As in Kalkanis' bedload function, the approach to the suspended 
load is based on many of the same principles proposed by Einstein (1950) 
in his theory of bedload and suspended-load transport in unidirectional 
flow. Analysis of suspended load in oscillating flow is more complicated 
than that of unidirectional flow because of two factors. First, in uni- 
directional open channel flow the entire depth of flow is turbulent and 
the relatively high turbulent velocity fluctuations allow the sediment 
exchange coefficient to be approximated by the momentum exchange coeffi- 
cient which can be obtained from the shear-stress distribution. In 
oscillatory flow this is not possible. Both laboratory and field obser- 
vations indicate that suspension of sediment occurs to depths considerably 
above the boundary layer in an area where the shear stresses due to the 
oscillating motion are extremely small and difficult to measure. Although 
it may be possible to express a sediment exchange coefficient in the 
boundary layer as a function of the mean shear stress, this would not 
provide a means of estimating the sediment exchange coefficient above 
the boundary layer. Therefore, a sediment exchange coefficient which is 
not based on a shear-stress distribution must be found. 
The second factor concerns the magnitude of the turbulent velocity 
fluctuations. Offshore of the breaker zone where the flow velocities 
near the bed are low, only a small part of the wave energy is dissipated 
by friction at the boundary. The remaining wave energy is lost inshore 
by the breaking waves. Because of the relatively low intensity of tur- 
bulence in this offshore area, the vertical velocity fluctuations are of 
the same order of magnitude as the settling velocity of the sediment. 
Under these conditions, the sediment exchange coefficient is highly 
dependent on the sediment--settling velocity. Therefore, measured dis- 
tributions of turbulent velocity fluctuations and sediment concentrations 
must be used in analyzing the upward turbulent flux and downward turbulent 
and gravitational flux for each sediment-settling velocity. 
To obtain a relationship between sediment suspension and flow hydrau- 
lics in an oscillating flow, concentration distributions for various flow 
conditions must be measured. The sediment exchange coefficient is deter- 
mined from these measurements. Next, the turbulent velocity fluctuation 
distribution with time at a constant elevation and its distribution with 
elevation must be measured. This measurement will yield the information 
necessary to describe the fluid exchange. The distribution with eleva- 
tion will yield a velocity scale, one of the two variables composing the 
sediment exchange coefficient. From the sediment exchange coefficient 
and the velocity scale, the second variable (the length scale or its 
associated time scale) can be calculated. Knowledge of these fundamental 
variables of suspension as a function of the flow hydraulics should lead 
to a practical method of estimating the suspended-load distribution, and 
indicate the important variables of suspension in an oscillating flow. 
The only other requirement for a solution to the suspended load is a 
knowledge of a base concentration as a function of flow hydraulics. The 
base concentration is determined from Kalkanis' (1964) bedload theory, 
being the concentration at the top of the bedload layer. 
