Observations of mixing and transport on a steep beach

Continental Shelf Research
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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 (κxκy) 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.

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Publication type Article
Publication Subtype Journal Article
Title Observations of mixing and transport on a steep beach
Series title Continental Shelf Research
DOI 10.1016/j.csr.2019.03.009
Volume 178
Year Published 2019
Language English
Publisher Elsevier
Contributing office(s) St. Petersburg Coastal and Marine Science Center
Description 14 p.
First page 1
Last page 14
Country Untied States
State California
Other Geospatial Carmel River State Beach
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