1903.] HAUPT—DEEPER NAVIGABLE CHANNELS. 209 
tion, and not to velocity simply, might be cited, but a few must 
suffice. 
In the Thoroughfare at Longport, N. J., the landing pier has 
caused a hole forty-eight feet deep, while 800 feet away there was a 
bar bare at low water, but covered by a tidal current almost as 
swift as that past the pier. 
In the Charleston gorge the maximum depth was eighty-two 
feet, while on the bar seaward thereof the depth was zero, and 
the best crossing was six miles south of the gorge. At Fernan- 
dina (Cumberland Sound), Ga., the maximum depth at the head 
of Amelia Island, projecting into the channel, was sixty feet, and 
abreast of it bare at low water. 
The Galveston gorge shows about fifty-eight feet, while the 
normal bar depths were twelve to thirteen. The St. John’s river, 
Fla., swings to the sea through a radius of one mile, carrying a 
maximum depth of fifty and three-tenths feet, and as the axis 
straightens to a tangent the depth diminishes to twenty feet. It 
then strikes a jetty at an abrupt angle which develops its latent 
energy and scours to fifty and two-tenths feet, but as this is not 
maintained by the convex curve of the jetty, the channel deterio- 
rates to about eleven feet. 
The building of a spur in the Mississippi river at right angles to 
the bank had the effect of increasing the depth from twelve to 
nearly one hundred feet in consequence of the violent eddy which 
was created, and now that the spur is covered and the river has 
assumed a new regimen, the depth has shoaled to about thirty feet, 
which is maintained. — . 
From these few instances it would seem to be a fair inference 
‘that depths may be developed quite as well by single lines of con- 
cave directing works as by two, if proper attention is given to the 
volume of affluent as well as to the relative amount and direction 
of the motion of the bar-building materials. 
PRACTICAL SUGGESTIONS. 
In view of the requirements as previously stated, it is evident 
that to protect the proposed channel from the littoral drift a sub- 
merged low-tide or half-tide jetty will not suffice to arrest this drift, 
but it should extend above the highest tide. It must also be placed 
between the channel and the source of the prevailing drift, just as a 
