directly in this investigation and is given by equation (22). The sedi- 
ment exchange coefficient which is the product of the length and velocity 
scales was also measured directly and is given by equation (13). From 
these two equations, the corresponding length scale can be calculated as: 
ale =H GV Mesyy) extn (An Yo) (37) 
For the limited flow conditions investigated, all the variables of 
equations (13), (22), and (37) have been found as a function of U,, 
where U, is a function of the surface wavelength, period, and water 
depth. The variable A was found to be a constant (= -10.57 feet-!), 
and M and s, are graphically given in Figures 6 and 27, respectively. 
These expressions for the velocity and length scales are physically 
reasonable. Not only is the base turbulent velocity a function of the 
surface wave intensity (Fig. 27), but the exchange length tends to small 
values as the ocean bed is approached, indicating that no sediment should 
be exchanged across the bed surface. 
4. The Base Concentration, C,. 
With the exception of the base concentration, C,, all the variables 
needed to describe the suspended load as a function of flow hydraulics 
have been discussed. The following is only a brief discussion of the 
base concentration. Kalkanis (1964) provides a complete mathematical 
derivation. 
In oscillating flow, as in unidirectional flow, sediment transport 
is by two different types: (a) Bedload transport, and (b) suspended-load 
transport. As discussed in Section I, the thickness of the bedload layer 
is about two-grain diameters. Therefore, for both prototype and experi- 
mental sediments, the bedload is contained in the boundary layer described 
in Section II. The theory proposed by Kalkanis to predict the amount of 
bedload transport and the concentration of sediment is general and only 
requires knowledge of the surface wave characteristics, the water depth, 
the bed sediment characteristics, and statistical parameters which have 
been found experimentally. Because the thickness of the bedload layer 
is small, the concentration of sediment in this layer is assumed constant 
and equal to Cy. The concentration, Co, for the bedload is the base 
concentration to be used for the suspended load. 
Using Co as the suspended-load concentration incorporates a small 
error in the total suspended load. As indicated previously, the bedload 
is contained in the boundary layer. The distribution of sediment concen- 
tration in this area is unknown. Because the distance between the top of 
the boundary layer and the top of the bed layer is small, extension of 
the exponential suspension distribution down to the bed layer would incur 
only a minor error in the total amount of sediment in motion. 
70 
