Proceedings of the Polytechnic Association. 961 



engineers, and acknowledged as just by high authorities of our own. 

 country, that "the navigable condition of the channels, at the 

 entrances and ov«r the bars of tidal rivers, especially as to permanence 

 and capacity, is entirely dependant on the influx and efflux of tidal 

 water." In other words, in order to keep your channels good yoa 

 must preserve the receiving capacity of your inland basins, or tidal 

 reservoirs, so as to keep up the great inward and outward flow of 

 water to scour the channel. We acknowledge the correctness of this 

 rnle, and the necessity of adhering to it in all cases where the waters 

 of the flood tides return by the same channel and in full, to the 

 ocean, as at Boston ; but it is diflerent where the flood waters largely 

 run off in some other direction, and also cause to run oft' in that 

 other direction, a large portion of the river's natural flowage, as is 

 done in the harbor of Kew York. Every one must comprehend that 

 it is not the waters of the incoming tides, but rather the outflowing 

 waters which best clear the channel ; and that if more water comes 

 in from the ocean, than goes out, the channel is most likely to choke 

 up and be spoiled. Consequently the aim should always be to have 

 the greatest possible flowage from the harbor down to the ocean. 

 These premises being acknowledged, let us now examine the flowage 

 of waters between Xew York city and Sandy Hook, and see if all is 

 rirrht in that direction. The flood tide runs in from the ocean, and 

 up through the East river to Long Island sound, occupying about six 

 hours. Then comes the ebb tide returning .from the sound, through the 

 same channels, to Sandy Hook and the ocean, also occupying about six. 

 hours. So far all may be well:; and, if we had no Hudson river, the 

 rule laid down by European authorities might be perfectly applicable 

 to our harbor ; but we have a Hudson river, a deep flowing river, , 

 and one which makes that rule decidedly inapplicable, while tlie-. 

 East river remains open as now. The peculiar manner in wliieh 

 the flowing waters of the Hudson river aflects our channels 

 seems not to have been noticed by the coast survey, or the har- 

 bor commissioners, and never to have attracted that attention 

 heretofore which its importance evidently deserves. Indeed tliis 

 writer has found no mention of it previous to his own obsei'va- 

 tions in that direction, and remarks upon it about a .year ago. 

 During all ebb tides the water of the Hudson river flo-ws naturally 

 down to the ocean, passing off with the receding ocean watei-sin the 

 six hours or: so of ebb tides.; but on the flood tides an irregularity is 

 discovered. The waters do not then run up the rivery.abova the, city, 

 [Inst.] 61 



