Figure 13. Schematic of performance measures used in empirical analysis 



where V represents distance from the established basehne (subscripts 1-5 indicate 

 positions within the groin compartment for trapezoidal rule area calculation), and 

 / represents the length of groins for the respective compartments. 



Figure 14 is a plot of the groin spacing/length ratio of compartments 51 to 

 103 and the associated fill ratios. There is significant scatter in the data, attri- 

 buted to varying sediment supply (for example, because of local fill operations) 

 and gradients in the longshore sand transport rate. However, a distinct decreas- 

 ing trend in maximum fill ratio with increasing width-to-length ratio is evident. 

 Width-to- length ratios between 1 and 2 result in maximum fill ratios of approxi- 

 mately 40 percent, whereas width-to-length ratios greater than 3 result in fill 

 ratios on the order of 10-15 percent. Therefore, width-to-length ratios between 1 

 and 2 are recommended for this section of coast. 



Knowledge of the relative amount of fill that a particular groin compartment 

 may retain is helpful infonnation, but not the focus of functional design. The 

 design requirement for this study is the minimum dry beach width of the groin 

 compartments, as defined in Figure 13. Figure 15 presents minimum distance to 

 the baseline (seawall) versus width-length ratio for groin compartments 51-81. 

 Groin compartments south of Groin 83 were excluded from this analysis because 

 of the inconsistent nature of the groin field. The groin field south of Groin 83 is 

 characterized by mixed T-head and linear groins, landward set back of the sea- 

 wall, and portions of shoreline without seawalls. From Figure 15, width-to- 

 length ratios of 1 .5 provide a 75-ft dry beach, assuming a constructed groin field 

 will behave similarly to the existing groins. Groin compartments with minimum 

 berm widths greater than 75 ft are bounded by 300- to 400-ft structures. One 

 alternative presented by CP&E (1997) includes a groin field with 280-ft-long 



14 



Chapter 3 Functional Design 



