5. Net Transport of Sediment in the Ocean. 
The initiation of sediment movement in the ocean is by wave action. 
Since the waves are approximately linear, the wave-induced fluid motion 
is a symmetric oscillation causing an equally symmetric movement of the 
sediment. This motion ordinarily cannot cause net transport of sediment, 
but it does suspend sediment so that currents superimposed on the oscil- 
lating velocity will cause a net transport of the sediment. Examples of 
unidirectional currents in the ocean are the longshore current caused by 
waves attacking the coastline at an acute angle and the secondary currents 
caused by the coastline geometry. These two examples indicate that deter- 
mination of the transporting current shouid be by field measurement. 
6. Additional Investigations Needed to Complete the Suspension Theory. 
The suspended-load theory is by no means complete. The relationship 
between the rate of decay of sediment concentration, M, and sediment- 
settling velocity, Vs, is needed. Figure 15 indicates that settling 
velocity has a significant affect on the distribution of sediment con- 
centration, but there are not enough data to indicate the relationship. 
Additional measurements are required to quantitatively determine the 
relationship between M and V, for a constant Up. 
Another variable affecting the suspended-load theory and not studied 
in this investigation is the bed roughness. It is probable that a change 
in bed roughness would affect the intensity of turbulence at a given 
elevation. Also, as discussed in Section II, the amplitude of oscilla- 
tion relative to the wavelength of the bed roughness has an affect on the 
distribution of suspended sediment. Determination of how the bed rough- 
ness affects sediment suspension requires a great deal of experimentation; 
however, the results of this investigation will supply some guidelines 
which would reduce the amount of experimental work required. 
7. Conclusions. 
These experiments in an oscillating flow simulating wave motion at 
the ocean floor provide results which, in some cases, substantiate pre- 
vious results and provide new information on the behavior of sediment 
suspension. It should be stressed that the conclusions of this investi- 
gation are confined to the rather limited range of the variables studied. 
The conclusions obtained from sediment concentration measurements are: 
a. The relationship between the mean sediment concentration and 
elevation above the bed is exponential. This conclusion is based on 65 
concentration distribution relationships covering a wide range of proto- 
type flow conditions and each composed of numerous point concentration 
measurements. Typical examples of this relationship are shown in Figure 
5 and the basic data substantiating this conclusion are given in the 
appendix. Although this relationship was determined using an artificial 
TI 
