through time, together with a solid line showing the least-squares estimate of 

 the exponential decay. The coefficient of determination in this case was 

 92 percent. The difference between averaging the individual estimates of the 

 spatial decay coefficient and obtaining an overall estimate by using normaliz- 

 ed transport rates was small . 



345. The average spatial decay coefficient for erosional cases was 

 calculated for each case and related to wave properties and sand characteris- 

 tics. The overall average value of the decay coefficient was 0.18 m"^ with a 

 standard deviation of 0.06 m'^. Values ranged from a minimum of 0.12 m~^ to a 

 maximum of . 34 m" . 



346. Correlation analysis showed an inverse dependence of the spatial 

 decay coefficient on the breaking wave height and a direct dependence on the 

 grain size (correlation coefficients of -0.70 and 0.75, respectively). In 

 principle, a larger breaking wave height, for a specific grain size, would 

 stir up more sand and thus allow more of the entrained grains to disperse 

 seaward from the break point implying a more gradual decay in the transport 

 rate. For constant breaking wave height, larger sand grains are less likely 

 to be put into suspension and the transport rate distribution decays more 

 rapidly seaward of the break point. This intuitive picture is supported by 

 the correlation analysis. 



347. The spatial decay coefficient showed only a weak inverse depend- 

 ence on the wave period, giving a small correlation coefficient. Regression 

 between the decay coefficient and the breaking wave height and the grain 

 size explained 70 percent of the variation in the data. The regression 

 equation is 



A = 0.40 



(22) 



In Equation 22 the units of D are millimeters and the units of Hj, are 

 meters . 



348. Figure 46 illustrates decay coefficients calculated from the data 

 compared with values predicted by Equation 22. Note in Figure 46 that one of 

 the points influences the regression and correlation analysis considerably. 



142 



