coring conducted to water depths of about 35 meters. Between the major bio- 

 turbation in the offshore zone and the very limited bioturbation in the shore- 

 face zone, a transition zone occurs with almost all of the characteristics of 

 the flanking zones. Some uncertainty remains about seasonal wave effects at 

 the high-energy site because all sampling was conducted in the summer. 



(2) A Wave-Based Profile Zonation . Statistics of annual wave climate 

 together with sand characteristics for a certain site can be used to locate a 

 subaqueous buffer zone where expected waves should have neither strong nor 

 negligible effects on the sand bottom during a typical year (Hallermeier , 

 1981b). This calculated profile zonation is based on general aspects of sand 

 agitation by waves and is consistent with the limited available evidence on 

 onshore-offshore sand movements at specific sites. The site description used 

 for a calculation consists of the following: (a) the material characteristics 

 (y /y) and (subaqueous) dcQ and (b) the median annual significant wave 

 height H 5Q , the annual standard deviation of_signif icant wave height a, 

 and the annual average significant wave period T 



H 



The usually smaller water depth is a seaward limit to extreme surf-related 

 effects throughout a typical year. This water depth d is calculated from 



[' 



max 



(-d) 



50.137 



0.03^- 



1 8 d, 



0.5 



(4-25) 



where the numerical subscript indicates the peak near-bottom velocity that is 



exceeded 12 hours per year (0.137 percent occurrence level). For quartz sand 



in seawater and small-amplitude wave theory, equation (4-25) has the approxi- 

 mate solution 



s50 



12 a 



H 



(4-26) 



so that 



is roughly twice the extreme nearshore wave height exceeded 12 



hours per year. This calculated water depth shows agreement with available 

 data on the seaward limit to intense onshore-offshore sand transport, as 

 revealed by the closeout (to within ± 0.5 foot or ± 0.15 meter) of appreciable 

 seasonal excursions in profile elevations. Consideration of this moderately 

 rare wave condition seems consistent with general guidance on the most 

 effective events in geomorphic processes (Wolman and Miller, 1960). 



The other water depth is a seaward limit to sand agitation by the median 

 annual wave condition. This water depth d . is calculated from 



max. 



i-d) 



s50 



Mr -W^So 



°*^ (4-27) 



according to small-amplitude wave 



through the depth dependence in u 



theory. For quartz sand in seawater, the approximate solution to equation (4- 

 26) is 



0.5 



s50 s 



S_ 



5000 d 



50 



(4-28) 



4-73 



