Effects of Southern California Kelp Beds on Waves

Elwany, M. Hany S.; O’Reilly, W. C.; Guza, R. T.; Flick, Reinhard E.

doi:10.1061/(asce)0733-950x(1995)121:2(143)

Cited by 65 publications

(42 citation statements)

References 12 publications

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“…Although previous field studies have shown that currents are reduced within kelp forests (Jackson 1998;Gaylord et al 2007), ocean swell propagates through kelp forests with little damping (Elwany et al 1995). Wake production of turbulence due to relative motion between kelp and water under waves may therefore be the main source of turbulent kinetic energy and associated mixing within dense kelp stands.…”

Section: Lsũmentioning

confidence: 94%

“…These periodic forces may alter the properties of waves as they propagate through kelp forests. Previous studies that have measured waves with bottom-mounted pressure sensors have not observed measurable changes in wave periods or amplitudes within kelp forests (Elwany et al 1995;Rosman et al 2007). However, more detailed measurements of wave properties, such as wave orbital velocities and propagation speeds, within kelp forests are currently lacking.…”

mentioning

confidence: 86%

“…Because turbulent kinetic energy scales with U 2 , turbulence generation from the mean flow could be quite small within kelp forests (Rosman et al 2010). However, waves propagate through kelp forests with minimal damping (Elwany et al 1995), and turbulence is generated by relative motion between kelp and water due to waves even if currents are small. Laboratory results suggest that vertical mixing due to wake turbulence is largest within and immediately below the surface canopy.…”

Section: Lsũmentioning

confidence: 99%

“…Field observations and modeling efforts indicate that wave energy loss during propagation across kelp forests is typically small-only a few percent of the incident wave energy flux (Elwany et al 1995;Gaylord et al 2003). Therefore, wave heights within kelp forests are similar to those offshore.…”

mentioning

confidence: 99%

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Interaction of waves and currents with kelp forests (Macrocystis pyrifera): Insights from a dynamically scaled laboratory model

Rosman

Denny

Zeller

et al. 2013

Limnology & Oceanography

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The interaction of surface waves and currents with kelp forests was examined under controlled conditions using a dynamically matched 1/25-scale physical model in a laboratory flume. In experiments with kelp mimics, waves increased the time-averaged drag by a factor of 2 and altered the shape of current profiles. Relative motion between model kelp and water under waves increased wake generation of turbulence, resulting in turbulent kinetic energies 2-5 times larger, and eddy viscosities 20-50% larger, than for experiments without waves. Because mixing lengths were reduced to wake-scales in the model kelp forest, eddy viscosities were 25-50% smaller than when kelp was absent. In the model kelp-forest surface canopy where solid obstacles were most densely spaced, wave orbital velocities were reduced by , 10% from linear wave theory predictions. This decrease in wave orbital velocities is thought to result primarily from inertial forces exerted on water by model kelp. Stokes drift was reduced by , 20% as a result of the change in wave orbital velocities. Although hydrodynamics within kelp forests are more complex than in the laboratory experiments and a wide range of flow conditions can occur, laboratory results suggest that (1) kelp forest drag is increased by waves; (2) wave properties can be altered by drag and inertial forces; and (3) wake production of turbulence caused by waves may be the main source of turbulence in dense kelp stands. Interactions between kelp and waves must therefore be taken into account when developing models for drag and mixing in these systems.

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Section: Lsũmentioning

confidence: 94%

mentioning

confidence: 86%

Section: Lsũmentioning

confidence: 99%

mentioning

confidence: 99%

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Interaction of waves and currents with kelp forests (Macrocystis pyrifera): Insights from a dynamically scaled laboratory model

Rosman

Denny

Zeller

et al. 2013

Limnology & Oceanography

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“…While some species, such as Cabomba caroliana, Nympheae rubra, and Eichinodorus grandifloru (Penning et al 2009), Laminaria hyperborea (Dubi and Torum 1995;Mork 1996), Macrocystis pyrifera (Elwany et al 1995;Elwany and Flick 1996), Posidonia oceanica (Gacia and Duarte 2001;Stratigaki et al 2009), Spartina alterniflora (Möller et al 1996(Möller et al , 1999, and Zostera marina (Fonseca and Cahalan 1992;Ifuku and Hayashi 1998), have been characterized for energy dissipation parameters, many more species have no information available. Establishing the relationships of drag to the Reynolds number (Re), using the orbital velocity and vegetation diameter as the characteristic length, and Keulegan-Carpenter number (KC), using the orbital velocity and vegetation diameter as the characteristic length, have also been attempted with some success (Mendez and Losada 2004;Augustin et al 2009), but there has not been strong evidence which one of these non-dimensional parameters is better suited to represent drag for plants (USACE 2006).…”

Section: Introductionmentioning

confidence: 99%

Flume instrumentation for measurement of drag on flexible elements under waves

2014

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Understanding energy dissipation by vegetation is critical for the effective management of shoreline erosion. Current methods for estimating energy dissipation require plant-specific parameters that are difficult to estimate for the large variety of plant morphologies used in shoreline protection, requiring testing on each species of interest. A simple and fast method to characterize drag in terms of wave interaction and obstruction natural frequency is needed to fully explore drag forces on vegetation. Our method directly measures hydrodynamic forces on individual plant shoots using a torque sensor mounted beneath the bed of a flume. This sensor allows data to be collected simply and inexpensively with high temporal accuracy that provides insight into drag forces and torque frequency from a variety of flexible elements when coupled with wave monitoring. The technique can evaluate several types of obstructions quickly without the need to set up an entire obstruction field. The data collected also suggest that more flexible objects result in less drag force on each element and suggest that frequency response is related to the frequencies existing in the driving wave and the natural frequency of the obstruction element, although harmonic synchronization appears to occur in some cases doubling the expected drag force magnitude.

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Seagrass blade motion under waves and its impact on wave decay

2017

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The hydrodynamic drag generated by seagrass meadows can dissipate wave‐energy, causing wave decay. It is well known that this drag depends on the relative motion between the water and the seagrass blades, yet the impact of blade motion on drag and wave‐energy dissipation remains to be fully characterized. In this experimental study, we examined the impact of blade motion on wave decay by concurrently recording blade posture during a wave cycle and measuring wave decay over a model seagrass meadow. We also identified a scaling law that predicts wave decay over the model meadow for a range of seagrass blade density, wave period, wave height, and water depth scaled from typical field conditions. Blade flexibility led to significantly lower drag and wave decay relative to theoretical predictions for rigid, upright blades. To quantify the impact of blade motion on wave decay, we employed an effective blade length, le, defined as the rigid blade length that leads to equivalent wave‐energy dissipation. We estimated le directly from images of blade motion. Consistent with previous studies, these estimates showed that the effective blade length depends on the dimensionless Cauchy number, which describes the relative magnitude of the wave hydrodynamic drag and the restoring force due to blade rigidity. As the hydrodynamic forcing increases, the blades exhibit greater motion. Greater blade motion leads to smaller relative velocities, reducing drag, and wave‐energy dissipation (i.e., smaller le).

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Effects of Southern California Kelp Beds on Waves

Cited by 65 publications

References 12 publications

Interaction of waves and currents with kelp forests (Macrocystis pyrifera): Insights from a dynamically scaled laboratory model

Interaction of waves and currents with kelp forests (Macrocystis pyrifera): Insights from a dynamically scaled laboratory model

Flume instrumentation for measurement of drag on flexible elements under waves

Seagrass blade motion under waves and its impact on wave decay

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