and which became available after Model B was run, seem to indicate erosion 

 rates of the order of 0.8 ft/year or less between sta 325+57 and sta 361+74 

 and deposition rates of the order of 1.4 ft/year or less between sta 361+74 

 and sta 399+74. In view of the uncertainty on sedimentation rates in the 

 length of channel between sta 325+00 and sta 399+74, and because the existing 

 depths in this reach are generally higher than 49 ft mlw, an advance mainte- 

 nance depth of 3 ft is recommended in this reach. 



132. For convenience in dredging, the channel was divided into reaches 

 of at least 2,000-ft lengths at the suggestion of CESAJ. Table 5 lists the 

 various reaches of Plan 1 entrance and offshore channels where shoaling is 

 expected, estimates of deposition rates (rounded to 0.1 ft/year), and recommen- 

 dations for advance maintenance depths (rounded generally to whole feet) . If 

 the length of channel between sta -97+76 and sta 325+00 is considered and only 

 the rectangular portion of the planned channel cross section is taken, the 

 total dredging volume for advance maintenance in accordance with the recommen- 

 dations shown in Table 5 represents a savings of approximately 630,000 cu yd, 

 or nearly 27 percent, compared to the dredging volume for a channel with 3-ft 

 advance maintenance throughout this reach. 



133. The recommendations given in Table 5 do not take into account the 

 long-term economic advantages of providing greater advance maintenance depths 

 and dredging less frequently than once a year, especially in the offshore 

 areas, in view of the high cost of mobilization of dredging plant. This issue 

 should be explored before a final decision is made on advance maintenance 

 depths. 



134. From the geologic sections provided by CESAJ, rock seems to be 

 present at depths of 40 to 54 ft mlw between sta 234+00 and 260+00. Two of 

 the reaches where large advance maintenance depths of the order of 7 to 9 ft 

 have been recommended are in this general area. This is the area just outside 

 of the jetty tips and just interior to the jetties. Severe deposition prob- 

 lems have been experienced in this general area at present because of material 

 moving from the shoals on either side of the channel into the channel. Gener- 

 ally, the highest deposition rates have been observed in the northernmost 

 quadrant of the channel. In view of the difficulty and expense of dredging in 

 rock and problems that may be experienced with large overdepth dredging, it is 

 suggested that overwidth dredging be explored as an alternative to overdepth 

 dredging in this area. For instance, in addition to providing a reasonable 



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