pile bulkhead Tri.ll be built from C to D to protect the beach and dredge 

 from ocean vraves. The drag-line has been in operation for about six 

 months. The operators believe that one -fourth of the sand scheduled 

 for removal has been taken out. 



It is too early to predict the general effectiveness of this 

 fixed dredge installation. The beach most certainly was receding as 

 of November 1, 1951. As-showi on Figure 2, the shore line has gone 

 back 30 or 4.0 feet from the position as shown on the design drawings. 

 The posit ion of the shore line as shown in a photograph in the Beach 

 Erosion Ifeport (Bulletin, 1 July 1951) taken a short time prior to 

 November 1950 is essentially the same as the position in November 1951. 

 If the position in November 1951 is the same as that of 12 months or 

 more earlier and if the beach is now receding, it would seem as if the 

 beach had advanced and then retreated during the year. The question 

 then arises as to xvhether the beach is now receding mainly as a result 

 of the dredgir^ action of the drag-line operations or is receding 

 seasonally because of higher waves or higher tides, as is the •'custom 

 of many beaches. Theoretically it would seem as if the drag line 

 operations were removing sand from the beach, thus facilitating the 

 recession of the shore line. If so, then in time the beach should 

 attain some position vriiereby sand could progress directly into the 

 dredging pit and be removed. It would be desirable to re-examine the 

 beach in 6 months or a year to determine the rate of recession. 



As shorm in Figure 2, a permanent pile bulkhead is ultimately 

 planned along line CD to protect the beach and dredge from the waves # 

 This bulkhead is convex seaward, v/hereas most stable beaches between 

 points of obstruction are concave seaward. It will be interesting 

 to see if the beach does attain a stable convex shape, while at the 

 same time supplying the dredging pit with sand. An alternative that 

 might be considered is to allow or cause the beach to achieve a concave 

 profile extending from the granite porphyry rock to the dredge (Figure 

 2). Hovraver the radius of curvature of such a beach that would be 

 necessary to cause effective natural transmission of sand to the 

 dredging pit might be too short for the beach to remain in equilibrium 

 with the result that the beach would build seaward to an extent that 

 sand could not enter the dredging pit. In such an event the rocky 

 mass of porphyry 1/4. mile west of the dredge, might be removed in order 

 to provide a greater recession of the shore line and a longer and 

 perhaps more stable radius of curvature of the beach. One compilation 

 of such a configuration of shore line would be direct approach of waves 

 to the fixed dredge, which in time of storm might cause serious pro- 

 blems . 



Even though a fixed dredge, such as the one at Salina Cruz should 

 prove to be an effective means of combating surplus sand in harbors, 

 the comparative cost of operation and amortization relative to the 

 cost of periodic removal of sand from the harbor by floating dredge 

 is also a factor to be considered. It would seem as if a satisfactory 

 dredge could never trap all the sand that moves along the beach and in 



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