Predicted Responses of Beaches, Bays, and Inner-Shelf Sand Supplies to Potential Sea Level Rise (0.5-1.0 m) in Three Small Littoral Subcells in the High-Wave-Energy Northern Oregon Coast, USA

Authors

Curt D. Peterson, Portland State UniversityFollow
Debra Lee Doyle, Portland State University
Charles L. Rosenfeld, Oregon State University
Kara E. P. Kingen, Portland State UniversityFollow

Sponsor

The research is financed by the National Coastal Resources and Development Institute, and the NOAA Office of Sea Grant and Extramural Programs.

Published In

Journal of Geography and Geology

Document Type

Article

Publication Date

2020

Subjects

Coastal erosion -- Effect of global warming on, Coastal archaeology, Eolian processes

Abstract

Three small subcells (Nehalem, Tillamook, and Netarts) totaling ~55 km shoreline length in the high-wave energy northern Oregon coast are evaluated for potential beach sand loss from sea level rise (SLR) of 0.5–1.0 m during the next century. The predicted erosion is based on beach sand displacement from the narrow beaches (average ~120 m width) to increased submarine accommodation spaces in the innermost-shelf (to 30 m water depth) and in the subcell estuaries (Tillamook Bay, Netarts Bay, and Nehalem Bay), following predicted near-future SLR. Beach sand sources from local rivers, paleo-shelf deposits, and/or sea cliff retreat are discriminated by distinctive heavy-mineral tracers. Modern beach sands in the study area are derived from river sand (~75 %) and paleo-shelf sand (~25 %). The supplies of paleo-shelf sand to the beaches have largely diminished in late-Holocene time. The river-enriched beach sands have been transported offshore to the inner-shelf (0–50 m water depth) to fill increasing accommodation space in the inner-shelf during latest-Holocene conditions of relative SLR (1.0 m ka-1). To evaluate the beach sand response to future SLR, representative beach profiles (n=17) and intervening beach segment distances were compiled to yield beach sand volumes above mean lower low water (MLLW) or shallower wave-cut platforms 'bedrock'. Across-shore cross-sectional areas, as averaged for each subcell, are as follows; Cannon Beach (304 m²), Tillamook (683 m²), and Netarts (227 m²). Littoral sand displacements to the adjacent innermost-shelf (to 30 m water depth) and the marine-dominated areas of the three estuaries are based on assumed vertical sand accretion rates of 1.0 m per century and a conservative value of 0.5 m per century. The filling of such submarine accommodation spaces will displace all active-beach sand reserves in all three subcells for either the 1.0 m or 0.5 m thickness accommodation space scenarios. Large beach sand deficits, primarily from the filling of offshore accommodation spaces, could cause further retreat of soft-shorelines, including barrier spit and beach plain/dune deposits, in the Tillamook subcell (150-280 m) and in the southern half of the Netarts subcell (370-770 m). The accommodation space approach used to predict beach sand volume loss from future SLR should have broad applicability in complex littoral systems worldwide.

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Copyright for this article is retained by the author(s), with first publication rights granted to the journal.

This work is licensed under a Creative Commons Attribution 4.0 International License.

Description

The data that supports this article is available in PDXScholar and can be found here: 10.15760/geology-data.01

Locate the Document

https://doi.org/10.5539/jgg.v12n2p1

DOI

10.5539/jgg.v12n2p1

Persistent Identifier

https://archives.pdx.edu/ds/psu/35045

Citation Details

Peterson, C. D., Doyle, D. L., Rosenfeld, C. L., Kingen, K., (2020). Predicted Responses of Beaches, Bays, and Inner-Shelf Sand Supplies to Potential Sea Level Rise (0.5-1.0 m) in Three Small Littoral Subcells in the High-Wave-Energy Northern Oregon Coast, USA. Journal of Geography and Geology. Vol. 12, No. 2.