80 HAUPT — METHODS OF IMPROVING OCEAN BARS. [May 3, 



nishes no illustration of a deep pocket at both ends of a contracted 

 pass, whether natural or artificial. High tide jetties, unfortunately, 

 greatly obstruct the ingress of the tides and hence reduce the vol- 

 ume available for ebb scour, and it was to meet this condition that 

 the reaction breakwater was, in part, designed with such marked 

 results. 



The former method proposed for overcoming this objection was, 

 as the author states, to increase the width between the jetties on 

 the bar and to build them only to near low-water mark, but, as he 

 adds, the scouring effect has not produced depths great enough for 

 navigation — although "dredged channels can be maintained at 

 comparatively moderate cost," as at Charleston, which is cited as 

 " a good example." 



Here, again, it would seem that the reference is unfortunate, in- 

 asmuch as the Government dredge was unable to maintain the chan- 

 nel on the ranges, and a new and more powerful machine is build- 

 ing, while the bar has reformed three-quarters of a mile beyond the 

 jetties, and the outer twenty-six-foot contour is 1.5 miles to sea- 

 ward of them. The jetties were reported completed several years 

 since, at a cost of about $4,000,000, but they have failed to hold the 

 bar, which has eluded them and gone to sea, where dredging is 

 now required in open water. The author recognizes this feature 

 in his report, wherein he says : 



" The Charleston jetties have been left low near the shore for the 

 double purpose of economy in construction and to freely admit the 

 flood tide to avoid reduction in the tidal prism. It is not unrea- 

 sonable to believe that the quantity of dredging necessary and the 

 quantity of sand that have been scoured seaward has been mate- 

 rially increased by sands driven over the low portion of the north 

 jetty by the northeast storms. Such sand may be expected to be 

 driven into the channel, usually over both jetties, if they are left 

 low, even though the predominance of -sand movement is in one 

 direction." 



This statement is undoubtedly correct and clearly recognizes one 

 of the defects of twin jetties, submerged at their shore ends, and 

 yet one of the officers recently in charge of that work stated 

 officially : 



"I have been out on that bar for thirteen years, day in and day 



out I know that on top of those rocks there never was sandf 



.... I have never found it there." His contention being that it 

 did not travel over the submerged ends of the jetties. 



