material is used to maintain the spit, with the remainder being bypassed to 

 the downdrift beaches. 



f. Hillsboro Inlet, Flori da (Hodges, 1955; Jones and Mehta, 1977). 

 Hillsboro Inlet is a natural inlet in Broward County, Florida, about 58 

 kilometers (36 miles) north of Miami. A unique aspect of the inlet is a 

 natural rock reef that stabilizes the updrift (north) side of the channel (see 

 Fig. 6-49). The rock reef and jetties form what is called a sand spillway. 

 Southward-moving littoral sand is washed across the reef and settles in the 

 sheltered impoundment area where it is dredged and bypassed to the south 

 beaches. A 20-centimeter hydraulic dredge, purchased by the Inlet District in 

 1959, operates primarily in the impoundment basin, but also maintains the 

 navigation channel. The total quantity of sand bypassed between 1952 and 1965 

 was 589,570 cubic meters (771,130 cubic yards), averaging 45,350 cubic meters 

 (59,300 cubic yards) per year. 



The north and south jetties were rebuilt and extended during 1964-65, and 

 the navigation channel was excavated to -3 meters MSL. Between 1965 and 1977 

 the dredge bypassed 626,000 cubic meters (819,000 cubic yards) of sand for an 

 annual average of 52,170 cubic meters (68,250 cubic yards) per year. 



This sand-bypassing operation is the origianl weir jetty, and it forms 

 the basis for the type V bypassing concept. 



g. Masonboro Inlet, North Carolina (Magnuson, 1966; Rayner and Magnuson, 

 1966; U.S. Army Engineer District, Wilmington, 1970.) This inlet is the 

 southern limit of Wrightsville Beach, North Carolina. An improvement to 

 stabilize the inlet and navigation channel and to bypass nearly all the 

 littoral drift was constructed in 1966. This phase of the project included 

 the north jetty and deposition basin. The jetty consisted of an inner section 

 of concrete sheet piles 520 meters (1,700 feet) long, of which 300 meters is 

 the weir section, and a rubble-mound outer section 580 meters (1,900 feet) 

 long. The elevation of the weir section (about midtide level) was established 

 low enough to pass the littoral drift, but high enough to protect the dredging 

 operations in the deposition basin and to control tidal currents in and out of 

 the inlet. The midtide elevation of the weir crest appears to be suitable for 

 this location where the mean tidal range is about 1.2 meters. The basin was 

 dredged to a depth of 4.9 meters (16 feet) MLW, removing 280,600 cubic meters 

 (367,000 cubic yards) of sand. A south jetty, intended to prevent material 

 from entering the channel during periods of longshore transport reversal, was 

 not initially constructed. Without the south jetty, sand that entered the 

 inlet from the south caused a northward migration of the channel into the 

 deposition basin and against the north jetty. Between 1967 and 1979 all 

 dredging operations were involved in channel maintenance. 



In 1980 the south jetty (see Fig. 6-50) was completed, and 957,000 cubic 

 meters (1,250,000 cubic yards) of material was dredged from the navigation 

 channel and from shoals within the inlet. This material was placed on the 

 beach. It is expected that the south jetty will prevent the navigation chan- 

 nel from migrating into the deposition basin, and that the weir- jetty system 

 will function as originally designed. It is projected that 230,000 cubic 

 meters (300,000 cubic yards) of material will be impounded in the basin each 

 year and hydraulic bypassing will alternate each year between Wrightsville 

 Beach to the north and Masonboro Beach to the south. 



6-74 



