1S69.] ^"* [Haupt. 



During the work of construction some of the cribs near the shore were 

 broken up and washed away. 



"When the work was suspended it is said there was a twelve foot chan- 

 nel across the bar, which was maintained for several months, possibly 

 until the teredo and the waves had destroyed a considerable part of the 

 frail cribwork. 



"In 1871, when the late Lieut. E. A. Woodruff made a reconnoissance 

 of the pass, he was unable to find any trace of the work. It is said that 

 as the work gradually disappeared the channel across the bar gradually 

 returned to its normal depth. I consider my information reliable as to 

 the above described work and its effects." 



These extracts show very conclusively that, so far as this frail structure 

 went, it was in the proper place, and did effective work in improving the 

 channel by keeping out the sand and preventing the dispersion of the ebb. 

 Its form and materials might have been improved to great advantage. 



The Government failed to profit by this precedent, however, for in 

 August, 1887, the engineer officer in charge of this pass, reported that : 



"The work designed to deepen the channel over the bar, consisting of 

 a single jetty, constructed upon the south side of the entrance, has had no 

 important effect upon the bar, and is in a dilapidated condition. The 

 channel depth, over the bar, is now eight and one half feet, and the 

 channel crosses the jetty." 



Thus it appears that this jetty was attempted on the wrong side (the 

 south) of the channel, and that the ebb discharge in seeking the line of 

 least resistance was forced over the crest of the submerged work by the 

 bar of sand rolled up by the flood component. 



JETTIES IN PAIRS. 



This paper would be incomplete without the evidence collected by ex- 

 perienced maritime engineers of other countries, as to the results of similar 

 works elsewhere. 



In his digest of jettied entrances, Sir Vernon Harcourt says in general 

 of the jetty system : 



"The jetties also, in most cases, were extended in the hope of reaching 

 deep water, which proved fruitless, owing to the progression of the fore- 

 shore with each extension of the jetties. Next artificial sluicing basins 

 were formed, to provide a larger mass of water for sluicing, with the ad- 

 ditional advantage that the issuing current was nearer and better directed 

 for scouring the entrance. Lastly, dredging with sand-pumps is being 

 largely employed for deepening the channel beyond the jetties. The 

 parallel system has not proved successful in providing a deep entrance 

 without constant works. * * * Experience has shown how jealously 

 encroachments on the tide-covered lands should be prevented, and the 

 uselessness of prolongations of the jetties. * * * Parallel jetty harbors 

 are one of the most difficult class of harbors to design and maintain suc- 

 cessfully." 



