Current and Historic Coastal Geomorphic (Feeder Bluff) Mapping of San Juan County, Washington Prepared for: Friends of the San Juans By: Coastal Geologic Services, Inc. Andrea MacLennan, MS Jim Johannessen, MS, LEG Stephanie Williams, BS/BA September, 2010 COASTAL GEOLOGIC SERVICES, INC. TABLE OF CONTENTS Table of Tables...................................................................................................iii Table of Figures ..................................................................................................v APPENDIX 1: Map Folio.....................................................................................v INTRODUCTION ..................................................................................................1 PURPOSE ..................................................................................................................................................... 1 BACKGROUND............................................................................................................................................. 1 Bedrock Geology .................................................................................................................................... 1 San Juan Islands and Puget Sound Bluffs and Beaches ......................................................................... 2 Net Shore-drift........................................................................................................................................ 4 Shore Modifications................................................................................................................................ 5 Coastal Processes and Nearshore Habitat............................................................................................. 5 Climate Change and Sea Level Rise....................................................................................................... 6 San Juan County Coastal Processes....................................................................................................... 7 San Juan County Nearshore Habitats .................................................................................................... 7 METHODS............................................................................................................9 PURPOSE AND RATIONALE .......................................................................................................................... 9 CURRENT CONDITIONS MAPPING ................................................................................................................ 9 Mapping Segments.................................................................................................................................. 9 Ancillary Data ...................................................................................................................................... 12 Field Mapping Procedure and GIS Processing.................................................................................... 13 Parcel Processing................................................................................................................................. 13 HISTORIC CONDITIONS MAPPING .............................................................................................................. 14 Historic Sediment Source Index (HSSI)................................................................................................ 14 RESTORATION AND CONSERVATION PRIORITIZATION ............................................................................... 18 Individual Unit Prioritization............................................................................................................... 18 Drift Cell Prioritization........................................................................................................................ 18 RESULTS ...........................................................................................................20 ISLAND SUMMARIES OF CURRENT AND HISTORIC COASTAL GEOMORPHIC MAPPING ............................... 20 Orcas Island ......................................................................................................................................... 20 Clark Island.......................................................................................................................................... 25 Obstruction Island................................................................................................................................ 25 Blakely Island ....................................................................................................................................... 26 Decatur Island...................................................................................................................................... 28 Center Island ........................................................................................................................................ 30 Lopez Island ......................................................................................................................................... 31 Shaw Island .......................................................................................................................................... 36 Turn Island ........................................................................................................................................... 38 Brown Island ........................................................................................................................................ 39 San Juan Island .................................................................................................................................... 40 Pearl Island .......................................................................................................................................... 46 Henry Island......................................................................................................................................... 47 Stuart Island ......................................................................................................................................... 49 Johns Island.......................................................................................................................................... 51 Waldron Island ..................................................................................................................................... 51 SUMMARY OF COUNTYWIDE CURRENT AND HISTORIC COASTAL GEOMORPHIC MAPPING ....................... 54 Feeder Bluffs ........................................................................................................................................ 54 Accretion Shoreforms ........................................................................................................................... 59 Transport Zones.................................................................................................................................... 60 1711 Ellis St, Suite 103, Bellingham, WA 98225 (360) 647-1845 www.coastalgeo.com Current and Historic Geomorphic Mapping of San Juan County, WA Page ii COASTAL GEOLOGIC SERVICES, INC. Shore Modifications.............................................................................................................................. 61 RESTORATION AND CONSERVATION PRIORITIZATION .............................62 RESTORATION BLUFFS .............................................................................................................................. 62 RESTORATION DRIFT CELLS...................................................................................................................... 65 CONSERVATION BLUFFS............................................................................................................................ 67 CONSERVATION DRIFT CELLS ................................................................................................................... 71 CONCLUSIONS .................................................................................................73 CONCLUSIONS .................................................................................................73 REFERENCES ............................................................................................................................................. 74 APPENDIX 1: Map Folio....................................................................................76 Current and Historic Geomorphic Mapping of San Juan County, WA Page iii COASTAL GEOLOGIC SERVICES, INC. Table of Tables Table 1. Major bedrock terranes of the San Juan Archipelago....................................................................... 2 Table 2. Geologic Units of San Juan County. See Map 1............................................................................... 3 Table 3. Current conditions field mapping criteria..........................................................................................12 Table 4. Available data for analysis of historic conditions of San Juan County. ............................................16 Table 5. Historic Sediment Source Index score sheet ...................................................................................17 Table 6. Historic shoretype delineations based on HSSI scores. ..................................................................18 Table 7a. Orcas Island drift cell descriptions .................................................................................................22