and an arbitrary sloping bottom. In the energetics stream approach, it is 

 assumed that the rate of sediment transport is proportional to the rate of 

 energy dissipation of the "stream," which for the coastal case is the energy 

 loss caused by the decay of broken waves and by bottom friction. 



60. Bailard's formula is an algebraic expression consisting of two 

 terms intended to describe transport contributions from bed load and 

 suspended load. Empirical efficiency factors enter for both bed and 

 suspended load; these factors express the capability of the stream to move 

 the sediment. The transport equation also contains the sediment fall 

 velocity (in the suspended load term), the local beach slope, the internal 

 angle of friction of the sediment (for bed load), and higher moments of the 

 wave orbital velocity. (In the general case in which longshore transport is 

 included, the equation contains longshore components of the steady and 

 unsteady wave and wave-induced currents.) The wave height and period enter 

 through the wave orbital velocities. 



61. Bailard (1982, 1983), who applied his transport equation to 

 calculate profile change observed in the field, reported disappointing 

 results, finding that the model accounted for only 19 percent of the observed 

 variance in the measured beach volume change. He noted that actual beach 

 profile change is difficult to calculate directly from sediment transport 

 rates because the net transport is a small difference resulting from two 

 large (onshore and offshore) transport rates. The required moments of the 

 wave orbital velocity cannot presently be calculated from existing wave 

 theory with any confidence. In fact, the orbital velocities of commonly used 

 small amplitude theory are symmetric and would yield no net transport at a 

 given location. A wave theory suitable for describing surf zone waves has 

 not yet been developed. Bailard used empirical moment estimates obtained 

 from current meter records. These instruments and records may not be 

 sufficiently accurate for the intended purpose (Aubrey and Trowbridge 1985). 



62. In summary, the transport equation of Bailard is relatively 

 sophisticated and ambitious in describing many of the physical processes, but 

 its applicability has not been demonstrated. In addition, despite its 

 sophistication, the sediment transport equation still relies on empirical 

 parameters (efficiencies, moments, and friction factor), and requires know- 

 ledge of quantities which are difficult to calculate. As with the other 

 models introduced above, the onshore boundary condition has not been 



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