b. The base concentration, C, (eq. 9), for flume measurements 
is a function of the sediment charge in the flume and therefore could 
not be correlated to flow hydraulics. As shown by Einstein (1950), a 
flow is only capable of transporting a limited amount of sediment of a 
given size. This limiting capacity is determined by the flow velocity, 
sediment characteristics, and roughness of the boundary. In addition, 
the flow will only transport this capacity rate if there is a sufficient 
supply of sediment available. Otherwise, the transport rate will be 
reduced by the ratio of the supply rate to the capacity rate. Because 
the capacity transport rate for a given flow is determined by the proba- 
bility of a particular sediment particle being subjected to sufficient 
hydraulic forces to move it, there must be some particles in the bed that 
are not in motion at any instant of time. Had there been enough sediment 
in the flume to satisfy the flow's sediment transport capacity, the 
measured Co, could have been correlated to flow velocity. Unfortunately, 
under those conditions some sediment must be loosely deposited on the 
flume bed, thereby changing the fixed-bed geometry and roughness. There- 
fore, only the flow's capacity to transport sediment of a specific size 
can be estimated. This estimate must use the capacity base concentration 
calculated from Kalkanis' (1964) bedload equation and not the base concen- 
trations measured in this investigation. 
canines thesrangerotetiliow velocities W0.2foot per second i<sU-¥< il 
feet per second, for amplitudes of oscillation equal to or greater than 
0.693 foot, and for V, = 0.035 foot per second, the slope of the exponen- 
tial distribution of sediment concentration is a function of flow veloc- 
ity only. The slope, M, can be approximated from the flow velocity, 
U>, by equation (11). This equation is only a best fit empirical rela- 
tionship and cannot give reasonable approximations of M for Ug values 
very far outside the stated range. This becomes apparent when substitut- 
ing iniarlarge-valuevof WU, 330 exe, 2.0lneet per second, andjicaleulating 
M. The result would be a positive value for M; i.e., the concentration 
of sediment increases with elevation which is not reasonable. The limit- 
ing value of M for extremely large values of U, should be zero, or 
uniform concentration of sediment throughout the depth. At the other 
extreme, equation (11) gives a value of M = -18.45 feet! for Uz = 0 foot 
per second which is also not reasonable. But, for low values of U,, any 
continuous function is not expected to give a correct relationship since 
at some point the flow changes from turbulent to laminar. In laminar 
flow there is no turbulence and therefore no sediment suspension. As Up 
is increased, the flow, at some velocity, suddenly changes from laminar 
to turbulent and just as suddenly the suspended-sediment concentration 
changes from zero to some positive value. Therefore, the relationship 
expressed by equation (11) becomes invalid at some small value of U)- 
d. For the flow velocities studied, the sediment-settling velocity 
has a significant effect on the slope of the concentration distribution 
curve. Not enough data were obtained to define the relationship between 
V, and M, but the data did yield the qualitative relationship that for 
constant U,, M decreases (or becomes a larger negative value) with in- 
creasing Vs. As discussed earlier, if the sediment exchange coefficient 
43 
