Savannah morning news. [volume] (Savannah) 1868-1887, 1882-03-03

dam at the cross tides much higher than it now
Is. 70 contract the waterway or the north
channel below Spirit Island, and to protect
Saint Michael's channel below Tybee Knoll by
training wall. They differ in regard to the
treatment Of the reach Of the river from below
the rig Island Jetty, recently approved BY the
Chief or Engineers and now in course OF con-
struction to the head Of Elba Island
Captain Greene proposes TO guide the
navigable channel on its north side by q
series OF spurs, while Mr.. Fremont would
throw low dam across the lower entrance Of
BACK river. It is TO be regretted that the dams
intended TO close the side channel below Elba
Island have not yet been constructed, owing
TO the utter failure Of the contractor to accom-
plish anything. His contract was annulled on
May l9. 1881, aud the preparations for doing
the work by hired labor with material bought
in open market, and for procuring the requi-
site plant, consumed so much time that actual
operations could not be commenced until re-
Gently. If these dams had been finished, and
the submerged dam across the south channel
at the head OF Elba Island been raised some
what higher, the observed effects of these
works would have furnished valuable infoT
nation in regard to the quesrion'of what may
be needed for further and permanent i'm.
provement of the lower Savannah river.
There can be no doubt. however. that the
water way of the north channel should be con-
tracted where it evidently is too wide and the
real question is the number and extent of the
works to be constructed. the sites for which
are indicated in general way by the river it
self.
A radical solution of the problem would con-
sist in combining the river between tralningwalls
or bulkheads all the way down to Tybea Roads
increasing the space between them in an
preaching the lower end. This was the latest
form according to which the river Clyde was
improved; and the river Mass. from above
Rotterdam to its outlet into the North Sea was
similarly treated. By such an arrangement the
currents of the ebb and flood tide would be
compelled to follow the same channel. and
the result wouli be the maintenance of a
nav1gable water way OF ample depths The
expense would be very great, however even
II the training walls were carried up to the
level OF half tide only. as in the case Of the
river Mas, and further discussion of such a
project appears to be premature at the pres
ent time.
A more economical method of improv-
where it is too wide and of insufficient depth is
offered by the employment of wing dams or
spur Jetties. BY proper disposition of such
works it is believed that without excessive
cost, permanent channel may be established
OF sufficient depth to enable vessels of % feet
draught to pass from Tybee Roads to the CITY
on the Hood tide. which is the maximum
draught contemplated in the project previous
lY submitted for the Improvement of this tidal
stream. No greater draught than this can be
safely carried over the Tybee bar except on the
hgh water or spring tides, and not even then
unless the sea is more than ordinarily calm
IL is well known that the first real improve
ment of the river Clyde was obtained by means
OF number OF rubble spurs, which were built
Dy john GOlOOrno IN the years from 1913 to
1915, and aided by dredging on the hard shoals
Where, in 1869, only two feet depth of water
at low tide had existed, these works had in
100. created channel of 300 feet width and
six feet ten inches depth, which, at the end of
the rext six years, according to Mr. Golborne's
statement, had increased to twelve or fourteen
rect, while the spaces between many of the let
ties had become filled UP and covered with
grass. great number of additional jetties
were built at the beginning of the present CEN
fury, by the advice of John Rennie who also
recommended TO connect the heads of the
spurs by continuous low rubble walls which is
believed to be the first instance of the adoption
or the system 0floBgtudinal training walls
In regard TO the question of the number
ana size OF the works needed for contracting
the RIVER, the Following remarks are offered:
The channel way Of the Savannah river like
that OF most other rivers in their natural con
dltlsn, presents succession Of extended and
comparatively deep pools, separated by reaches
OF shoal water. 1t would seem that the more
economical plan Of improvement will be to
construct works in the shoal sections of the
river designed to produce channels of adequate
cepth and OF sufficient length to connect the
deep pools. 1t is obvious that this method
naturally leads to the preservation Of the pre-
sent line OF channel, to which there seems TO
be no special objection. 1t is trIe that the
channel is somewhat crooked, but the curves
have large radii and, so far as known have
never been considered as an inpedimept 10
navigation. To attempt to straighten the chan
mel would throw some of the works irto the
deepest water and render them more exaen-
Sive ltmay be said, also, that the causes which
tend to throw the main current Of river alter
nate!y from one bank TO the other are general
ly rather obscure, and it seems advise HE in
the present case to accommodate the works TO
the natural course Of the main current, where
it is practicable. instead Of attempting to
change it violently.
The deepest pool is found at the hesd Of the
north channel, between Spirit Island and the
shore Of South Carolina At the uarrOwest
part, at low water. the width is 055 feet, with
q n1n hrVH lie IN
maximum depths of from IS to 40 feet AZ
mean low tide. The 1s-foot curve or pocket
commences at point above Spirit Island and
ends opposite the lower end Of that island its
length being about 900 feet
At the easterly end Of Split Island the north
channel wideus to 500 feet, with a hydraulic
radius OF II % feet at low water The deep
water channel of this profile is about SEQ feet
Wl1e, with depths varying from IL to 171k feet
This may be considered, approximately as a
standard profile, representing cross section
OF the river as it should be when improved as
proposed.
Passing below the confines Of Spirit Island the
river rapidly widens; three-quarters Of a mile
below the width is over 1000 feet with CORE
spending shallow water. The low-water depth
OF the Davigable channel in this vicinity is
estimated at IL feet, or little over, but on
very limited width
From this point down the river gradually
narrows, and at the lower end of Elba Island
another pool is formed. The total width is
here about 2 500 feet, and in the deep water
way near the island low water depths Of 20 feet
ard upwards are found The 16-foot pocket
extends about parallel to the island shore for
a length OF about 1850 feet.
The river then again widens and at the
mouth Of the north channel between the SOUTH
easteriy point OF Jones Island and the middle
portion of Long Island, the width is about
700 feet, with available low water depths of
from 1919 to IS feet channel way. The main
current passes from Eiba Island across the
river 70 the north shore Of Jones Island. where
1t forms a third narrow pool, with depth vary
ing from IL TO 20 feet for a length of about
mile.
Along the shore of Long Island good navi.
gable channel exists, the maintenance OF
which is probably due to the slight concavity
and comparative toughness of the banks The
Iow-water depths reach up TO 20 and 81 feet:
but these depths are lost near the lower end
of the island and beyond, in consequence of
the weakening Of the ebb currents by the rapid
expansion OF the waters as they approach
Tybee Roads
The large shoal or island, partly bare even at
high water, north of Fort Pulaski known as
Oyster-Bed Shoal, divides the ship channel
into two arms, of which the southern one
since 1872 has been selected for use and has
been deepened by dredging. 1t was, and, TO
some extent, is now, obstructed by shoals and
remnants OF wrecks, and needs further inn
provement The same is the case with the
easterly continuation of this channel, from
Tybee Knoll to Tybee Roads, known as st.
Michael's Channel. where vessels sometimes
find trouble in passing.
The work Of improving the Savannah river
and harbor, so as to increase the depth Of the
water from the bar up to the city to % feet as
provided for in the act of March g. 1881. and
which is Interpreted to mean depth that will
permit vessels drawing % feet to reach the city
on the food-tide, requires not only the con
struction OF certain works in the north chan
mel but also higher up, as far as the Cross
Tides, four miles above the city
The various points where such additional
works are believed to be needed. with the pro-
hail n lie will hsa E,-so a.
discussed, beginning at the Cross-Tides.
CRossTIDEs.
The further improvement of the harbor of
Savannah and OF that portion of the river inn
mediately below the city, requires an increase
of the flow OF water in that section. For that
purpose the submerged dam at Cross-Tides,
recently constructed, must be raised. as the
strength OF the currents across lis low crest
towards Back river, during ebb tide, shows
that too large volume OF water escapes in
that direction and is lost to the Front river
1t was stated in the last annual report that
the crest of the work then reached at several
places up to the level OF low water while at
other points there was from six to eight feet Of
water over it at low tide, and that it might be-
come advisable to raise the dam ultimately
to the level of high water. In the latter event
no doubts are entertained that the work
will have beneficial influence on
and below the city, and the estimate of the
cost of further improvement should therefore
provide for that contingency.
There is a question whether gap should be
left in the dam for the passage Of river craft.
In view OF the violent currents that are now
frequently observed here, it is doubtful
whether boats could sefely, pass through the
pan when the crest of the dam on both sides
The opening shall have been raised to high
water mark. and the danger Of undermining
on the down-river side or the dam will be con-
siderable IL a channel be left through it. In
forming an estimate of the cost Of completing
tho work nm IN the level of ordinary hi0h