distance from the original shoreline. 

 Nir (1982) 



15. Based on project performance of 12 breakwaters on the Israeli 

 coast, Nir (1982) concluded that accretion is very low or does not occur at 

 all if the segment length to offshore distance ratio has a value of 0.5 or 

 less : 



— - s 0.5 nondepositional condition (2) 



Assuming that the planform of the tombolo/salient formed a trapezoid, Nir 

 calculated the area and volume of each spit out to the depth of structure. 

 Dividing the volume by the area, Nir calculated the average sand thickness in 

 the tombolo/salient z^ and related it to the structure-distance ratio as 

 follows (note that the equation is dimensionally inconsistent) : 



z, (m) = 1.786 - 0.809 [—1 (3) 



The relationship was developed from prototype data with X/L^ values ranging 

 from 0.38 to 2.0, resulting in sand thicknesses ranging from approximately 0.3 

 to 1.7 m. Seven out of the twelve structures developed tombolos. Beach 

 response for the Israeli breakwaters was observed to reach a mature age about 

 5 years after construction was completed; adjacent beaches suffered severe 

 erosion during the first 3 to 4 years (or longer) after construction. 

 Gourlay (1981) 



16. Gourlay (1981) presents similar relationships based on physical 

 model and field observations. Based on the laboratory studies of Sauvage de 

 St. Mark and Vincent (1955), Adachi, Sawaragi, and Ogo (1959), and Shinohara 

 and Tsubaki (1967), Gourlay reaches the following conclusions for laboratory 

 response to detached breakwaters: 



a. Tombolos can form only if the structure is located in the surf zone. 



b. Noninterfering diffraction patterns, resulting in two independent 

 current systems (and possibly double tombolo formation) , exist for 

 the following structure -distance ratio: 



10 



