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Open-File Report O-14-02, Evaluation of erosion hazard zones for the dune-backed beaches of Tillamook County, Oregon, by Laura L. Stimely and Jonathan C. Allan

thumbnail image of OFR O-14-02 Order publication CD, $30, from Nature of the Northwest.
CD contains a 113-page report PDF, Esri ArcGIS® 10.1 geodatabase, and Microsoft Excel spreadsheet. Contents of CD-ROM are listed below.

Executive Summary:

This report describes and documents a range of coastal erosion hazards zones determined for the Tillamook County coastline, which may be used for general hazard planning purposes. The hazard zones were determined using two approaches:

The final derived hazard zones reflect the combined effect of both sets of processes.

Processes driving coastal change are exceedingly complex, making future predictions of erosion challenging. With that in mind, 83 scenarios of future coastal change were developed: 81 scenarios were developed using three beach-dune juncture elevations (EJ), three TWLs, and SLR projections for 2030, 2050, and 2100; two other scenarios incorporate the effects of regional subsidence due to the occurrence of a Cascadia subduction zone (CSZ) earthquake and the effects of a single storm. From modeled beach and dune erosion data we identified six scenarios (out of the suite of 81) for the purposes of defining future erosion hazard zones for the dune-backed beaches of Tillamook County. The recommended zones include:

A sixth hazard zone was defined using a technique developed by Kriebel and Dean (1993) to account for the fact that storms are rarely capable of fully eroding a dune (as predicted by the geometric model) due to their limited storm duration. Overall, the Kriebel and Dean approach yielded generally narrower hazard zones (~up to 22 m [72 ft] wide) for Tillamook County. Because the Oregon coast rarely experiences a single event over an entire winter season, the actual degree of erosion associated with a major storm(s) is likely to span the spectrum between the duration-limited storm-induced erosion calculated using Kriebel and Dean and the maximum potential erosion (DEMAX) defined using the geometric model. From our modeling, we argue that the Kriebel and Dean model is suitable for defining the minimum width of a coastal erosion setback zone for Tillamook County, while the other five hazard zones provide more conservative calculations of future erosion potential.

Example figure:

Figure 5-1. New dune-backed hazard zones for Neskowin, Tillamook County.

Figure 5-1, New dune-backed hazard zones for Neskowin, Tillamook County

CONTENTS OF CD-ROM:

GEODATABASE:

TillamookCountyErosionHazardZonesDatabase.gdb is an Esri® ArcGIS® version 10.1 geodatabase:
Feature class, polygons: TillamookCountyHazardZones_Active_Allan_Priest_2001
Feature class, polygons: TillamookCountyHazardZones_BluffBacked_Allan_Priest_2001
Feature class, polygons: TillamookCountyHazardZones_DuneBacked
Feature class, polylines: TillamookCountyHazardZones_DuneBacked_AllScenarios
Feature class, polylines: TillamookCountyHazardZones_Kreibel_and_Dean
Feature class, polylines: TillamookCountyHazardZones_LandwardEj
See metadata embedded in geodatabase for more information.

SPREADSHEET:

TillamookErosionHazardZonesData2014.xlsx is a Microsoft® Excel® spreadsheet listing morphology parameters and erosion distances at each dune-backed transect along the Tillamook County shoreline.

REPORT:

PDF-format 113-page report text in high- and low-resolution versions:

O-14-02_print.pdf
O-14-02_onscreen.pdf