a 20-centimeter discharge line. This plant yielded an average discharge of 75 

 cubic meters (100 cubic yards) per hour. The remainder of the littoral drift 

 was transported by waves and currents to the offshore zone, the middle ground 

 shoal, and the downdrift shore. 



In 1967 the north jetty was extended and the bypassing plant was moved 

 seaward (see Fig. 6-40). The current plant consists of a pump, a 300-k.ilowatt 

 (400-horsepower) diesel engine, and a 30-centimeter-diameter suction line. 

 The estimated discharge is 150 cubic meters (200 cubic yards) of sand per 

 hour. During the period 1968 to 1976, the plant averaged 53,800 cubic meters 

 (70,300 cubic yards) of bypassed material per year. 



In addition to the fixed plant, a hydraulic pipeline dredge has also been 

 used to bypass sand from the middle-ground shoals. Between 1960 and 1976, the 

 average annual volume of bypassed dredge material was 20,000 cubic meters 

 (26,000 cubic yards). 



b. Lake Worth Inlet, Florida (Zermuhlen, 1958; Middleton, 1959; Jones 

 and Mehta, 1977). Lake Worth Inlet, located at the northern limit of Palm 

 Beach, was cut in 1918 and stabilized with bulkheads and jetties between 1918 

 and 1925. The fixed sand-bypassing plant began operation in 1958. The plant 

 (see Fig. 6-41) consists of a 300-kilowatt (400-horsepower) electric motor and 

 pump combination, a 30-centimeter suction line, and twin 25-centimeter 

 discharge lines (added in 1967) which traverse the inlet on the channel 

 bottom. A 240-meter section of the submerged discharge line can be removed 

 during maintenance dredging of the navigation channel. The system was 

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

 Design capacity was about 130 cubic meters (170 cubic yards) per hour. The 

 plant can dredge within a 12-meter sector adjacent to the north side of the 

 plant to a depth of -3.7 meters MLW. A complex emergency flushing system, 

 which was never used, was removed in 1971 because of high maintenance costs. 



The average annual amount of bypassed material between 1958 and 1966 was 

 57,700 cubic meters (75,500 cubic yards) per year. In 1969 the groin to the 

 north of the plant was removed. The original intent of the groin was to pre- 

 vent the plant from bypassing too much material, which might cause the updrift 

 beaches to recede. However, the effect of the groin was to impede the move- 

 ment of sand toward the pumping area. After removal of the groin, the average 

 annual amount of bypassed material increased to about 99,000 cubic meters 

 (130,000 cubic yards) per year during the period from 1969 to 1976. This 

 estimate, based on an average discharge rate of 150 cubic meters per hour, 

 represents about 60 percent of the estimated annual littoral drift. 



In addition to the fixed bypassing plant, material dredged during channel 

 maintenance has been placed south of the inlet. In the 3-year period from 

 1970 to 1973, a total of 227,000 cubic meters (297,000 cubic yards) was 

 bypassed by hydraulic dredge. 



c. Rudee Inlet, Virginia Beach, Virginia (Richardson, 1977). Rudee 

 Inlet, immediately south and updrift of Virginia Beach, was essentially 

 nonnavigable until 1952 when two short jetties were built and a channel was 

 dredged. The channel immediately began to shoal with littoral material, and 

 erosion occurred on the downdrift beaches. A fixed bypassing plant with 

 a small capacity was installed in 1955 with little effect, and a floating 



6-56 



