6.524 Hillsboro Iiilet, Florida . (Hodges, 1955). This inlet is about 36 

 miles north of Miami Beach. Sand bypassing operations have been by a 

 pipeline dredge. (See Figure 6-48.) This method is well suited for this 

 location, because the littoral material moving to the south is impounded 

 in an area sheltered by a rock reef and rubble-mound jetty. The rock 

 reef and jetty form what has been termed a sand spillway . Dredging the 

 sand behind the spillway and depositing it on the downdrift beach has 

 helped keep the inlet open and has provided nourishment to the downdrift 

 beach. Experience has indicated that about 75,000 cubic yards of sand 

 should be bypassed each year. This plan is the original weir jetty , and 

 forms the basis for the Type IV design concept. 



6.525 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 of the littoral drift has been partly constructed. 

 The part completed in 1966, comprised the north jetty and deposition 

 basin. (See Figure 6-49.) The jetty consists of an inner section 

 1,700 feet long of concrete sheet piles, of which 1,000 feet is the 

 weir or spillway section, and a rubble-mound outer section 1,900 feet 

 long. The elevation of the weir section (about half-tide level) was 

 established low enough to pass the littoral drift, but high enough to 

 protect a dredge in the deposition basin, and to control tidal currents 

 in and out of the inlet. The elevation appears to be suitable for this 

 location where the mean tidal range is about 4 feet. The basin was 

 dredged to a depth of 16 feet, mean low water, and 367,000 cubic yards 

 of sand were removed. It was planned to redredge the basin at 2-year 

 intervals, and deposit the material to nourish and stabilize downdrift 

 shores. A south jetty, intended to prevent material from entering the 

 channel during periods of longshore transport reversal, has not been 

 built. Without the south jetty, sand that enters the inlet from the 

 south has caused a northward migration of the channel into the deposi- 

 tion basin and against the north jetty. Because migration of the 

 channel has caused navigation problems, model studies are presently 



in progress to establish the final design of the inlet including the 

 alignment and dimensions of the south jetty. 



6.526 Perdido Pass, Alabama . This weir-jetty project was completed in 

 1969. (See Figure 6-50.) Since the direction of longshore transport 

 is westward, the east jetty included a weir section 1,000 feet long at 

 an elevation 1/2 foot above mean low water. The diurnal tidal range is 

 about 1.2 feet. A deposition basin was dredged between the weir adja- 

 cent to the 12- foot-deep channel. Scour along the basin side of the 

 concrete sheet pile weir was remedied by placing a rock toe on the weir. 

 Nearly all the littoral drift crosses the weir. The deposition basin 

 filled so rapidly that the fill encroached on the channel. Redredging 

 of the basin was necessary in 1971. 



6.527 Other Floating Plant Projects . Other sand bypassing projects using 

 floating dredges are at the following locations: 



6-65 



