Influence of K 



444. The empirical transport rate coefficient K (Equation 33) primar- 

 ily governs the time response of the beach profile. A smaller value gives a 

 longer elapsed time before equilibrium is attained, whereas a larger value 

 produces more rapid evolution. However, K also influences equilibrium bar 

 volume, as seen in Equation 36. Although Equation 36 was derived assuming 

 uniform energy dissipation per unit volume everywhere in the surf zone and not 

 just in zones of fully broken waves, it gives important qualitative informa- 

 tion about the influence of K and € . A smaller K-value implies a flatter 

 equilibrium beach profile with correspondingly more sand to be moved from the 

 inshore for a fixed initial profile slope before equilibrium is attained. 



445. Figure 61 illustrates the growth of bar volume with time for 

 different values of the transport rate coefficient. For K = 2.2 10"^ m''/N, 

 more than 90 percent of the equilibrium bar volume was reached after 20 hr, 

 whereas for K = 0.4 10"^ m^/N only approximately 30 percent of the final bar 

 volume was reached. The dependence of equilibrium bar volume on K is 

 introduced through the slope term in the transport equation. Without this 

 term the shape of the equilibrium beach profile would be independent of K , 

 and this coefficient would only influence the time response of the profile. 



446. Calculated maximum bar height (defined with respect to the initial 

 plane beach profile) as a function of time is shown in Figure 62 for various 

 K-values. Maximum equilibrium bar height was insensitive to the value of K . 

 However, as expected, time evolution of the bar height is controlled by K , 

 showing a more rapid change for larger values. The location of the mass 

 center of the bar was only slightly influenced by the value of K , with the 

 mass center somewhat displaced shoreward when the value of K was decreased. 

 Influence of e 



447. The empirical coefficient e in the slope term in Equation 33 

 mainly influences equilibrium bar volume and thus the amount of sand that is 

 redistributed along the profile to reach equilibrium. Profile response was 

 similar for quite different values of e during the initial phase of the 

 simulation and differed only after longer elapsed times (Figure 63). Equation 

 36 indicates that a smaller e -value implies a steeper equilibrium beach 

 profile and less sand to be moved before a state of equilibrium occurs. The 

 effect of the slope term on maximum bar height was weak, where a change in 



184 



