excellent agreement with new laboratory data. This was for both Hj-j^g and 

 n variations across plane and bar-trough profiles. Improvement in the 

 theory to match the data for low steepness waves is expected by incorpora- 

 tion of a wave breaking criteria over a range of wave heights with varying 

 probability (following Goda, 1975). 



Wave height variation across the surf zone and wave-induced setup are 

 obviously related. All experimental evidence indicates that as beach slope 

 decreases, the y ratio departs further from a constant value across the 

 surf zone. Distance from the breaker line is an important variable. A 

 constant y ratio in the surf zone is incorrect (eq. 33) for all beach 

 profiles. The surf zone energy dissipation model based upon equation (44) 

 with equation (124), i.e. 



dF 



> 



dF 



+ D = 



with 



D = i. Q^ f Pg H^ 



as developed by Battjes and Janssen (1976) is the most acceptable for all 

 beach profiles at this time. Local wave heights in the surf zone are 

 found by integrations so they logically depend upon all preceding sea- 

 ward water depths plus the local depth. It is recommended that Battjes' 

 model of the surf zone be studied further for regular wave setup and wave 

 height decay. Additional comparisons with experimental data plus some 

 minor modifications to the theory are also warranted. 



Wave setdown and setup theoretical equations for oblique wave inci- 

 dence (eqs. 39, 40, and 41) are not recommended. They. are based on 

 linear radiation stress theory, constant y in the surf zone, and neglect 

 the feedback of the longshore current induced on the wave motion. No 

 comparisons with experimental data have been attempted. 



b. Longshore Currents . If a rough estimate of the average long- 

 shore current is needed it is recommended that the expression 



V = K/ghT sin (2a^) K ~ 0.3-0.6 (170) 



b b 



be employed. Komar and Inman (1970) empirically obtained K ~ 0.6 for the 

 midsurf velocity vi^ from results of sand transport studies. Dette (1974) 

 obtained K ~ 0.3 from measurements in the North Sea and an analysis of all 

 formulas including those based upon radiation stresses for the average 

 current. Beach slope and bottom roughness do not appear in the empirically 

 determined equation (169) since it has been found theoretically that the 

 midsurf velocity is relatively insensitive to changes in these independent 

 variables (Kraus and Sasaki, 1979). 



224 



