Wave attenuation in the shallows of San Francisco Bay

Coastal Engineering
By:  and 



Waves propagating over broad, gently-sloped shallows decrease in height due to frictional dissipation at the bed. We quantified wave-height evolution across 7 km of mudflat in San Pablo Bay (northern San Francisco Bay), an environment where tidal mixing prevents the formation of fluid mud. Wave height was measured along a cross shore transect (elevation range−2mto+0.45mMLLW) in winter 2011 and summer 2012. Wave height decreased more than 50% across the transect. The exponential decay coefficient λ was inversely related to depth squared (λ=6×10−4h−2). The physical roughness length scale kb, estimated from near-bed turbulence measurements, was 3.5×10−3 m in winter and 1.1×10−2 m in summer. Estimated wave friction factor fw determined from wave-height data suggests that bottom friction dominates dissipation at high Rew but not at low Rew. Predictions of near-shore wave height based on offshore wave height and a rough formulation for fw were quite accurate, with errors about half as great as those based on the smooth formulation for fw. Researchers often assume that the wave boundary layer is smooth for settings with fine-grained sediments. At this site, use of a smooth fw results in an underestimate of wave shear stress by a factor of 2 for typical waves and as much as 5 for more energetic waves. It also inadequately captures the effectiveness of the mudflats in protecting the shoreline through wave attenuation.

Study Area

Publication type Article
Publication Subtype Journal Article
Title Wave attenuation in the shallows of San Francisco Bay
Series title Coastal Engineering
DOI 10.1016/j.coastaleng.2016.03.008
Volume 114
Year Published 2016
Language English
Publisher World Scientific Pub.
Contributing office(s) Pacific Coastal and Marine Science Center
Description 10 p.
First page 159
Last page 168
Country United States
State California
Other Geospatial San Francisco Bay, San Pablo Bay
Online Only (Y/N) N
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
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