Two useful models include Bailard's (1981) energetics model, which 

 estimates sediment flux from measured wave and current data over the 

 surf zone, and Guza and Thornton's (1985a, b) model, which is concerned 

 with surf zone conditions where bed shear stresses and energy dissipation 

 are strongly dominated by waves. Equations of both models help to deter- 

 mine if the cross-shore component of the immersed weight sediment trans- 

 port within the surf zone is onshore or offshore. 



A laboratory model developed by Hattori and Kawamata (1980), and its 

 comparison with field data, is one approach which concerns the cross- 

 shore transport of sediment in the surf zone. This model is based on the 

 concept of the balance of power extended on sand grains generated by 

 breaking waves, the beach slope, and the effect of gravity. Hattori and 

 Kawamata theorized that cross-shore transport of sediment in the surf 

 zone is a function of the dimensionless fall-time parameter as described 

 by: 



C = 



( 



tanP 



W_ 



gT 



where: 



when 



C = a constant determined from laboratory and field data 



C < 0.5 onshore transport results - accretive profile 



= 0.5 no net transport results - equilibrium profile 



> 0.5 offshore transport results - erosive profile 



tan P = bottom slope in the surf zone 



W^ = fall velocity of a sand grain of diameter d^Q 



T= wave period 



H^ = deepwater significant wave height 



L^ = deepwater wavelength 



Hattori and Kawamata (1980) continue that net cross-shore transport in 

 the surf zone is a result of the stirring power P (which is a function of 

 submerged weight of sand grains, maximum wave-induced velocity, bot- 

 tom slope in the surf zone, water depth at the breaking position, and width 

 of the surf zone) and the resisting power P (which is a function of fall 

 velocity of a sand grain and the submerged weight of the sand grain. 

 When P^ > P^, sand grains keep in suspension due to breaking waves, and 



Chapter 3 Evidence of Cross-Shore Sediment Transport 



23 



