area is protected from waves by the weir and jetty. Sand is pumped from the 

 deposition basin to nourish the downdrift beach. The jetties fix the location 

 of the navigation channel; the updrift jetty controls the transport of sand 

 into the deposition basin, controls alinement of the updrift beach, and pro- 

 vides protection to a dredge operating in the deposition basin. 



II. WEIR- JETTY SYSTEM 



The key elements of a weir-jetty system (Fig. 5) are: (a) An updrift 

 jetty comprised of a sandtight landward section, a weir section with an 

 elevation near mean sea level (MSL) , and a seaward section with a typical 

 jetty cross section; (b) a downdrift jetty which normally has a typical jetty 

 cross section without a weir; (c) a deposition basin; (d) a navigation chan- 

 nel; (e) an updrift beach; and (f) a downdrift beach which normally also 

 serves as the disposal area for sand removed from the deposition basin. The 

 design objectives of each element are discussed below and, in more detail, in 

 Section III. 



Updrift Beach 



OCEAN 



BAY 



— -t"^~^; 



Jetty 



Figure 5. Key elements of a typical weir-jetty system. 



A weir-jetty system is a multiple-purpose coastal structure system that 

 serves what at times may be conflicting uses. It primarily serves navigation 

 by keeping the location of the channel through a tidal inlet relatively fixed 

 with adequate water depths to provide safe passage for vessels. The remaining 

 functions arise because of a need to bypass sand to downdrift beaches and to 

 improve flushing of the navigation channel. 



13 



