unique. Ultimately, the dredge operated in seas up to 1.5 meters; when the 

 seas exceeded 2 meters (6 feet), it proceeded to Redondo Harbor for shelter. 

 Of particular interest in this project is the use of a pipeline dredge in a 

 high wave energy coastal area. This area is subject to high-energy waves with 

 little advance warning. These waves can quickly exceed the operating 

 conditions of the dredge. 



The dredge was held in position with its beam to the sea by an arrange- 

 ment of the stern and bowlines. On the end of the dredge ladder was a 

 combination head that provided both cutting and suction action. The force to 

 lift the suspended material was provided by a suction pump in the dredge well, 

 assisted by water jets powered by a separate 185-k.ilowatt (250-horsepower) 

 pump. Sand was removed by working the head down to the bottom of the cut and 

 keeping it in that position until the sandy material stopped running to the 

 head. The head was then raised, and the dredge would pivot about 12 meters 

 (40 feet) to the next position in the cutting row, where the process would be 

 repeated. The dredge could cut a row 76 meters (250 feet) wide. At the 

 completion of a row, the dredge was moved ahead on its lines about 12 meters 

 for the next row cut. For most of the Redondo Beach project it was possible 

 to excavate to -17 to -20 meters (-55 to -65 feet) with a cutback of 6 to 9 

 meters (20 to 30 feet). This is desirable for high production because it 

 minimizes moving and swinging of the dredge. 



The sand slurry was transported ashore through a combination pontoon and 

 submerged line. The pontoon line was a 40-centimeter-diameter pipe supported 

 in 18-meter lengths by steel pontoons. The submerged steel pipeline was 

 joined to the floating line by a flexible rubber hose. As the beach fill 

 progressed, the submerged line was moved by capping the shore end of the 

 discharge and then pumping water out of the line. This created a floating 

 pipeline that was towed to the next discharge position. As pumping resumed, 

 the pipeline filled and sank to the bottom. 



The fill was accomplished by a double-pipe system. The system consisted 

 of a yoke attached to the discharge line and, by use of a double-valve 

 arrangement, the discharge slurry was selectively distributed to either one 

 pipe or the other, or to both pipes simultaneously. The beach was built by 

 placing the first discharge pipe at the desired final fill elevation, in this 

 case at +3.7 meters MLLW, and pumping until the desired elevation was 

 reached. By alternating between the two discharge lines, the beach width of 

 60 meters (200 feet) was built to the full cross section as they advanced. 

 The final placement (see Fig. 6-21) totaled 1.1 million cubic meters (1.4 

 million cubic yards) at a cost of $1.5 million. Between 3000 and 11,500 

 cubic meters (4,000 and 15,000 cubic yards) per day were placed on the beach, 

 averaging 6,000 cubic meters (8,000 cubic yards) per day. The work was 

 completed in October 1968. 



A substantial reduction in beach width occurred during the first year. 

 Some of the fill material was transported onto the backshore above the +3.7- 

 meter MLLW contour. More material was transported offshore. While these 

 initial changes did reduce the beach width, they also increased beach stabil- 

 ity, and the rate of retreat dropped significantly in subsequent years. A 

 recent study (Hands, in preparation, 1985) documents the long-term stability 

 of the fill material at Redondo Beach. No additional maintenance material 

 has been placed on the beach to date (1981), and after 12 years much of the 



6-31 



