(8) Different lateral mixing stress models should be employed 

 within and outside the breakers. Further research is needed to determine 

 which are most accurate. 



(9) No recommendations for state-of-the-art closure coefficients 

 are made. Continued indirect and direct determination from field data is 

 required. Bed friction factors must be correlated with relative boundary 

 roughness. Eddy viscosity closure coefficients should be related to surf 

 zone, Reynolds and Iribarren numbers. 



(10) Wind-induced longshore currents can be created in some 

 numerical models but have yet to be studied in detail. 



d. Nearshore Circulations . 



(1) All theory is based on the assumption (not verified) that 

 the two horizontal motions dominate the flows present nearshore. No three- 

 dimensional theory or models have been attempted. 



(2) The two-dimensional, conservation form equations of motion 

 including all acceleration, pressure and stress gradient terms should be 

 employed. Additional interaction terms discussed by Harris and Bodine (1978) 

 are incorporated indirectly by the closure coefficients. 



(3) None of the existing two-dimensional models are recommended 

 for engineering use. All exhibit serious limitations due to neglect of im- 

 portant terms or excessive numerical inaccuracies. Additional comprehensive 

 two-dimensional numerical modeling efforts are desirable. 



(4) Specification of wave height fields by linear wave theory 

 (shoaling, Snell's Law, diffraction theory) is questionable. Existing 

 numerical schemes for this purpose should be revised to incorporate nonlinear 

 (cnoidal) theory. 



(5) Numerical simulation of circulations, gyres, eddies, etc. in 

 free-surface flows is still an active research area in computational hy- 

 draulics. The eddy viscosity model is only one of many new turbulence closure 

 models being investigated. 



(6) No single theory is valid and verified to predict rip current 

 spacing. Semiempirical engineering estimates are available. While many 

 plausible mechanisms exist to trigger rip currents, bathymetry usually con- 

 trols their location. 



(7) Radiation stress principles can be employed to study vertical 

 circulations about a horizontal axis. No such studies were found in the 

 literature. 



3. Boussinesq Theory , 

 a. General . 



(1) The complete and correct form of the equations of motion for 

 variable bathymetry applications have yet to be finalized. Limited appli- 

 cations to date have been for gradually varying bathymetry. 



(2) Higher order accuracy numerical methods are required for a 

 solution and are still in the development stage. 



(3) Considerable research and development remains for applica- 

 tion to surf zone hydrodynamics. 



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