210 HAUPT—DEEPER NAVIGABLE CHANNELS. [April 2, 
snow- or a sand-fence must be placed to ‘‘ windward ’’ to protect a 
rail- or wagon-way. 
It must be curved, concave to the effluent currents, to develop a 
continuous reaction, and should be constructed inward from the 
outward slope of the bar, to avoid the advance of the crest and to 
utilize the force of gravity in cutting shoreward and downward, 
instead of seaward and upward. These are some of the conditions 
which give promise of the greatest results attainable at a given 
location. Taking now a few typical illustrations of the several 
methods in vogue, it is seen that the New York entrance is to be 
deepened by dredging some 42,000,000 cubic yards from the bar, 
beginning at the easterly end of Ambrose Channel, at a cost of 
about $4,000,000, but with no definite time limit. 
Although this sector of the bar shows a remarkable degree of 
permanency, it can hardly be expected that the formation of this 
deep cut, created by artificial means in the open sea, at a point 
where the natural depths are steadily maintained at from sixteen to 
eighteen feet, will long remain open. If it be assumed that normal 
conditions would be restored, say, in a period of ten years, it would 
represent an annual accretion of about 4,000,000 cubic yards to be 
removed by dredging, which at the present price would cost $360,- 
000, or the interest at three per cent. on $12,000,000. Fora much 
smaller sum it would be possible to train the currents through this 
new and shorter channel by permanent works which would main- 
tain it and at the same time become a valuable aid to navigation. 
The effects of the submerged jetty type is best seen at Charles- 
ton, where the littoral drift is southward. Here the outer ends of 
the jetties are raised above high water, but the shore flanks are far 
below the surface, to admit the tides freely. The result is that the 
beach sand travels across them and forms shoals within the har- 
bor, while it also travels around the outer end and maintains a bar 
in the open sea more than half a mile beyond the works, through 
which the channel must be maintained by dredging. 
At Galveston, where the submerged plan was modified to reach 
above high water, the building out of the south jetty first has caused 
the bar to advance some three miles, adding that length to each of 
the jetties, which are 7ooo feet apart, and a new bar is forming 
across the mouth in the lee of the north jetty. The channel must 
also be maintained by dredging. 
At the mouth of a sedimentary river, like the Mississippi, where 
