dredge requires disposal areas with enough depth to allow dumping. The 

 hopper dredge is not suitable for bypassing operations unless it dis- 

 charges in an area where the material may be rehandled by another type 

 of dredge or is equipped to pump the material ashore. Since about 1960, 

 a number of hopper dredges have been equipped to pump the material from 

 their bins; thus the hopper dredge has greatly increased in importance 

 in bypassing operations. 



Mechanical dredges require auxiliary equipment (such as dump scows, 

 conveyors and eductors) to transport material to the point of placement. 

 Equipment and techniques are continually being improved in the transpor- 

 tation of sand; therefore, incoiporating a mechanical-type dredge to by- 

 pass material may be most favorable in some cases. In considering a 

 floating dredge for a bypassing operation, each type of dredge plant must 

 be evaluatedo This evaluation should include: first, the feasibility of 

 using various types of floating dredges; second, the operational details; 

 and finally, the economics to determine which floating plant will transfer 

 the material at the least unit cost. Local site conditions will vary, and 

 factors to be considered for each type of floating plant cannot be stand- 

 ardized. Some of the more important factors to evaluate follow: 



a„ Exposure of Plant to Wave Action . Wave action limits the effec- 

 tive operation of a floating dredge; the exact limitation depends on plant 

 type and size, and intensity of wave action. This factor is particularly 

 critical if the dredge will be exposed to open waters where high waves may 

 be expected. No standard criteria are available for the maximum permissi- 

 ble wave action for operation of various types of dredges. Such data must 

 be obtained from dredge operators who are familiar with the dredge plant 

 and the area in question. However, as mentioned in Section 6.3 PROTECTIVE 

 BEACHES, a specially designed pipeline dredge has been used successfully 

 at Malaga Cove (Redondo Beach), California, for pumping sand to the beach 

 from offshore in an exposed location. Hopper dredges may be operated in 

 higher waves than the other types of floating dredge plants. Pipeline 

 dredges exposed to hazardous wave action are subject to damage of the 

 ladder carrying the suction line, breakage of spuds, and damage of the 

 pontoon-supported discharge pipe. Thus, estimates must be made of the 

 probable operational time with and without manmade structures or natural 

 ground features to protect the dredge and auxiliary equipment. Determi- 

 nation of the time of year when least wave action will prevail will allow 

 estimates to be made for plant operation under the most favorable conditions. 

 Also, protection of the plant during severe storms in the area of the pro- 

 ject must be considered. 



b. Plant Capacity . Use of a floating dredge of a specific capac- 

 ity is generally controlled by economic consideration. If the impounding 

 zone of a littoral barrier is large, a periodic bypassing operation may 

 be considered in which a large plant is scheduled and utilized for short 

 periods of time. An alternative would be the use of a small-capacity 

 plant for longer periods of time. If long pumping distances to the dis- 

 charge point necessitate too many booster pumps, a larger plant may pro- 

 vide most economical operation. The choice sometimes depends on avail- 

 ability of plant equipment. 



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