Long Shore Currents and Wave Statistics in the Surf Zone PDF Download
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Author: J. Ian Collins
Publisher:
ISBN:
Category : Bathing beaches
Languages : en
Pages : 136
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Book Description
The report investigates some of the physical aspects of the surf zone with random seas. The statistics of wave height distributions are investigated for the surf zone over gentle sloping beaches. Longshore currents and wave set-up due to random seas are computed and compared with results for periodic waves. The mathematical stability of steady longshore currents on plane beaches is investigated and it is found that such solutions are unstable. (Author).
Author: J. Ian Collins
Publisher:
ISBN:
Category : Bathing beaches
Languages : en
Pages : 136
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Book Description
The report investigates some of the physical aspects of the surf zone with random seas. The statistics of wave height distributions are investigated for the surf zone over gentle sloping beaches. Longshore currents and wave set-up due to random seas are computed and compared with results for periodic waves. The mathematical stability of steady longshore currents on plane beaches is investigated and it is found that such solutions are unstable. (Author).
Author: James Ian Collins
Publisher:
ISBN:
Category : Sediment transport
Languages : en
Pages : 134
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Book Description
Author: James H. Balsillie
Publisher:
ISBN:
Category : Littoral drift
Languages : en
Pages : 0
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Book Description
Simultaneous field observations of breaker and current behavior have been made using techniques of the Littoral Environment Observation (LEO) program. This program, developed at CERC, is used to collect data on beach and surf conditions. The data base for this report represents a concentrated data collection effort over a period of 1 year at three beach sites at Point Mugu, California. Longshore current behavior is investigated in two ways: (a) Observed; and (b) predicted, using LEO data. Observed longshore currents are represented by the behavior of dye injected into the surf between the shoreline and breakers. Predicted longshore currents, based on the observation that longshore currents are generated primarily by waves, are estimated using a relationship for the average longshore current across the surf. The prediction model relies upon consideration of the radiation stress or wave thrust on water inside the breakers, and is evaluated using LEO breaker heights, angles of wave approach at breaking, and estimated widths of the surf zone. The degree of similarity between observed and predicted longshore currents is significantly high. This similarity not only suggests that the relationship for prediction of longshore currents is reasonable in field situtations, but that there is a surprising degree of internal consistency within typical LEO data sets.
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: Edward K. Noda
Publisher:
ISBN:
Category : Hydrodynamics
Languages : en
Pages : 258
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Book Description
The report presents a theoretical analysis on the generation and stabilization of nearshore, wave-induced circulation and longshore current patterns produced by the interaction of the incoming waves and local bottom topography. This interaction results in a spacial variation of wave characteristics which produces the driving mechanism for nearshore circulation patterns. Both normal and oblique wave incidence are considered with the imposed beach profiles developed from an examination of prototype data. The analytical model results are compared to field measurements and yield optimistic results. (Author).
Author: D. W. Ostendorf
Publisher:
ISBN:
Category : Littoral drift
Languages : en
Pages : 200
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Book Description
Author: Choule J. Sonu
Publisher:
ISBN:
Category : Wave-motion, Theory of
Languages : en
Pages : 152
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Book Description
For the purpose of aiding in the strategic planning of naval inshore warfare operations, a study has been performed to develop prediction technology for shallow water waves, breakers, and longshore current velocities, using the visually observed deep water wave statistics as input. Computer programs, code-named 'BREAKM' and 'STATBR, ' and various nomographs have been developed to permit predictions for both physical magnitude and long-term statistics. Information display formats have been developed with a view to permitting speedy review of various key physical parameters and comparison between adjacent regions. Predicted results compare reasonably well with visually observed nearshore data, provided that a tolerable amount of discrepancy exists due partly to local conditions not accounted for in our prediction, partly to the built-in safety margin in our prediction, and partly to the limitations inherent to the state of the art. (Author).
Author: Saad Mesbah M. Abdelrahman
Publisher:
ISBN:
Category : Beach erosion
Languages : en
Pages : 180
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Book Description
Water waves are one of the principal causes of shoreline changes. When waves break along the shore, they release their energy and momentum and give rise to a longshore current. The longshore current, along with the stirring action of the waves, is the primary mechanism for longshore sediment transport. The longshore sand transport rate is an essential factor determining erosion or accretion along a coast. If the longshore sand transport rate can be accurately estimated, a quantitative picture of shoreline evolution can be evaluated, including changes of the shoreline due to marine structures. In the present study, analytical and numerical models are developed based on a longshore current model for random waves and a sediment transport formulation by Thornton to predict the cross-shore sediment transport distribution and to compute the total volume of sand transport rate. The model is compared with the field data acquired from Leadbetter Beach, Santa Barbara, California.
Author: Cyril Jerome Galvin
Publisher:
ISBN:
Category : Ocean currents
Languages : en
Pages : 18
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Book Description
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.
