Dataset Information

Shortwave Sand Transport in the Shallow Surf Zone.

ABSTRACT: Empirical parameterizations of the shortwave sand transport that are used in practical engineering models lack the representation of certain processes to accurately predict morphodynamics in shallow water. Therefore, measurements of near-bed velocity and suspended sand concentration, collected during two field campaigns (at the Sand Engine and Ameland, the Netherlands) and one field-scale laboratory experiment (BARDEXII), were here analyzed to study the magnitude and direction of the shortwave sand flux in the shallow surf zone. Shortwave sand fluxes dominated the total sand flux during low-energetic accretive conditions, while the mean cross-shore current (undertow) dominated the total flux during high-energetic erosive conditions. Under low-energetic conditions, the onshore-directed shortwave sand flux scales with the root-mean-square orbital velocity urms and velocity asymmetry Au but not with the velocity skewness. Under more energetic conditions the shortwave flux reduces with an increase in the cross-shore mean current u¯ and can even become offshore directed. For all data combined, the contribution of the shortwave flux to the total flux scales with (-Auurms)/|u¯| , with a high contribution of the shortwave flux (?70%) when this ratio is high (? 10) and low contributions (?0%) when this ratio is low (?1). We argue that the velocity asymmetry is a good proxy for the net effect of several transport mechanisms in the shallow surf zone, including breaking-induced turbulence. These field and laboratory measurements under irregular waves thus support the hypothesis that the inclusion of velocity asymmetry in transport formulations would improve the performance of morphodynamic models in shallow water.

SUBMITTER: Brinkkemper JA

PROVIDER: S-EPMC6049877 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature

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Shortwave Sand Transport in the Shallow Surf Zone.

Brinkkemper J A JA Aagaard T T de Bakker A T M ATM Ruessink B G BG

Journal of geophysical research. Earth surface 20180528 5

Empirical parameterizations of the shortwave sand transport that are used in practical engineering models lack the representation of certain processes to accurately predict morphodynamics in shallow water. Therefore, measurements of near-bed velocity and suspended sand concentration, collected during two field campaigns (at the Sand Engine and Ameland, the Netherlands) and one field-scale laboratory experiment (BARDEXII), were here analyzed to study the magnitude and direction of the shortwave s ...[more]

PMID: 30034978

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Project description:Surf zones are highly dynamic marine ecosystems that are subject to increasing anthropogenic and climatic pressures, posing multiple challenges for biomonitoring. Traditional methods such as seines and hook and line surveys are often labor intensive, taxonomically biased, and can be physically hazardous. Emerging techniques, such as baited remote underwater video (BRUV) and environmental DNA (eDNA) are promising nondestructive tools for assessing marine biodiversity in surf zones of sandy beaches. Here we compare the relative performance of beach seines, BRUV, and eDNA in characterizing community composition of bony (teleost) and cartilaginous (elasmobranch) fishes of surf zones at 18 open coast sandy beaches in southern California. Seine and BRUV surveys captured overlapping, but distinct fish communities with 50% (18/36) of detected species shared. BRUV surveys more frequently detected larger species (e.g. sharks and rays) while seines more frequently detected one of the most abundant species, barred surfperch (Amphistichus argenteus). In contrast, eDNA metabarcoding captured 88.9% (32/36) of all fishes observed in seine and BRUV surveys plus 57 additional species, including 15 that frequent surf zone habitats. On average, eDNA detected over 5 times more species than BRUVs and 8 times more species than seine surveys at a given site. eDNA approaches also showed significantly higher sensitivity than seine and BRUV methods and more consistently detected 31 of the 32 (96.9%) jointly observed species across beaches. The four species detected by BRUV/seines, but not eDNA were only resolved at higher taxonomic ranks (e.g. Embiotocidae surfperches and Sygnathidae pipefishes). In frequent co-detection of species between methods limited comparisons of richness and abundance estimates, highlighting the challenge of comparing biomonitoring approaches. Despite potential for improvement, results overall demonstrate that eDNA can provide a cost-effective tool for long-term surf zone monitoring that complements data from seine and BRUV surveys, allowing more comprehensive surveys of vertebrate diversity in surf zone habitats.

Dataset Information

Shortwave Sand Transport in the Shallow Surf Zone.

Publications

Shortwave Sand Transport in the Shallow Surf Zone.

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