Understanding sandbar dynamics and variability is integral to developing a predictive
capacity for nearshore flows, sediment transport, morphological change, and
ultimately for determining coastline exposure to damaging storm waves. Along the
high-energy U.S. Pacific Northwest (PNW) coast, sandbars typically dominate the
bathymetry of the active zone. Here we report on a nearshore bathymetric data set that
covers an exceptionally long stretch of coast and crosses several littoral cell
boundaries. Our study area stretches from Point Grenville, Washington to Cascade
Head, Oregon, including 8 littoral cells and approximately 250 km in the alongshore.
We describe and quantify the morphological variability of sandbars in the PNW over
large spatial scales as well as attempt to explain the inter-littoral cell variability via
trends and variability in environmental parameters. From 560 bathymetric profiles
(~1000 km of measurements) we have extracted over 500 distinct subtidal sandbars.
The bar zone extends to over 1km from the shoreline in the northern part of the study
area, but only to about 600m in the southern part. Maximum bar crest depths are
typically 7m below MLLW. Bar heights range from a step in the cross-shore profile to
over 3m from crest to trough. The northernmost littoral cells typically have two or
more bars per cross-shore profile whereas the littoral cells in the southern part of our
study area have only one bar. The mean depths of the bars, however, are much more
consistent across littoral cells. The mean depths remain consistent even while the
upper shoreface slope significantly increases from north to south, requiring that the
maximum bar distance from the shoreline decreases from north to south. This regional
gradient in upper shoreface slope is likely a response, at least in part, to a general
coarsening trend in the sediment from north to south and hence linked to variations in
regional geology. / Graduation date: 2013
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36079 |
| Date | 28 November 2012 |
| Creators | Di Leonardo, Diana R. |
| Contributors | Ruggiero, Peter |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Relation | North Coast Explorer |
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