Haupt.] 1^-^ [Jan. 18, 



at different times and places, there would seem to be no reason why they 

 may not both be created. A fairer statement of the case would be that 

 two good channels would be better than one poor one. Apropos of the 

 amount of water escaping laterally during the ebb through the beach 

 opening in the breakwater, the Reports of the Chief of Engineers are 

 explicit m stating that it would be much less than the amount admitted 

 during flood ; and in view of the beneficial effects of the 600 feet gap in 

 the great north wall of the Dublin entrance,* there would seem to be no 

 room left for doubt as to the benefits to be conferred by such a vent as 

 that which I have proposed. The loss of energy through this lateral out- 

 let during ebb would be immaterial; as it lies close under the lee of the 

 shore, and nearly the whole of the ebb is trailed to discharge over the bur 

 at the curved outer end of the breakwater. 



In discussing the Government projects, it was originally deemed funda- 

 mental to their success that the flood tide should be admitted freely to 

 secure the necessary prism for ebb scour, and in the design for the beach 

 channel entrance, which I have given, I have provided a form that must 

 pass more flood than ebb, and hence the excess would go to increase the 

 ebb at another point of the bar. It is this difference of quantity upon 

 which I rely in part to increase the efficiency of the ebb as well as the 

 conservation of its energy over nearly one-half the crest of the bar. 

 These principles are universally accepted as sound. They certainly will 

 not fritter away the energy available for scour in an "ill-defined, uncer- 

 tain, or altogether insufficient action," but must concentrate all there is to 

 be had over the most limited as well as the weakest section of the ])ar. 



In considering the utility of high jetties for Charleston, the late General 

 Gillmore said : " The excess of ebb over flood scour is due to two causes : 

 (1) To the rainfall of the natural drainage area ; (3) To the volume of 

 water carried in over the bar by waves of translation, which afterward 

 form a part of the general outflow. High jetties, or those which rise above 

 the level of high water, will cut off all supply from this source, except 

 what little is carried in between them." * * * And he adds : "There 

 are few maritime constructions, says M. Minard, less susceptible of gen- 

 eral rules and more dependent on local influences than jetties. He might 

 have added that we are as yet unable to deal with these local influences 

 with much confidence or satisfaction." To avoid these defects of high 

 jetties the Government has tried the submerged plan with, thus far, no 

 better success. 



CONCLUSIOK OF THE BOABD. 



"In fine, the Board, after an attentive study of Prof. Haupt's paper, 

 supplemented by a personal interview, in which he was aflbrded every 

 opportunity to explain and elaborate his views, find that they are purely 

 theoretical, are unconfirmed by experience, and contain nothing not 



* See Franklin Institute Journal, for April, 1888. 



