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 OPEN FILE REPORT O-17-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 2017 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 surveying 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 Open File Report O-17-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 Open-File Report O-17-XX ii Beach and shoreline dynamics in the Cannon Beach littoral cell; Implications for dune management TABLE OF CONTENTS 1.0 Introduction ....................................................................................................................................... 1 2.0 Coastal Geology and Geomorphology of the Cannon beach littoral cell ............................................. 4 2.1 Local Geology .................................................................................................................................... 4 2.2 Provenance of Cannon Beach Sediments .......................................................................................... 6 2.3 Coastal Geomorphology .................................................................................................................... 9 2.4 Coastal Change ................................................................................................................................ 11 2.5 Oregon Tsunami Hazards ................................................................................................................ 18 3.0 Beach Change Observations ............................................................................................................. 21 3.1 Topographic Beach Mapping ........................................................................................................... 21 3.2 Beach Characterization.................................................................................................................... 25 3.3 Recent Beach and Shoreline Changes in the Cannon Beach Littoral Cell ........................................ 29 3.5 Sand Volume Changes in the Cannon Beach Littoral Cell ................................................................ 32 4.0 Beach processes on the Oregon coast .............................................................................................. 42 4.1 Background ...................................................................................................................................... 42 4.2 Tides ................................................................................................................................................ 42 4.3 Waves .............................................................................................................................................. 48 4.4 Sediment Transport ......................................................................................................................... 51 4.5 Extreme wave erosion ..................................................................................................................... 54 5.0 Dune Management Implications ...................................................................................................... 57 5.1 Wind Processes on the Oregon Coast ............................................................................................. 58 5.2 Oregon Dune Morphology............................................................................................................... 64 5.3 Cannon Beach Dune Management Strategies ................................................................................. 66 6.0 Conclusion ........................................................................................................................................ 73 7.0 References ....................................................................................................................................... 78 8.0 Appendices ...................................................................................................................................... 82 8.1 Appendix A: Cannon Beach Profiles ................................................................................................ 82 Oregon Department of Geology and Mineral Industries Open-File Report O-17-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. ........................................................................................................................ 3 Figure 2. Haystack Rock at Cannon Beach. Homes present along the shore have been constructed on marine terrace deposits that form low, well vegetated bluffs ............................................. 5 Figure 3. Gravel beach at Arch Cape ............................................................................................................... 6 Figure 4. Variations in the percent abundances of various heavy minerals observed on the central to northern Oregon coast .......................................................................................................... 8 Figure 5. Geomorphic classification of the Canon Beach litteral cell (Cape Falcon to Tillamook Head). ....................................................................................................................................... 10 Figure 6. Oblique view looking toward west-northwest over downtown Cannon Beach toward Chapman Point ......................................................................................................................... 13 Figure 7. Variability in historical shoreline positions at Cannon Beach (1926–2009). .................................. 14 Figure 8. Long- (1800s through 2002) and short-term (1960s through 2002) shoreline change rates (solid black line) for the Cannon Beach littoral cell ........................................................ 15 Figure 9. Variability in historical shoreline positions at Arch Cape, 1926–2009 ........................................... 16 Figure 10. Variability in historical shoreline positions at Falcon Cove (1926–2009) ..................................... 17 Figure 11. The Trimble R7 base station antenna in operation on the Clatsop Plains ................................... 22 Figure 12. A 180-epoch calibration check is performed on a survey monument.......................................... 23 Figure 13. Plot showing beach/dune junctures (stars) identified from various surveys at the Cannon Beach 35 profile site. .................................................................................................. 26 Figure 14. Alongshore changes in beach slopes (tan β), beach/dune juncture (Ej) elevations, and dune/bluff crest/tops along the Cannon Beach cell ................................................................ 28 Figure 15. A) Recent landsliding at the south end of Falcon Cove (A) and from bluff erosion in the north (B) is actively supplying new sediment (predominantly gravels) to the littoral system ...................................................................................................................................... 29 Figure 16. Measured beach morphological changes carried out between 1997 and 2016 for selected sites in the Cannon Beach cell ................................................................................... 30 Figure 17. Net shoreline excursions along the Cannon Beach littoral cell as measured at the 6m (19.7 ft) contour for the period 1997–2009 ............................................................................. 31 Figure 18. Beach sand volume compartments identified for the Cannon Beach littoral cell showing the net sand volume change from 1997 to 2016 ...................................................... 35 Figure 19. Beach volume changes in the Cannon Beach littoral cell, divided into 10 sub-regions ............... 38 Figure 20. Sand elevation changes in the Chapman Point (left) and Presidential (right) dune management areas from 1997 to 2009 ................................................................................... 39 Figure