34 ( [Dee. 16, 
Haupt. ] 
lines as proposed, there will still be the serious violation of the 
first of the above established principles, and the further serious 
objection of directing this diminished tidal prism into the 
face of the flood, near its point of maximum energy, with noth- 
ing to lower the plane of tidal scour except the small amount 
of head due to contraction. This is in violation of the accepted 
rule that all works designed for river or harbor improvements 
should aid, rather than oppose, nature. To turn an ebb stream 
out of its natural bed and deflect it by jetties across a bar is 
to impose additional resistance ; first, from the change of 
direction, and second, from the additional resistance opposed 
by the higher crest and steeper slope of the bar. There is also 
a less effective relative area of ingress due to the form of the 
converging jetties. 
Unless there is a large augmentation of the tidal prism by 
land drainage or from some other source during the epoch of 
the flood, such works will not, in general, prove beneficial. 
The location of the mouth of the jetties and the general de- 
sign of the works is evidence that the principles enunciated 
in this paper as to the action of the flood and ebb forces have 
not been, as yet, fully appreciated in the planning of works 
of this description. The South Pass jetties are subjected to 
totally different conditions, as the flood tide furnishes but a 
very small percentage of the ebb discharge. 
GENERAL REQUIREMENTS FOR HARBOR IMPROVEMENTS. 
From what has already been presented as to the origin of 
the barsand the relations that exist between the flood and ebb 
resultants, it must be evident that the engineer who proposes 
to aid nature must so design his external works as to prevent 
the flood tide from carrying sand into the channel to obstruct 
