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



other cases. This single jetty is, however, but the incompleted part 

 of a twin jetty project and hence was not designed to operate as a single 

 reaction jetty at all. The total appropriations were $888,750, 

 while the estimated amount to complete the twin jetties to secure 

 twenty feet is $1,791,412.20; total, $2,680,162.20. The bar is 

 moving seaward at a more rapid rate than ever, and is now about 

 1800 feet beyond the jetty. Its average rate is 200 feet per annum. 



The question may well be asked, Why build this second jetty, at 

 so great cost, if the depths are already over twenty feet, and if 

 dredging is so much cheaper? The map however shows why, since 

 a sand spit extends from the southerly side of the channel to be- 

 yond the end of the north jetty and the bar is 1800 feet beyond 

 the end of the work. The crossing is north of the jetty which 

 extends straight out from high water mark. In the writer's opinion, 

 had the south jetty been built first the north one could have been 

 greatly shortened, or possibly omitted altogether. 



The low tide jetty at the mouth of the Columbia river, to which 

 reference is made, although placed on the windward side of the chan- 

 nel with reference to the littoral drift, was not built high enough to 

 intercept that movement, neither was it curved in the right direc- 

 tion to control the ebb reaction, and hence it followed that during 

 the time while the groin was filling the bar deepened, but as soon 

 as this was accomplished and the drift could travel over it, the bar 

 again retrograded and a further extension of over four miles is 

 required to catch up with the advancing bar. This jetty has cost 

 $1,965,022.76. 



The last annual report (1900) says, " The result of the survey 

 shows a decrease in depth of from four to five feet at mean low 

 water. The greatest depth reported the previous year was twenty- 

 eight feet Rapid extensions of the jetty seem essential to 



recovering former depths." The map shows twenty-three feet on 

 the bar. 1 The estimate for forty feet is placed at $2,531,140. It 

 is not an illustration, however, of a jetty placed to leeward of the 

 channel, neither is it a correct application of one to windward, as 

 it violates the conditions of protecting the channel from the drift 

 and of conserving the energy of the effluent stream. 



Failure fully to comprehend the lessons furnished by the pre- 

 cedents referred to in this report results in a repetition of the 



1 Natural depths of twenty-eight feet were reported prior to 1850. Vide Wilkes' 

 Western America, 1 849, Library of Congress. 



