Topics in Longshore Currents PDF Download
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Author: John Casey Church
Publisher:
ISBN:
Category : Littoral drift
Languages : en
Pages : 140
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Book Description
The momentum equation governing mean longshore currents on straight beaches is a balance of forcing from the momentum transfer of the oscillatory wave motion, turbulent momentum transfer (mixing), and bottom stress. Of these, the wave's contribution is well understood, but the remaining two are not, principally due to the complicated hydrodynamics of the surf-zone. Addressing the bottom stress term, a longshore current model is developed which includes a modification of the bottom stress due to the effects of breaking-wave induced turbulence. A one-dimensional turbulent kinetic energy equation is used to model this breaking-wave induced turbulence, producing a spatially varying bottom friction coefficient. The modeled longshore current cross-shore profiles show improved agreement with field observations. In a second bottom stress study, vertical profiles of mean longshore currents are examined using field data obtained with vertically stacked electromagnetic current meters with the goal of measuring the bottom stress and its associated drag coefficient. The profiles are observed to become vertically uniform whenever the ratio of wave height to depth exceeds 0.3, indicating that nearly all of the waves passing a given location are breaking. Finally, horizontal turbulent momentum transfer (mixing) is examined for the case of shear instabilities of the longshore current.
Author: John Casey Church
Publisher:
ISBN:
Category : Littoral drift
Languages : en
Pages : 140
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Book Description
The momentum equation governing mean longshore currents on straight beaches is a balance of forcing from the momentum transfer of the oscillatory wave motion, turbulent momentum transfer (mixing), and bottom stress. Of these, the wave's contribution is well understood, but the remaining two are not, principally due to the complicated hydrodynamics of the surf-zone. Addressing the bottom stress term, a longshore current model is developed which includes a modification of the bottom stress due to the effects of breaking-wave induced turbulence. A one-dimensional turbulent kinetic energy equation is used to model this breaking-wave induced turbulence, producing a spatially varying bottom friction coefficient. The modeled longshore current cross-shore profiles show improved agreement with field observations. In a second bottom stress study, vertical profiles of mean longshore currents are examined using field data obtained with vertically stacked electromagnetic current meters with the goal of measuring the bottom stress and its associated drag coefficient. The profiles are observed to become vertically uniform whenever the ratio of wave height to depth exceeds 0.3, indicating that nearly all of the waves passing a given location are breaking. Finally, horizontal turbulent momentum transfer (mixing) is examined for the case of shear instabilities of the longshore current.
Author: Cyril Jerome Galvin
Publisher:
ISBN:
Category : Littoral drift
Languages : en
Pages : 32
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Book Description
Author: Cyril Jerome Galvin
Publisher:
ISBN:
Category : Beaches
Languages : en
Pages : 96
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Book Description
Author: Dennis James Whitford
Publisher:
ISBN:
Category : Banks (Oceanography)
Languages : en
Pages : 238
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Book Description
Previous investigations of longshore currents have included simplifying assumptions and restriction (such as a planar beach, a steady and depth uniform flow, spatially-variant bed shear stress and turbulent momentum exchange, and the exclusion of surface wind stress. These assumptions are quantitatively investigated by calculating the relative importance of each term in the longshore momentum balance with an emphasis on the relative importance of wind forcing across the barred nearshore. Wind and wave forcing of longshore currents across a barred beach are examined using both a numerical model and field measurements. A local momentum balance was measured at various locations across the surf zone during the SUPERDUCK experiment held at the USACE CERC Field Research Facility, Duck, N.C. in October 1986. A moveable sled was instrumented with pressure, current, and wind sensors to measure the various terms in the longshore momentum equation. Stability-dependent atmospheric drag coefficients for the surf zone are determined from wind stress measurements acquired just beyond the surf zone and wind speed measurements acquired from an anemometer atop the 9 m sled mast. Breaking waves were visually identified and electronically marked on the data tapes. Keywords: Ocean currents; Air water interactions; Nearshore surf zone; Wind stress; Theses. (EDC).
Author: Cyril Jerome Galvin
Publisher:
ISBN:
Category : Ocean currents
Languages : en
Pages : 18
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Book Description
Author: Coastal Engineering Research Center (U.S.)
Publisher:
ISBN:
Category : Beach erosion
Languages : en
Pages : 1082
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Book Description
Author: Scott L. Douglass
Publisher: World Scientific
ISBN: 9789812776907
Category : Science
Languages : en
Pages : 114
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Book Description
This book tells you where beach sand comes from, how waves are formed and how they break and move sand down the coast, how OC works of manOCO have blocked this movement and caused beach erosion, and what can be done to save the beaches for future generations of Americans. A three-part prescription for healthy beaches is proposed: OC backing offOCO, OC bypassing sandOCO, and OC beach nourishmentOCO. So if you love waves and beaches, and care about the future of your favorite beach spot, then read this book while you enjoy the beach."
Author:
Publisher:
ISBN:
Category : Beach erosion
Languages : en
Pages : 232
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Book Description
Author: B. Johns
Publisher: Elsevier
ISBN: 0080870732
Category : Science
Languages : en
Pages : 483
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Book Description
This book provides a thorough treatment of both theoretical and observational aspects of the interaction between the sea-floor and the near-sea-floor dynamics; the effect this has on the distribution of internal and seabed stress; and the relevance of the associated dynamics to sedimentation processes. The theoretical work described involved both analytical and numerical modelling studies of a wide range of near-shore and shelf processes. These provide a valuable store of information on the interaction between the sea-floor and the dynamics of the overlying water. The book also includes an account of tidal analysis techniques and how these are being applied in the analysis of tidal current measurements. The observational studies relate to measurements of near-sea-floor turbulence and sand-transport in the littoral zone.
Author: Antonio Fernando Garcez Faria
Publisher:
ISBN:
Category : Ocean circulation
Languages : en
Pages : 52
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Book Description
The long shore current maximum observed in the trough of a barred beach during the nearshore dynamics experiment DELILAH at Duck, North Carolina, is not predicted by present theory. The simplest longshore curren models balance cross-shore changes in the alongshore wave momentum (radiation stress) with the alongshore bottom shear stress. Waves break over the bar, reform in the trough and again break on the foreshore resulting in changes in the radiation stress, which predicts two jets, one over the bar and the other at the foreshore, which does not agree with the observed current maximum in the trough. The advection of the momentum of the longshore current by mean cross-shore currents as a source of momentum mixing is investigated. The longshore current is strongest toward the surface and decreasing to zero at the bottom. The cross-shore mean current has an onshore transport in the wave crest/trough region and an offshore transport beneath (undertow). The net interaction can induce significant lateral mixing of the alongshore momentum of the mean currents, which is shown using a simplified three- dimension model of nearshore currents to explain much of the differences with observations.
