pending sediment. The effective turbulence of the flow is evidently not 

 affected by viscosity changes, but the fall velocity of sand in turbulent 

 water (nearly the same as the fall velocity in still water) is directly 

 related to viscosity. The temperature effect is greatest for particle 

 sizes between 0.25 and 0.5 millimeter and next greatest for the 0.125- 

 to 0.25-millimeter range, and the effect increased with increasing depth. 

 (The sediment used in the LEBS experiments had a dso of 0.22 to 0.23 

 millimeter.) (c) Changes in viscosity affected the fall velocity which 

 changed the dso of the bedload and thus the bed forms. (The size dis- 

 tribution of the SPTB sand was narrow, so this effect would be negligible.) 

 Changes in bed form change the resistance to flow and thus the sediment 

 discharge. Temperature effects in both directions were found; i.e., 

 sediment discharge both increased and decreased with increasing tempera- 

 ture. 



Taylor and Vanoni (1972a, 19 72b) examined temperature effects in both 

 low- and high-transport flows, and they also found temperature effects in 

 both directions in each case. 



For low-transport flow, Taylor and Vanoni found that the direction of 

 the effect was related to position on the Shields curve (Fig. 2.45 in 

 American Society of Civil Engineers, 1975; shear stress versus boundary 

 Reynolds number) where the Shields curve slopes down, increasing tempera- 

 ture caused increasing sediment discharge; where the Shields curve slopes 

 up, increasing temperature caused decreasing sediment discharge; and where 

 the Shields curve is flat, increasing temperature caused no change in 

 discharge. 



For high-transport flows, they found that the effect was related to 

 particle size: for the particles finer than 0.135 millimeter, suspended- 

 sediment concentrations at all depths increased with increasing tempera- 

 ture; for particles coarser than 0.135 millimeter, the concentrations at 

 all depths decreased with increasing temperature; but for particles with 

 a dso of 0.135 millimeter, concentrations at the higher elevations 

 increased with increasing temperature and at the lower elevations 

 decreased with increasing temperature. 



c. LEBS Results--Oscillatory Flow . Those results for unidirectional 

 flow point out the complexity of the temperature effect, so it is not un- 

 reasonable to expect a complex temperature-viscosity effect on sediment 

 transport in oscillatory flow. These experiments were obviously not 

 designed to study temperature effects since temperature was uncontrolled, 

 but they do indicate the potential for temperature effects. Temperature 

 changes are compared to the shoreline recession rate and volume erosion 

 rate in the discussions that follow. Because the backshore slope was 

 not flat the volume erosion and profile development rates were propor- 

 tional to the square of the shoreline recession rate in these tests. 



(1) 1.50-Second Wave . In experiment 72C-10 (Fig. 61) the shore- 

 line recession rate was decreasing, which means that the volume erosion 

 rate was decreasing or near constant, while the temperature was gradually 

 falling. 



Ill 



