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|Title:||Surf zone currents, volume 1: state of knowledge|
|Authors:||Texas A&M University, Dept. of Civil Engineering|
Basco, David R.
Surf Zone Currents
|Publisher:||Coastal Engineering Research Center (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Miscellaneous report (Coastal Engineering Research Center (U.S.)) ; no. 82-7 v.1.|
Abstract: Investigations of surf zone currents have been conducted world wide for more than 60 years. The primary motivation has been to improve methods of understanding sediment and coastal pollution processes. This report (Vol. I) and a companion report entitled, Annotated Bibliography of Surf Zone Currents (Vol. II) are part of a major new study of coastal currents initiated by the Coastal Engineering Research Center in 1979. The two reports provide a state-of-the-art summary of theories and experiments investigated since 1967. The theories before 1967 have been included in previous summaries (e.g., Galvin, 1967) Currents generated by short-period surface gravity waves both within and just beyond the breakers are of particular concern. The major types are longshore currents, nearshore circulations, rip currents, and wind-driven currents. Tidal currents are excluded. The study included the review of physical processes, theories, field and laboratory experirnents , numerical models, and the measurement technology and instruments used to conduct the experiments. Related topics included are wave thrust (radiation stress) principles, wave setdown and setup, boundary and lateral mixing stress models, edge waves, wave breaking, and surf zone energy dissipation. There are currently two major theoretical approaches to coastal hydrodynamics, each in a different stage of development. Both approaches assume uniform currents with depth, require numerical computer methods for general solutions, and both suffer from a limited data base for verification. The older, time-averaged radiation stress theory is in the final refinement stage and is now generally accepted. The new Boussinesq theory, which is just being implemented, follows the instantaneous water surface and current variations to essentially go beyond the time-averaged mean to observe the physics occuring within each wave period. The drawbacks and limitations of both approaches are different. The radiation stress approach requires a priori specification of wave height fields by seperate means and closure coefficients obtained from time-averaged field data. The proper averaging time is unknown. A major limitation of the Boussinesq theory is the size and speed of computers needed to handle the vast grids and large number of time steps required for a meaningful simulation. Both methods rely on wave breaking and surf zone empiricism that needs considerable improvement. Detailed state-of-the-art summaries are presented for both methods. For practical applications in coastal engineering it is concluded that the knowledge gained from future research with the Boussinesq method will best serve to improve the time-averaged radiation stress approach and and its eventual coupling to coastal sediment and pollutant transport simulations.
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|Appears in Collections:||Miscellaneous Report|