SUB-STATION 



The sub-station (booster pumping plant) was built to aid the 

 dredge pumps in moving the dredge material . At the sub-station there 

 are two pumps each run by a 450 hup. electric motor similar to those 

 on the dredge. Also at the sub-station there are duplicate pumps 

 for refrigeration, fuel, etc. The motors which operate this auxiliary- 

 equipment are run by electricity supplied at the rate of 40 h.p. at 

 4.00 volts through a transmission line from the dredge. Three #00 

 copper wires are used for the transmission line. 



All of the pipe is 18 inch diameter steel and is run exposed so 

 that it may be inspected at any time . In the beginning the practica- 

 bility of laying the pipe along the bay and crossing the repair 

 basin entrance by means of a siphon was considered. This however was 

 discarded in favor of the present method due to the possibility of 

 deteriation of the submerged pipe. 



At the foot of the lighthouse bluff, west of the fixed dredge, 

 a jetty is being constructed at the least possible cost. With it, 

 it is hoped to impound the littoral drift from the west, forming 

 a bank of sand that will not have to be dredged, thus prolonging 

 the useful life of the Draga Fija. 



Eventually the sand that collects at the end of the jetty will 

 be in a depth less than five or six meters. When this occurs, 

 the action of the surf will be capable of lifting the sand and 

 starting it on its eastward journeyo This is the only sand that 

 the fixed dredge will have to pump. 



It has been calculated that a jetty five or six hundred meters 

 long will impound sand for two hundred years. However, when a beach 

 is formed near the end of the jetty surf action will cause the sand 

 to be transported to the east. This is the limiting point of the 

 jetty's effectiveness. 



As yet it is not known whether or not it would be more economical 

 to construct such a jetty or to pump sand that would be trapped by 

 it, nor is it known which method would be the more effective . The 

 answer to these questions can be resolved only through experience. 

 For the present the littoral drift will be allowed to go directly 

 to the dredge. 



However, it would be well to consider the construction of this 

 jetty for though it might cost a little more to retain the sand 

 than to pump it, the jetty would prolong the life of the dredgp. 

 In either case, whether by the joint function of the jetty and the 

 dredge or by the operation of the dredge alone, sand will be pre- 

 vented from entering the Bay of Salina Cruz . 



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