Indian River 



A ) ^r Permeable Jetty 



Deposition Area 



ATLANTIC 

 OCEAN 



\s tr 



Figure 9. Deposition area in a spit at St. Lucie Inlet, Florida. 



4. Deposition Basin. 



Characteristics that must be determined in a design of the deposition area 

 are basin location, shape, and capacity. 



Basin location and shape are dictated mostly by existing inlet geometry 

 and the desired location of the navigation channel. The deposition area is 

 usually adjacent to or behind the weir section as in the case of a shore- 

 parallel weir (e.g., at Hillsboro Inlet). The basin should be positioned far 

 enough from the base of the weir and jetty to preclude the jetty from sliding 

 into the basin as a result of slope failure. In some cases, the deposition 

 area may be located a distance from the weir in the form of a sandspit that 

 may develop in the bay behind the inlet throat, e.g., St. Lucie Inlet. The 

 expected response of the navigation channel to jetty construction must be 

 considered in selecting the location of the deposition basin. Sheltering of 

 the navigation channel by the jetties and thus excluding the normal sand 

 transport into the channel usually results in channel reorientation shortly 

 after construction. Removal of some factors that hold the unimproved inlet in 

 a state of equilibrium may lead to channel migration into the proposed deposi- 

 tion area. Providing room for a deposition basin between two jetties usually 

 requires an "arrowhead" jetty layout or a modification thereof. If there is a 

 tendency for the navigation channel to meander, its movement into the deposi- 

 tion basin is possible. In this case, a training dike may be required to fix 

 the channel location between the jetties in the reach from the inlet entrance 

 at the seaward end of the jetties, past the deposition basin and into the 

 inlet throat (Fig. 10). Construction of such a dike, if needed, will con- 

 tribute to the cost of a weir-jetty bypassing system even though its crest 

 elevation need not be high. 



23 



