11. DALRYMPLE, R.A., and LOZANO, C.J., "Wave-Current Interaction Models 

 for Rip Currents," Journal of Geophysical Research, Vol. 83, No. 

 C12, Dec. 1978, pp. 6063-6071. 



Keywords. Currents, Nearshore; Currents, Rip; Currents, Wave-Induced; 

 Shallow Water; Theory. 



Discussion. The shallow -water equations used by Longuet-Higgins (1970) 

 to discuss longshore currents are used to extend the work of LeBlond and 

 Tang (1974) in attempting to relate the spacing of rip currents to beach 

 and incident wave properties. The bottom is supposed to be flat 

 offshore of the breaker point and to be of uniform slope in the surf 

 zone. The equations are solved for a zero-order solution in which there 

 is no longshore variation. The full equations are then linearized about 

 this solution. 



Firstly, it is shown that an assumption of very slight refraction 

 (i.e., variations in wave direction assumed negligible) leads to no 

 periodic solution. An assumption of sinusoidal longshore variation, 

 which is reasonable for these linear equations, leads to a system of 

 ordinary differential equations for which solutions exist and are found 

 numerically. A significant numerical error in LeBlond and Tang (1974) 

 is noted. 



Coastal Eng Ineer ing Signif icance . This paper displays how far 

 away a satisfactory theory is for the details of rip currents, i.e., 

 properties such as their source and spacing. General qualitative con- 

 cepts of their generation have yet to be translated into really success- 

 ful theoretical models. 



12. EVANS, D.V., "The Transmission of Deep-Water Waves Across a Vortex 

 Sheet," Journal of Fluid Mechanics, Cambridge, England, Vol. 68, 

 No. 2, Mar. 1975, pp. 389-401. 



Keywords. Currents, Small-Scale; Shear Layer; Theory; Wave Reflection; 

 Wave Transmission. 



Discussion. The interaction of waves with shear currents which have a 

 length scale of variation much less than a wavelength is modeled in this 

 paper. The region of shear is assumed to be sufficiently narrow that it 

 is modeled by a vertical vortex sheet. The waves are of small amplitude 

 and obliquely incident to the vortex sheet. 



The mathematical problem is linearized and possible instabilities 

 of the vortex sheet are excluded from the analysis. An approximate 

 method of solution, which is accurate in other examples where results 

 can be checked, is used to find values for reflection and transmission 



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