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


These three wing dams will cost about S25 coo.
The cost of improving the river in front OF
the city is therefore estimated at $l95,OO0 viz:
Amount of claims for damages. ....... SIS 600
Excavation and dredging. ............. $4,000
Three wing dams from Hutchinson's
1Slaho. OBSERVATION-DISCLOSURES. 29,UUU
Total. Observation-Disclosures. $19s, 900
NEW CHANNEL AT THE WRECKS
Experience having shown that the new chan
mel at the Wrecks" running close to the
south shore as the river energies from the con
fines of Fig Island, cannot sufficiently main
tain the depths obtained by repeated dredg-
ing, it was considered eXpedient to begin the
construction of a work, the ultimate necessity
of which has been indicated in several preced-
ing annual reports. but had been temporarily
held in allegiance. The work referred to is a
DETECTING jetty. or training-wall, extending
eastward from the lower end of Fig Island On
my recommendation the design for its con-
struction was approved by department letter
dated November 4, 1881.
The jetty, if carried up to a height Of or 81
feet above the level of low water, will keep to-
eether the currents issuing from Front river
during the latter steges Of the ebb-t tide,
and may safely be expected to exert
a very beneficial influence on the preservation
of such depths as will be gained by dredging,
and even to deepen the channel by its own
action. especially when the dam at Cross Tides
shall have been built up to the height suggest
ed in this report.
The total length Of the jetty, as now design
ed, is {, 200 feet 1t is built Of log mattresses,
Overlaid with brush and riprap stone. Above
the lOwwater line the latter material will be
used literally. The bottom course is already
laid for length OF 2C40 feet, and a second
course for length Of 800 feet. and the work
will soon be carried up to the height Of two or
three feet above lOW-Water mark on the entire
length designed. If built up to the level of
half-tide, except on the lower end, for length
OF about 200 feet which may gradually drop
down to height of about three feet above the
had n a froFI HI
at that point, the cost Of this work is estimated
at $4,000.
IMPROVEMENT OF THE WATER WAY FROM The VI
CINITY OF FORT JACKSON TO THE HEAD OF THE
NORTH CHANNEL
The distance from the lower end of the Fig
Island jetty, here referred to. to Fort jackson,
on the south shore of the Savannah river. is
about half mile, and from that place to the
head Of the north channel two miles.
Down to near the upper end Of the south
channel, one mile below the fort, the naviga-
bic channel passes near the south shore, which
is slightly concave, and ample depths are
found here. But on the reach abreast the head
of Elba Island, of about one mile in length
part of which is known as THE DISTINCTIONS -
he depths are much reduced below the stan
dard desired. Through this reach the main
channel passes from the Georgia to the South
Carolina shore. Occasional dredging has given
here but temporary relief as is generally the
case where an infection Of river is to be dealt
with
IL Is Unnecessary " uAEcCJ stronger currents over
these shallow places, and this can be effected
by contracting the water way. The wing dams
proposed by Capt Greene are well located for
the purpose. 1t appears, however, that only
those numbered Is, II and 10 on the chart
sent with his report are Immediately necessa-
ry, as they will act directly upon the portion Of
the river to be improved. Possibly No 10
might be included, as it will produce an extern
sion OF the deep water pocket now ending op-
pOste the head of the south channel into the
defective reach; and also dams Nos, 5 and liz.
closing the channels, on the northwest and
southeast side Of Barnwell Island.
The other spurs above No. 49, to-wit Nos g.
z 9, and II, shown on the chart, are evidently
designed TO concentrate the outgoing waters
Of Back river, and guide its ebb-curreHts at a
favorable angle into the main channel near
Fort Jackson. They would undoubtedly assist
in creating greater depths in the vicinity of
''the distractions" but their construction
does not seem 70 De OF very pressing need, and
should be postponed until demonstrated to he
necessary.
In relation to this matter, the question may
be raised whether it will be more advantageous
to effect. Just below the Fig Island ietty, nv
suitable works and at a favorable angle the
junction or the ebb-curTents from Back river
and Front river, or to promote the entrance of
the food-tide into Front river, and slightly OBJ
struct us now lnic Back river, through extend
ing the Fig Island jetty by sill-danl in an cas-
terry direction to the low islands opposite Fort
Jackson. A low dam arranged as here suggest
ed, though only about three feet high above the
flood tide currents into Front river, and would
in measure, act as submerged training-wall
for the waters flowing out during ebb-tide.
Such sill=dam would have length of about
$500 feet, and with base of 80 feet width
would cost about so, coo. The works proposed
by Captain Greene, comprising Nos. 3, Z 8 and
II, and three spurs on the north side Of the
Fig Island jetty, would have an aggregate
length of about 1900 feet, and will probably
cost, approximately, $4,000
1t 1t thought sufficient to include in the new
project the two closure dams at Barnwell ISL
and, and those wing dams that are undoubted
" required to improve the ship channel at the
Constructions" and vicinity. They will be four
in number, by including No. Is, of an aggre
gate length of about 1900 feet AS a general
rule, the height of the shore ends of these spurs
may be about feet above mean low water for
a length of 100 feet. For the following 200 feet
OF length the crest may gradually drop to a
height Of feet above low water level, from
which point it may run out at gentle slope TO
the head Of the work next to the channel
where it may not be higher than feet above
the bed Of the river. This will prevent the
formation of deep holes caused by eddying
currents at the head, and the deepening effects
of the spur will be more evenly distributed
over the width of the channel In all cases the
head is recommended to be In the shape of a
T, to form a low training wall of from 800 to
500 feet in length, to extend the effect of the
spur some distance above and below. 1t will
also obstruct the currents that are generally
found to run along the sides of wing dams to-
wards the channel, and will, moreover in some
measure, prevent the sediment which is drop
ped at intervals between the spurs from being
washed into the channel.
The elevation of the crown above the bed at
the different points OF the wing-dam may of
course. vary from the rule here sugg ested. but
1t is believed that with longitudinal profile
approximately like that described, the desired
effects will be realized, and the estimates have
been made on that basis. AS to the mode of
construction, it is assumed that the crown will
be uniformly feet wide. with slopes of TO
on each side. ALI that portion of the dam
from to 2 feet above mean low water is pre-
sumed TO be of riprap stone; below, alternate
courses or log or brush mattresses and stone,
the latter used as sparingly as practicable. The
bottom mattress is supposed to protect about
feet beyond the foot Of the slope on each side
of the dam.
At present prices it is estimated that the four
wing damS designed for the improvement Of
the channel abreast Of the head of Elba Island
together with the Barnwell Island dams will
cost, approximately, $4,000,
DAM AT THE HEAD OF SOUTH CHANNEL.
This work forms part OF the supplement
tary project of March 49, 1879. 1t was designed
to increase the volume Of cob flow in the north
channel. and was intended to be submerged
dam, keeping a portion of it. for width Of
two hundred feet, at least ten feet below mean
low water for the accommodation or vessels
Of moderate drsught bound in or out OF st
Augustine creek. which forms part of the In
land passage to Florida
Operations were commenced here some time
ago, ana at the emo OF Juo past fiscal year an
apron, or bottom course of mattresses of
"a feet width and IS inches in average thick
ness, overlaid with some riprap stone
had been laid from the line Of
high water on ore bank, across the
river, to the corresponding line on the other
bank. A second and third course OF narrow
mattresses cover portions Of the apron.
The original width of the transverse profile
of the south channel at the site of the dam was
1000 feet at mean low water and 400 feet at
high water. with an average low water depth
of 10 8 feet and maximum depth of 20 feet.
The works thus far executed have reduced
these dimensions somewhat. The widths of
now 900 and .O6O feet respectively; the average
low water depth is 1914 feet and the maximum
depth is 1875 feet. The area of cross section
has been reduced from IL, $50 square feet TO
9,950 at low water. and from 81, $50 square feet
to 1000 at high water.
1t appears necessary to raise the dam higher
to produce appreciate effects It is proposed
to reduce the average low water depth to about
five feet, and perhaps still more, leaving gap
as originally designed
An estimate OF the probable cost of this
work is given in the project of March 19, 1879.
and Is judged to be ample even il the dam is
raised higher as above indicated.
IMPROVEMENT OF THE WATER WAY OF THE NORTH
CHANNEL FROM THE HEAD OF ELBA ISLAND TO
THE LOWER END OF JONES ISLAND.
The length of the present ship channel in the
several reaches embraced in this section or the
river is about 616 statute miles. Three COM
paratiyely deep pools, with low-water depths
from II feet upwards, are found here, OF an
aggregate length of about three miles. The
upper and lower pools are located on the north
or South Carolina shore of the river; the mid
die one on the south shore near the lowerpart
OF Elba Island. The shoaI reaches occupy the
1ln foahninaiIv known a q fn4fapfinnQ n