significant net offshore transport of sand." Bruun examined evidence for 

 the capability of offshore currents to transport sediment beyond the equi- 

 librium profile closure depth. He chose 18 m as a "reasonable assump- 

 tion" for this closure depth. He based this on the depth at which there is 

 no measurable (within the error bars of profile measurement) change in 

 pre- and post-storm inner shelf profiles. 



Hallermeier (1978, 1981a) presented a model to estimate the seaward 

 limit of sediment transport resulting from erosion (or offshore sediment 

 transport). He developed a simple predictive equation, based on labora- 

 tory studies, to estimate the annual depth of the seaward limit. He defined 

 two limits to an area he called the shoal zone (Figure 1). In the shoal 

 zone, "surface waves are likely to cause little sand transport; ...waves 

 have neither strong nor negligible effects on the sand bed" (Hallermeier 

 1981a). The seaward limit to the shoal zone (d.) is the depth limit to sedi- 

 ment motion initiation by normal waves. This implies that significant 

 onshore-offshore sediment transport is restricted to water depths less than 

 d. The offshore zone is seaward of the shoal zone and is characterized by 

 insignificant onshore-offshore transport by waves. 



The landward limit of the shoal zone (d^) separates the shoal zone and 

 the littoral zone. The littoral zone is characterized by significant long- 

 shore and onshore-offshore sediment transport due to increased bed stress 

 and sediment transport by breaking and near-breaking waves. According 

 to Hallermeier (1977), d^ can be described by a critical value of a sedi- 

 ment entrainment parameter (O ) in the form of a Froude number: 



^,= U^^/y'gd=0.03 (3) 



This critical value assumes that an intensely agitated bed usually exists 

 seaward of the surf zone. Hallermeier (1977) suggested an analytical 

 approximation, using linear wave theory for shoaling waves, to predict an 

 annual value of d^: 



di = 2.1^H^-6%.5{H]/gT]) 



where 



dj = annual depth of closure below mean low water 



H^ = nearshore nonbreaking wave height exceeding 12 hr/yr 



T = corresponding wave period 



g = acceleration due to gravity 



According to the above equation, d^ is primarily dependent on wave 

 height with an adjustment for wave steepness. 



Chapter 2 Inner Shelf Concepts 



