effect, since this effect was not seen for this wavelength in the wider 

 tank. Lateral variations in the position of contours in the inner off- 

 shore are shown in Figure 58. 



Lateral variations at the toe of the profile are shown in Figure 59, 

 which compares the movement of selected contours, and in Figure 60, which 

 is a contour map of the final profile. 



4. Water Temperature Effects . 



a. Processes. Since the 10 LEBS experiments were conducted in an 

 outdoor basin, water temperature was an uncontrolled variable, varying 

 from 4° to 31° Celsius, the dynamic viscosity varying from 3.30 x 10" 5 

 to 1.64 x 10" 5 pounds-second per square foot (1.61 x 10~ 5 to 0.80 x 10~ 5 

 grams-second per square centimeter) (Daily and Harleman, 1966). Vis- 

 cosity is known to affect the fall velocity of sediment particles in 

 settling tubes: as the viscosity of water increases, the fall velocity 

 decreases (see Fig. 4-31 in U.S. Army, Corps of Engineers, Coastal Engi- 

 neering Research Center, 1977) . Since viscosity has been shown to have 

 several effects on sediment transport in unidirectional flow (American 

 Society of Civil Engineers, 1975), it is likely that water temperature 

 and viscosity would affect sediment suspension and transport in oscilla- 

 tory flow. For example, the erosion of beaches in the winter months may 

 not be the result of increased wave steepness alone, but perhaps due to 

 the decrease in water temperature as well. 



A greater knowledge of temperature-viscosity effects on sediment 

 transport in oscillatory flow is needed for at least three purposes: 

 (a) to understand the effects of temperature on erosion and accretion 

 in nature, (b) to understand the scale effects in the laboratory when 

 relating laboratory results obtained with one temperature history to 

 prototype localities with another temperature history, and (c) to under- 

 stand the laboratory effects when attempting to compare results from a 

 series of research experiments with one another when the water tempera- 

 ture was not controlled. The lack of knowledge on this last point has 

 made it difficult to prove that the lack of profile equilibrium in 

 several of these experiments was not due to a constantly decreasing 

 water temperature. 



The important effects of temperature-viscosity on sediment transport in 

 unidirectional flow and the results on the effect of temperature-viscosity 

 on shoreline recession and profile development in the LEBS experiments are 

 discussed below. 



b. Literature Review—Unidirectional Flow . Colby and Scott (1965) 

 found three effects of water temperature on sediment discharge: (a) Vis- 

 cosity changes cause changes in the thickness of the laminar sublayer 

 which affect the relationship between mean velocity and effective bed 

 shear. (b) The vertical distribution of suspended sediment depends on 

 the ratio between the fall velocity of sediment particles in a turbulent 

 sediment-water mixture and the effective turbulence of the flow for sus- 



107 



