33. Well-developed tombolos were observed to form when 



X 



^ 0.56 (35) 



and a bimodal tombolo developed for 



X 



y 0-39 (36) 



The total amount of sand deposition per unit width of gap was observed to be 

 about three times the quantity of material transported shoreward through a 

 permeable breakwater, when dimensions of the structures are "chosen appro- 

 priately." When structures were placed seaward of the breaker line, no sand 

 was observed to move seaward through the structures; when structures were 

 placed near the shoreline, Noda observed that sand may move offshore. 

 Hallermeier (1983) 



34. In a review of field and laboratory sediment depositional patterns 

 in the vicinity of coastal structures, Hallermeier (1983) developed a rela- 

 tionship for the depth limit of sediment transport. Hallermeier recommends 

 the following depth as a guide when positioning detached breakwaters when 

 tombolo formation is deemed undesirable: 



110 Hi 



V(5 - 1) (5 - 1) gr Ti 



depth for salient formation (37) 



where 



dga = annual seaward limit of the littoral zone 



//g = deepwater wave height exceeded 12 hr per year 



S = ratio of sediment to fluid density 



g = acceleration of gravity 



Tq = wave period corresponding to H^ 



35. For headland structures (tombolo development), structures should be 



sited near 



d = -^ headland structures (38) 



22 



