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Date Permissions Signed

12-3-2020

Date of Award

Fall 2020

Document Type

Masters Thesis

Department or Program Affiliation

Department of Geology

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Grossman, Eric E.

Second Advisor

Pfeiffer, Allison

Third Advisor

Mitchell, Robert J. (Geologist)

Fourth Advisor

Crosby, Sean Christopher

Abstract

A primary threat to coastal regions is extreme water levels from tides, storm surges, and waves which drive coastal evolution. Predicting wave runup, the vertical extent of wave uprush on a beach above still water level, and the morphologic responses to storms within the Salish Sea is complex because of the high variability of shoreline exposure to waves and wind, morphology, coastal landforms, and tide range across the region. As part of a USGS study, this project was designed to assess how wave energy offshore drives runup, validate existing runup models (van der Meer, 2002; Stockdon et al., 2006; Didier et al., 2019; Roelvink et al., 2009 (Xbeach)), and create new parameterizations of runup with the deployment of an autonomous real time ground ubiquitous surveillance (ARGUS) imaging system. In-situ measurements of waves and remotely sensed measurements of wave runup were gathered between December 2018 and February 2020 on a ~1 km stretch of beach on west Whidbey Island, WA. Several photogrammetric approaches to characterize beach morphology were employed including structure-from-motion and Cobble Cam techniques. Additionally, I developed and tested a metric relating sediment size and sorting to pixel intensity of imagery from time-lapsed ARGUS imagery.

The results showed that simple parameterizations of runup have low to moderate performance compared to processed based models such as Xbeach for the Whidbey field site. The relationship between runup measurements and environmental parameters highlights the sensitivity of runup to slope and bed friction, with steeper and smoother beach slopes correlating to higher runup magnitudes. The rough low-tide terrace was shown to effectively dissipate wave energy diminishing runup. The results also show that runup can add an additional 1.6 m to total water levels which equates to 70% of the tidal range that is impacted by flooding, sediment movement, and erosion.

Storms in the region were strong enough to dramatically alter a beach in the matter of hours (erode or accrete bed levels by 10s cm). Observations showed that recovery of beach levels occurs rapidly (days). Cobble transport rates in the winter months ranged from 0.9 to 2.4 m/day in the direction of net shore-drift. Observed average erosion rates of a bluff landslide at the Whidbey field site ranged from 0 m/month to 0.82 m/month, with an average of 0.62 m/month and total lateral erosion of 7.3 m to 8.1 m over a 14-month period. Additionally, we found that small increases to water levels will dramatically increase the frequency water levels will reach the bluff toe (twenty times more often with 0.25 m of SLR expected by mid-century than 2019). Raising sea levels will therefore increase bluff erosion rates that drive sedimentation and morphology which alters nearshore habitat as well as increases coastal hazards.

Type

Text

Keywords

geology, coastal, waves, runup, sediment transport, bluff, erosion, recession, storm, morphology

Publisher

Western Washington University

OCLC Number

1226514673

Subject – LCSH

Geomorphology--Research--Washington (State)--Whidbey Island; Cliff ecology--Washington (State)--Whidbey Island; Sediment transport--Salish Sea (B.C. and Wash.); Ocean circulation--Salish Sea (B.C. and Wash.); Remote sensing--Salish Sea (B.C. and Wash.)

Geographic Coverage

Whidbey Island (Wash.); Salish Sea (B.C. and Wash.)

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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