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Open-File Report O-20-04, Temporal and spatial changes in coastal morphology, Tillamook County, Oregon, by Jonathan C. Allan; 27 p. report, geodatabase, metadata.

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What's in This Report?

New lidar based mapping along the Tillamook County coast provides updated spatial extents of beaches and dunes that may be subject to existing and future storm-induced wave erosion, runup, overtopping, and coastal flooding. Side-by-side maps of the spatial extent of beaches and dunes in 1975 and now show changes that have taken place. These data will help communities implement Oregon Statewide Planning Goal 18: Beaches and Dunes.

Abstract:

The objective of this study was to produce updated information on the spatial extent of beaches and dunes in Tillamook County that may be subject to existing and future storm-induced wave erosion, runup, overtopping, and coastal flooding. These data are of importance to the Department of Land Conservation and Development and the seven coastal counties of Oregon in order to implement Statewide Planning Goal 18: Beaches and Dunes.

Oregon Statewide Planning Goal 18 requires local jurisdictions adopt a beach and dune overlay zone in their comprehensive plan, which may be used to manage development on or near beaches and dunes. Regional mapping of the coastal geomorphology of the Oregon coast to define the extent of its beaches and dunes was originally undertaken between 1972 and 1975 by the U.S. Department of Agriculture Soil Conservation Service (USDA, 1975). However, in the intervening 45 years, much has changed on the coast. Of particular importance has been the proliferation of European beach grasses that have helped stabilize many coastal dune systems, while many areas of the Tillamook County coastline have experienced significant erosion, especially since the late 1970s. In addition, new technologies such as lidar are now providing unprecedented levels of detail, enabling scientists to more accurately map the spatial extents of both the contemporary and historical foredune systems. These three factors combined necessitate that the USDA (1975) overlay zone be updated to reflect contemporary conditions. As a result of the updated mapping, our analyses indicate the following broad-scale changes: