................................................................. 21 Reach D ............................................................................................................................... 22 Reach E ............................................................................................................................... 23 Reach F ............................................................................................................................... 24 iii Reach G .............................................................................................................................. 25 Reach H ............................................................................................................................... 25 Chapter 2: Geomorphic Mapping .................................................................................................... 27 Source Data for Geomorphic Mapping ........................................................................................ 27 Topography and Bathymetry ................................................................................................... 27 Columbia River Datum ............................................................................................................ 30 Mapping methods ....................................................................................................................... 31 Mapping Extent ....................................................................................................................... 31 Geomorphic Catenae and Ecosystem Complexes .................................................................. 33 Cultural Features ..................................................................................................................... 41 Chapter 3: Description and Interpretation of Mapping .................................................................... 42 Channel and Backwater Complexes ........................................................................................... 42 Primary channel ...................................................................................................................... 42 Permanently flooded ............................................................................................................ 42 Deep channel ...................................................................................................................... 43 Intermittently exposed .......................................................................................................... 43 Tributary delta ...................................................................................................................... 44 Intermittently exposed bedrock ............................................................................................ 44 Secondary channel .................................................................................................................. 45 Backwater embayment ............................................................................................................ 46 Tributary Channel .................................................................................................................... 47 Deep Channel ...................................................................................................................... 47 Side channel ........................................................................................................................ 48 iv Channel bar ......................................................................................................................... 48 Intermittently exposed bedrock ............................................................................................ 49 Tributary secondary channel 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