additional parameter to be added is cl>, the particle fall velocity, in feet per 

 second. For suspended sediment transport, particles in suspension fall by 

 gravity to the bed, where they subsequently are returned to the flow by 

 turbulence and transported by currents. During "equilibrium" or non-eroding 

 conditions, the amount of sediment falling into an area is equal to the amount 

 being carried out of the area. A conservation of mass equation can be written 

 for a given horizontal area of bed such that 



cj C E + e dCjdz = (29) 



where 



C s = sediment concentration in the water, lbj^/ft 3 



e = diffusion coefficient 



z = distance above bed, ft 

 Equation 29 is the basic differential equation for suspended sediment trans- 

 port and can be solved for certain cases if appropriate assumptions are used. 



16. Lane and Kalinske (1941) used the assumptions that the diffusion 

 coefficient is constant through the vertical section and equal to the average 

 value determined in terms of the von Karman constant and previously defined 

 shear velocity u* . Their solution for Equation 29 is given below: 



CjC k = [(h/z -D/Uz/A - i)f /0 - 4u - (30) 



where C A is a known concentration (in units consistent with C s ) at height A, 



in ft above the bed, and h is depth of flow, in feet. This equation has been 

 shown to produce relatively accurate results, but is applicable only for 

 equilibrium conditions for a known sediment size. 



Suspended-Load Transport in Oscillatory Flows 



17. Unlike unidirectional flows, analysis of suspended transport by 

 oscillatory flows is quite complex. Periodic turbulence- induced variations in 

 the direction and velocity of the water particles result in a non-homogeneous 

 region of water/sediment above the bottom. Due to the complexity of this 

 problem, research efforts primarily have resulted in empirical relationships 

 that attempt to relate wave characteristics (height and period), water depth, 

 sediment characteristics, and bottom roughness. Based on laboratory flume 

 studies, MacDonald (1973) found that concentration distribution C s (lb/ft 3 ) in 

 an oscillating flow could be estimated by 



20 



