Catastrophic Beach Sand Losses Due to Erosion from Predicted Future Sea Level Rise (0.5–1.0 m), Based on Increasing Submarine Accommodation Spaces in the High-Wave-Energy Coast of the Pacific Northwest, Washington, Oregon, and Northern California, USA
Ken Scheidegger assisted with petrographic microscopic analyses of reference heavy-mineral grains. Mark Darienzo assisted with aerial photo/video analyses of beach widths and coastal physiography in the PNW study area. Phil Jackson assisted with directing beach profiling in the PNW study area. Jon Kimerling and Doann Hamilton, respectively, designed and populated the database used in the beach profiling aspects of this study. Debra Doyle completed the beach profiling in the Tillamook, Sand Lake, and Pacific City subcells. David Percy and Ken Cruikshank completed the beach profiling in the Netarts subcell. Gary Carver and Lori Dengler provided logistical support for beach profiling in the Orick and Eureka subcells. Jim Phipps, mike Roberts, Loraine Woxell, and April Herb assisted with beach profiling and subsurface testing in the Columbia River Littoral Cell system. Maureen Walczak assisted with sample selection from PacWave (2019) vibracore MSL1903-P1-2A22VC. Kennett Peterson assisted with early manuscript editing. This research was funded by the National Coastal Resources and Development Institute, under the Coastal Zone Management Program, Oregon, grants No. 2-5632-03 and CZ17.90-5635-01, and the U.S. Geological Survey, Coastal and Marine Geology Program, under the South West Washington Coastal Erosion Project, Co-op #1434-HQ-96- AG-01612, and the NOAA Office of Sea Grant and Extramural Programs, U.S. Department of Commerce, under grant number NA76RG0476, project number R/SD-04, and by appropriations made by the Oregon State Legislature.
Marine transgression, Stratigraphic geology, Bioaccumulation
The U.S. Pacific Northwest (PNW) coastline (1000 km) has been analyzed for conditions that could impact beach erosion from potential near-future (100 year) sea level rise (SLR). Heavy mineral analysis of river, beach, and shelf samples (n = 105) establish the sources of the beach deposits. River bedload discharge and intervening estuarine sinks for river sand supplies (n = 31) were normalized to the one century time interval. Twenty-six subcell beaches (657 km in combined length) were surveyed (153 profiles) for beach sand widths (20–412 m) and sand cross-sectional areas (20–1810 m2 ) above wave-cut platforms and/or 0 m tidal datum. Cross-sectional areas were multiplied by beach segments to yield subcell beach sand volumes (0.4 × 106 m3 –35.8 × 106 m3 ± 20% uncertainty). Innermost-shelf profiles were measured for distance to the 100-year depth of closure (30 m) to digitize the areas of inner-shelf accommodation space. Both innermost-shelf and estuarine accommodation space volumes for beach sand displacements were established for 0.5 and 1.0 m SLR. The existing subcell beach sand volumes and computed new beach sand supplies (rivers and longshore transport) were subtracted from the estimated sand volumes lost to submarine accommodation spaces to establish potential beach sand deficits from near-future SLR. Of the 26 surveyed active-beaches, some 60% and 80% (by length) are predicted to be lost, respectively, from the 0.5 m and 1.0 m SLR or equivalent littoral sand sedimentation in submarine accommodation spaces. Projected losses reach 90% for all PNW beaches (~900 km total length) from 1.0 m SLR. The computed beach sand deficits are used to estimate soft-sand retreat distances or erosional beach step backs (50–590 m ± 35% uncertainty) in unrevetted barrier spit and beach/dune deflation plains from 1.0 m SLR. Such empirical accommodation space analyses should have worldwide relevance to predicting beach erosion from near-future SLR.
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Peterson, C. D., Pettit, D. J., Kingen, K., Vanderburgh, S., & Rosenfeld, C. (2021). Catastrophic beach sand losses due to erosion from predicted future sea level rise (0.5–1.0 m), based on increasing submarine accommodation spaces in the high-wave-energy coast of the Pacific Northwest, Washington, Oregon, and Northern California, USA. Marine Geology, 439, 106555.