1955.) At Durban, the plant bypassed about 200,000 cubic yards of sand 

 per year from 1950 to 1954; afterward the amount decreased. The plant 

 was removed in 1959 when not enough littoral drift reached it. No appar- 

 ent reduction in maintenance dredging of the harbor entrance channel took 

 place during the 9 years of bypassing operations. Starting in 1960, the 

 material dredged from the channel was pumped to the beach to the north by 

 a pump-out arrangement from the dredge and booster pumps along the beach. 



6.511 South Lake Worth Inlet, Florida . (Watts, 1953). South Lake Worth 

 Inlet, about 15 miles south of Lake Worth Inlet and about 10 miles south 

 of Palm Beach, was dredged, and two entrance jetties were constructed in 

 1927. The primary purpose of this inlet was to create a circulation of 

 water in the south end of Lake Worth, to lessen a stagnant water condi- 

 tion. The inlet channel also permits passage of craft drawing up to 6 or 

 8 feet. It is 125 feet wide and 600 feet long. The entrance jetties are 

 250 feet long. Their top elevation is 12 feet above mean low water. 

 After jetties were built, the downdrift beach south of the inlet eroded. 

 Construction of a seawall and groin field failed to stabilize the shore- 

 line. A fixed sand bypassing plant began operation in 1937. (See Figure 

 6-43.) The initial plant was designed to bypass enough sand over 2 years 

 to fill the groins and protect the seawall. Design capacity did not in- 

 clude consideration of total longshore transport. The plant consisted of 

 an 8-inch suction line, a 6-inch centrifugal pump driven by a 65-horsepower 

 diesel engine, and about 1,200 feet of 6-inch discharge line that crossed 

 the inlet on a highway bridge. The outfall was located on the beach south 

 of the south jetty. 



The plant, with a capacity of about 55 cubic yards of sand per hour, 

 pumped an average of 48,000 cubic yards of sand a year for 4 years. The 

 net north-to-south longshore transport rate was estimated to be about 

 225,000 cubic yards a year. After 5 years (1937-1941), the beach was 

 partially restored for more than a mile downcoast. During the next 3 

 years (1942-1945), pumping was discontinued, and the beach south of the 

 inlet severely eroded. In 1945, the plant resumed operation, and the 

 shore immediately south of the inlet was stabilized. To reduce shoaling 

 in the inlet channel, the size of the bypassing plant was increased to 

 an 8-inch pump with a 27-horsepower diesel engine with a capacity of 

 about 80 cubic yards of sand per hour. This plant bypassed about one- 

 third of the available littoral drift. The remainder, about 150,000 

 cubic yards, was transported by waves and currents to the offshore zone, 

 the middleground shoal, and the downdrift shore. 



6.512 Lake Worth Inlet, Florida . (Zermuhlen, 1958, and Middleton, 1959). 

 Lake Worth Inlet is at the north limit of Palm Beach, Florida. The fixed 

 bypassing plant is a two- level, reinforced concrete structure near the 

 end of the north jetty. (See Figure 6-44.) On the lower level (1 foot 

 below MLW) are a centrifugal dredge pump, a 400-horsepower electric motor, 

 and a power transformer. The upper level houses controls and ventilating 

 equipment. The pump has a 12-inch suction and 10-inch discharge, and is 

 designed to handle 15 percent solids at more than 60 percent efficiency. 

 Design capacity was about 170 cubic yards per hour. The suction line is 



6-56 



