Beach and Shoreline Dynamics in the Cannon Beach Littoral Cell; Implications for Dune Management
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State of Oregon Oregon Department of Geology and Mineral Industries Brad Avy, State Geologist SPECIAL PAPER XX BEACH AND SHORELINE DYNAMICS IN THE CANNON BEACH LITTORAL CELL; IMPLICATIONS FOR DUNE MANAGEMENT by Jonathan C. Allan1, Laura L. Gabel1 and Fletcher O’Brien2 2018 1Oregon Department of Geology and Mineral Industries, Coastal Field Office, P.O. Box 1033, Newport, OR 97365 2Oregon Department of Geology and Mineral Industries, 800 NE Oregon Street, Suite 965, Portland, OR 97232 Beach and shoreline dynamics in the Cannon Beach littoral cell; Implications for dune management DISCLAIMER This product is for informational purposes and may not have been prepared for or be suitable for legal, engineering, or sur- veying purposes. Users of this information should review or consult the primary data and information sources to ascertain the usability of the information. This publication cannot substitute for site-specific investigations by qualified practitioners. Site-specific data may give results that differ from the results shown in the publication. Cover photograph: Oblique aerial photo of the Chapman Point beach, located immediately north of Ecola Creek, Clatsop County. Photo taken by D. Best, March 09, 2015. Oregon Department of Geology and Mineral Industries Special Paper XX Published in conformance with ORS 516.030 For copies of this publication or other information about Oregon’s geology and natural resources, contact: Administrative Offices 800 NE Oregon Street #28, Suite 965 Portland, OR 97232 Telephone (971) 673-1555 Fax (971) 673-1562 http://www.oregongeology.org http://egov.oregon.gov/DOGAMI/ Oregon Department of Geology and Mineral Industries Special Paper XX ii Beach and shoreline dynamics in the Cannon Beach littoral cell; Implications for dune management TABLE OF CONTENTS 1.0 Introduction ....................................................................................................................................... 9 2.0 Beach Processes on the Oregon Coast .............................................................................................. 12 2.1 Background ...................................................................................................................................... 12 2.2 Tides ................................................................................................................................................ 12 2.3 Waves .............................................................................................................................................. 17 2.4 Sediment Transport ......................................................................................................................... 20 2.5 Oregon Tsunami Hazards ................................................................................................................ 23 3.0 Oregon Coast Dunes – Process and Morphologies ............................................................................ 26 3.1 Oregon Dune Morphology............................................................................................................... 27 3.2 Wind Processes on the Oregon Coast ............................................................................................. 30 4.0 Coastal Geology and Geomorphology of the Cannon Beach Littoral Cell .......................................... 36 4.1 Local Geology .................................................................................................................................. 36 4.2 Provenance of Cannon Beach Sediments ........................................................................................ 39 4.3 Coastal Geomorphology .................................................................................................................. 41 4.4 Historical Coastal Changes .............................................................................................................. 43 5.0 Observations of Cannon Beach Changes: 1997-2016 ........................................................................ 50 5.1 Topographic Beach Mapping ........................................................................................................... 50 5.2 Beach Characterization.................................................................................................................... 54 5.3 Recent Beach and Shoreline Changes in the Cannon Beach Littoral Cell ........................................ 58 5.5 Sand Volume Changes in the Cannon Beach Littoral Cell ................................................................ 61 6.0 Dune Management Implications ...................................................................................................... 70 6.1 Background ...................................................................................................................................... 70 6.2 Extreme Wave Erosion .................................................................................................................... 71 6.3 Design Elevations for Dunes at Cannon Beach ................................................................................ 73 6.4 Disposal Approaches ....................................................................................................................... 73 6.5 Post-grading Responsibilities........................................................................................................... 74 6.6 Ecola Creek ...................................................................................................................................... 76 7.0 Conclusions ...................................................................................................................................... 80 8.0 References ....................................................................................................................................... 85 9.0 Appendices ...................................................................................................................................... 88 9.1 Appendix A: Cannon Beach Profiles ................................................................................................ 88 Oregon Department of Geology and Mineral Industries Special Paper XX iii Beach and shoreline dynamics in the Cannon Beach littoral cell; Implications for dune management LIST OF FIGURES Figure 1 Location map of the Cannon Beach littoral cell showing sub-cells, place names and beach profile locations. ...................................................................................................................... 11 Figure 2. Daily tidal elevations measured at South Beach, Newport on the central Oregon coast .............. 12 Figure 3. Seasonal cycles in monthly-mean water levels based on data from the Southbeach tide gauge (1967-2017) ................................................................................................................... 13 Figure 4. The trends of “winter (red)” and “summer (blue)” mean-sea levels measured by the Southbeach tide gauge ............................................................................................................ 14 Figure 5. Projected future changes in regional sea levels on the Oregon coast ........................................... 15 Figure 6. Assessments of changes in RSLs based on tide-gauge records compared with benchmark and GPS measurements of land-elevation changes, with their corresponding RSL rates obtained by adding the 2.28 mm/yr PNW eustatic rise in sea level ............................... 16 Figure 7. Seasonal variability of ocean waves measured offshore from Newport ........................................ 18 Figure 8. A) Comparisons of histograms (probability distributions) for the periods 1975–1990, 1990–2005, and 2006-2017 documenting the shift in the wave climate to higher waves. a) Standard probability distribution, b) number distribution plotted on a semi- log scale, and c) empirical cumulative distribution function. .................................................. 19 Figure 9. Patterns of sediment transport during “normal” (left) and El Nino (right) years ........................... 20 Figure 10. Top) The Pacific Decadal Oscillation (PDO) and the Multivariate El Niño (MEI) Index; red indicate positive ‘warm’ phase, blue indicate negative ‘cool’ phase. Gray shading indicates the ‘normal’ range of variability. Dashed lines reflect periods when the PDO switched between cool/warm phases. .................................................................................... 22 Figure 11. Aerial photos flown in 1939 and 1967 as well as lidar collected in 2009 depict the historical shoreline changes, dune stabilization and accompanying morphological changes in the beach and dunes at Chapman Point, Cannon Beach ....................................... 28 Figure 12. A) Conceptual model showing the relationship between sediment supply and vegetation that directly affects the geomorphology of dunes. B) Biophysical feedback associated with three dune grass species influence the dune morphology .............................................. 29 Figure 13. A) Wind roses showing the seasonal distributions of wind speeds by direction for the Newport, Oregon C-Man climate station operated by the National Data Buoy Center (NDBC). The direction in which the arms point reflects the direction in which the winds are blowing from; B) Seasonal wind speed empirical cumulative distribution function (ECDF); and C) diurnal pattern of mean wind