DYNAMIC REVETMENTS FOR COASTAL EROSION IN OREGON Final Report SPR 620 DYNAMIC REVETMENTS FOR COASTAL EROSION IN OREGON Final Report SPR 620 by Jonathan C. Allan, Ron Geitgey, and Roger Hart Oregon Department of Geology and Mineral Industries, Coastal Field Office, 313 SW 2nd St, Suite D Newport, OR 97365 for Oregon Department of Transportation Research Unit 200 Hawthorne Avenue SE, Suite B-240 Salem, OR 97301-5192 and Federal Highway Administration 400 Seventh Street SW Washington, DC 20590 August 2005 Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. FHWA-OR-RD-06-03 4. Title and Subtitle 5. Report Date August 2005 DYNAMIC REVETMENTS FOR COASTAL EROSION IN OREGON 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Jonathan C. Allan, Ron Geitgey, and Roger Hart Oregon Department of Geology and Mineral Industries Coastal Field Office, 313 SW 2nd St, Suite D, Newport, OR 97365 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Oregon Department of Transportation Research Unit 11. Contract or Grant No. 200 Hawthorne SE, Suite B-240 Salem, Oregon 97301-5192 SPR 620 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Oregon Department of Transportation Final Report Research Unit and Federal Highway Administration 200 Hawthorne SE, Suite B-240 400 Seventh Street SW 14. Sponsoring Agency Code Salem, Oregon 97301-5192 Washington, DC 20590 15. Supplementary Notes 16. Abstract Gravel beaches have long been recognized as one of the most efficient forms of “natural” coastal protection, and have been suggested as a form of shore protection. “Cobble berms,” “dynamic revetments” or “rubble beaches” involve the construction of a gravel beach at the shore, in front of the property to be protected. These structures are effective in defending properties because the sloping, porous cobble beach is able to disrupt and dissipate the wave energy by adjusting its morphology in response to the prevailing wave conditions. Dynamic revetments are much easier and cheaper to construct than a conventional riprap revetment or seawall. They are also aesthetically pleasing compared with “hard” engineered solutions. There remain, however, unanswered questions about their design particularly along the high-energy Oregon coast – the sizes and types of gravel to be used, their slopes and crest elevations, the volume of material to be included in the berm, and where the material may be obtained to construct such features. This study involved an examination of the morphological and sedimentary characteristics at 13 naturally occurring gravel beach study sites along the Oregon coast. Heights of the gravel beaches ranged from 5.7 to 7.1 m (19-23 ft), while the slopes of the beaches varied from 7.7º to 14.1º. Mean grain-sizes were found to range from -4.9Ø (30 mm) to -7.0Ø (128 mm), and were classified as well sorted to moderately well sorted. However, a comparison of these parameters among stable versus eroding gravel beaches revealed no clear discernable pattern. A key difference in the stability of the gravel beaches was the volume and width of gravel contained on the beach, with beaches containing larger volumes of gravel (> 50 m3.m-1 (538 ft3.ft-1)) and larger widths (> 20 m (66 ft)) being the most stable. Based on this analysis, a crest elevation of ~7.0 m (23 ft), mean grain-size of no less than -6.0Ø (64 mm), and a beach slope of 11º was recommended in future designs of dynamic revetments for the Oregon coast. While numerous quarry sites were identified that could supply crushed rock for the building of a dynamic revetment, rounded gravels were more difficult to locate and tended to be located farthest from the coast, increasing the costs that would be incurred to transport the material. 17. Key Words 18. Distribution Statement Dynamic revetment, gravel beaches, sediments, erosion, coastal Copies available from NTIS, and online at engineering, design, beach profiles, sediment sources, quarries http://www.oregon.gov//ODOT/TD/TP_RES/ 19. Security Classification (of this report) 20. Security Classification (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 108 Technical Report Form DOT F 1700.7 (8-72) Reproduction of completed page authorized Α Printed on recycled paper i SI* (MODERN METRIC) CONVERSION FACTORS APPROXIMATE CONVERSIONS TO SI UNITS APPROXIMATE CONVERSIONS FROM SI UNITS Symbol When You Know Multiply By To Find Symbol Symbol When You Know Multiply By To Find Symbol LENGTH LENGTH In Inches 25.4 Millimeters Mm mm millimeters 0.039 inches in Ft Feet 0.305 Meters M m meters 3.28 feet ft Yd Yards 0.914 Meters M m meters 1.09 yards yd Mi Miles 1.61 Kilometers Km km kilometers 0.621 miles mi AREA AREA In2 square inches 645.2 Millimeters squared mm2 mm2 millimeters squared 0.0016 square inches in2 ft2 square feet 0.093 Meters squared m2 m2 meters squared 10.764 square feet ft2 Yd2 square yards 0.836 Meters squared m2 ha hectares 2.47 acres ac Ac Acres 0.405 Hectares Ha km2 kilometers squared 0.386 square miles mi2 Mi2 square miles 2.59 Kilometers squared km2 VOLUME ii VOLUME mL milliliters 0.034 fluid ounces fl oz fl oz fluid ounces 29.57 Milliliters mL L liters 0.264 gallons gal Gal Gallons 3.785 Liters L m3 meters cubed 35.315 cubic feet ft3 ft3 cubic feet 0.028 Meters cubed m3 m3 meters cubed 1.308 cubic yards yd3 Yd3 cubic yards 0.765 Meters cubed m3 MASS NOTE: Volumes greater than 1000 L shall be shown in m3. g grams 0.035 ounces oz MASS kg kilograms 2.205 pounds lb Oz Ounces 28.35 Grams G Mg megagrams 1.102 short tons (2000 lb) T Lb Pounds 0.454 Kilograms Kg TEMPERATURE (exact) T short tons (2000 lb) 0.907 Megagrams Mg °C Celsius temperature 1.8C + 32 Fahrenheit °F TEMPERATURE (exact) °F Fahrenheit 5(F-32)/9 Celsius temperature °C temperature * SI is the symbol for the International System of Measurement (4-7-94 jbp) ACKNOWLEDGEMENTS We would like to sincerely thank the Oregon Department of Transportation Research Unit and the Federal Highways Administration for funding this study (contract no: 21019). In particular, we are grateful for the assistance (and patience) provided by Dr. Matthew Mabey. This work was also partially funded under the National Shoreline Erosion Control Development and Demonstration Program (Section 227) authorized by the Water Resources and Development Act of 1996 (Public Law 104-303, 110 Stat. 3658), under contract number W912HA-04-C-0028. We are grateful for the assistance provided by Dr. Don Ward and Mr. Bill Curtis from the Engineer Research Development Center (ERDC) of the U.S. Army Corps of Engineers. We would also like to acknowledge the help provided by Dr. Alan Niem, who assisted us with portions of the fieldwork and Dr. Paul Komar for his advice and comments on the study. We are also grateful to the members of the Technical Advisory Panel for their comments on the draft report. DISCLAIMER This document is disseminated under the sponsorship of the Oregon Department of Transportation and the United States Department of Transportation in the interest of information exchange. The State of Oregon and the United States Government assume no liability of its contents or use thereof. The contents of this report reflect the views of the author(s) who are solely responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official policies of the Oregon Department of Transportation or the United States Department of Transportation. The State of Oregon and the United States Government do not endorse products of manufacturers. Trademarks or manufacturers’ names appear herein only because they are considered essential to the object of this document. This report does not constitute a standard, specification, or regulation. iii An example of cross-shore sorting of sediments at Cove Beach, Oregon iv DYNAMIC REVETMENTS FOR COASTAL EROSION IN OREGON TABLE OF CONTENTS EXECUTIVE SUMMARY ......................................................................................................... ix 1.0 INTRODUCTION..................................................................................................................1 2.0 BEACH PROCESSES ON THE OREGON COAST.........................................................3 2.1 INTRODUCTION ...............................................................................................................3 2.2 LONGSHORE SEDIMENT TRANSPORT........................................................................5 2.3 PACIFIC NORTHWEST WAVE CLIMATE.....................................................................8 2.3.1 Wave Climate Characteristics .....................................................................................9 2.4 TIDES ................................................................................................................................13 3.0 GRAVEL BEACHES, COBBLE BERMS AND DYNAMIC REVETMENTS.............15 3.1 BEACH MORPHODYNAMICS ......................................................................................17 3.2 THE DYNAMIC REVETMENT CONCEPT ...................................................................20 3.3 DESIGN OF COBBLE BERMS/DYNAMIC REVETMENTS........................................22 3.4 EXISTING DYNAMIC REVETMENT APPLICATIONS ..............................................24 4.0 METHODS – MORPHOLOGY SURVEYS AND WAVE RUNUP CALCULATIONS...............................................................................................................27