The alinement of the weir section, with respect to the updrift beach, is 

 usually dictated by inlet geometry and the presence of shoals that can form a 

 satisfactory foundation for the structure. Construction over existing shoals 

 will lower costs by minimizing the amount of materials needed and by alining 

 the structure to achieve the shortest possible jetty length. The effect on 

 sediment transport characteristics of weir-section alinement, with respect to 

 the shoreline, does not appear to be significant. Existing weir jetties have 

 weir alinements ranging from shore-parallel weirs to weirs that are perpen- 

 dicular to the updrift shoreline (see Table 1). The weir at Hillsboro Inlet, 

 Florida, which served as the prototype for the weir-jetty concept, is nearly 

 parallel with the updrift shoreline; the weir section in the north jetty 

 at Masonboro Inlet, North Carolina, is nearly perpendicular to nearby 

 Wrightsville Beach. The weir sections at both Murrells and Little River 

 Inlets, South Carolina, are alined at an angle of approximately 45° with the 

 updrift beach. Although this range of angles is relatively large, the sedi- 

 ment transport conditions at any of the existing weirs do not appear to be 

 impaired. Shore-parallel weirs are preferable since the possibility of sand 

 being transported past the sandtight seaward end of the jetty is smaller. 

 Thus, it is more likely that all of the sand transported to the weir will be 

 carried over it into the deposition basin with less sand eventually entering 

 the navigation channel. 



The size and location of the deposition basin influence the weir alinement 

 which must provide adequate area for locating a basin within the inlet. The 

 basin must also be positioned to trap the sand transported over the weir; 

 ideally, it should be placed to afford maximum protection for a dredge oper- 

 ating in the basin. These factors vary from site to site and depend on pre- 

 vailing inlet geometry. 



A critical jetty design factor is to establish the location of the land- 

 ward end of the weir section. The jetty section connecting the weir with the 

 shoreline should be sandtight to hold the updrift beach in a dynamically 

 stable planform. The length of the sandtight shore section is determined from 

 the desired updrift beach configuration. If the sandtight section is too 

 short, the erosion which occurs during reversals may endanger a significant 

 area updrift of the inlet; if too long, a large volume of sand accumulates in 

 the updrift beach. Ideally, the amount of sand stored in the updrift fillet 

 should be the amount needed to nourish updrift beaches when the longshore sand 

 transport is in the updrift direction. 



Weir sections in earlier projects (Perdido Pass, Alabama; East Pass, 

 Florida; and Masonboro Inlet) are of sheet-pile construction; recent projects 

 (Murrells and Little River Inlets) have been designed with rubble-mound weirs. 

 Sheet-pile weir sections were constructed because of their relatively low 

 initial cost when compared to rubble construction; however, smooth-faced 

 sheet-pile weirs have been found to reflect waves and cause confused wave 

 conditions in their vicinity. The effect of these confused wave conditions on 

 sediment transport across the weir is unknown; however, they are considered 

 detrimental. Currents along the weir are also more likely to occur if sheet- 

 pile construction is used. These currents may result in a decrease in trans- 

 port over the weir and an increase in transport along the weir, with the sand 

 eventually entering the navigation channel. Present practice is to construct 

 the weir section of rubble with one or more rows of quarrystone with their 

 crests at the desired weir elevation to minimize the confused wave conditions 



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