Observations of mixing and transport on a steep beach
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Authors
Brown, Jenna A.
MacMahan, Jamie H.
Reniers, Ad J.H.M.
Thornton, Ed B.
Shanks, Alan L.
Morgan, Steven G.
Gallagher, Edie L.
Subjects
Steep beach
Surfzone
Dye
Mass transport
Dispersion
Diffusion
Surfzone
Dye
Mass transport
Dispersion
Diffusion
Advisors
Date of Issue
2019
Date
2019
Publisher
Elsevier
Language
Abstract
Surfzone mixing and transport on a sandy, steep (∼1/8 slope), reflective beach at Carmel River State Beach, California, are described for a range of wave and alongshore flow conditions. Depth-limited wave breaking occurred close to the shore due to the steepness of the beach, creating a narrow surf/swash zone (∼10 m wide). Fluorescent Rhodamine dye was released as a slug in the surfzone, and the temporal and spatial evolution was measured using in-situ dye sensors. Dye concentration measured as a function of time reveals sharp fronts that quickly decay resulting in narrow peaks near the dye release, which subsequently broaden and decrease in peak concentration with alongshore distance. The measurements indicate two stages of mixing and transport occur inside the surfzone on the steep beach. 1) In the near-field (<50 m downstream of the dye release location), the dye fully mixed throughout the water column after a few incident waves then continued to disperse in two dimensions, with both advection and diffusion processes being important. 2) In the far-field (>50 m downstream from the dye release location), the mass transport was dominated by advection. The distance to the far-field is much shorter in the alongshore on a steep beach compared with a dissipative beach. Estimates of cross-shore and alongshore diffusion coefficients (κₓ, κᵧ) were found to be similar in magnitude within the surfzone. Outside the surfzone in the far-field, the results suggest that the mixing processes are independent of those inside the surfzone. The mixing and transport of material observed on this steep beach are found to be analogous to that previously measured on dissipative beaches, however the diffusion coefficients within and outside the surfzone were found to be smaller on this steep beach.
Type
Article
Description
The article of record as published may be found at http://dx.doi.org/10.1016/j.csr.2019.03.009
Series/Report No
Department
Oceanography
Organization
Naval Postgraduate School (U.S.)
Identifiers
NPS Report Number
Sponsors
National Science Foundation (OCE0926750)
Department of Defense through the National Defense Science and Engineering Graduate (NDSEG) Fellowship
Department of Defense through the National Defense Science and Engineering Graduate (NDSEG) Fellowship
Funder
Naval Research (ONR DURIP #N0001409WR20268)
Format
14 p.
Citation
Brown, Jenna A., et al. "Observations of mixing and transport on a steep beach." Continental Shelf Research 178 (2019): 1-14.
Distribution Statement
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.