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

Il
opposite shore from abrasion. Each wing dam
should be provided at its head with a low train
ing wall about five hundred feet long, parallel
When two adjoining spurs are too far apart.
It Is proposed to mark the margin of the deep
water way by detached length Of training
wall with a short spnr in rear, not connected
with the shore To promote the deposit of
able places.
In all cases the heads of ietties should be
Kept very low, and the crown should rise at
very gentle slope towards the high shore ends,
as already described.
| 1t is expected that, between the heads of
every pair OF wing dams, the bed will he deep
ened by scour to a greater depth than re-
CURED, forming in fact secondary pools, over
| tapping the heads of these works for some dis
lance in the direction of the channel while
gradually diminishing in depth. 1t is not
thought to be necessary that the ends Of these
| pools, where they are reduced to the desired
| minimum low-water depth of about II feet
| should actually or at once join the ends of sim
liar depth OF the large or primary pools al
| ready existing, by the direct action of the wing
| dams alone. The work of Joining the second.
| airy pools with the primary ones may be left
70 the river Itself by gradually more or less
| nlllng up the intervals between the spurs and
| thus reducing the area of the waterway above
and below them.
The location of the wing-dams designed for
| the improvement of the north channel, shown
| on the chart sent with Captain Green's report
| are considered to be approximate only, and
| subject to modification; but thew furnish a
/ L0OuglB
| that the desired end can be obtained without
| giving the works in each case the full length
| indicated on the chart.
| As an illustration of the probable effects of
| the wing dams if constructed as suggested,
| the spurs numbered six and twenty-five which
| appear to be judiciously located about eight
hundred yards below Spirit Island, win be
/ briefly considered. It is not the intention.
| however, to present a lengthy discussion of
the theories bearing upon this subject
| When the north channel was gagged some
4 a On ha 7scobo 81,
| ebbtide, in the principal waterway between
| Spirit Island and the north Shore was found to
be $500 cub'c feet per second 4; in the shslow
/ channel south of Spirit Island 1870 cubic feet
/ The aggregate ebb volume that passes through
| the transverse profile where the two wing
! dams spoken of are to be built, may, therefore,
| be estimated at 40, 40 cubic feet per second.
| An examination of detailed charts has fur
nished the following data for this proAe
| AreG Of Hydraulic
/ Al low tide .26, 079 50. fr. 3.642 it. ZIG IT
At half tide. 81, $50 SO. it. 1851 #. 1918 IT.
By examining the most recent detailed
| charts of the north channel it is found that at
| the ends of the existing pools the points Of
| 1915 or II feet depth are quite uniformly from
500 to 1000 feet from the 2l-foot curves of the
pools.
1t may be expected that the wing dams will
| bring about similar results and that they will
| create sufficient depths for great distance
above and below them. The low training walls
| at the heads are designed not only as guides to
| the current but also TO push out still further
the deep pockets arti1eialy formed. The
| gradual accumulation of deposited material
| and the building out of the old shore lines be-
tween the wing dams, will, it is hoped, finish
| the work.
1t must also be borne in mind that every inch
| permanently gained in depth will augment the
volume OF the flood tide ascending the river
and will produce stronger ebb currents
The closing Of the lateral channels below
Elba Island by high dams will soon be under
way. The irregularities produced In the north
enamel by these secondary water ways will
then cease, and the cost Of the works proposed
IN the present project will probably be re-
duced thereby, although it would be neither |
practicable nor safe to attempt to form an esti-
mate OF the saving that may be effected.
In making an estimate of the probable cost |
Of improving, In the manner described. the |
| north channel from the head of Elba Island to |
| the lower end of Jones Island, it has been as
sumed that on the north side eight wing dams |
of an aggregate length of about s, 900 feet with
low training walls at their heads, aggregating |
3,40o feet in length. will be constructed. also
detached piece Of training wall of 500 feet |
length opposite the central portion Of Elba |
Island. On the south side six spurs are as
sumed to be built of total length of 900 feet,
with about 1,7OJ feet of training wall. The |
total cost of these works is estimated at $780, |
0C0. The longest Of the wing dams would be |
located at the southeast point Of Jones Island; |
it will extend about 1850 feet in a southerly |
direction toward Long Island, and from its |
head will spring a training wall extending |
eastward. and to be mentioned further on.
IMPROVEMENT OF SAVANNAH RIVER FROM THE
LOWER END OF JONES ISLAND TO TYBEE ROADS, |
No work has yet been done for improving |
this section of the river beyond the opening of |
a new channel through the shoaI northeast of |
Fort Pulaski by dredging and the removal of |
wrecks and dredging on the Oyster Bed shoal, |
north of Cockspur Island. 1t is necessary to |
cause larger volume of water to flow through |
this passage The eastern continuation of his |
channel that leads into Tybee Roads, known as |
Saint Michaels ehanrel. is also subject to /
shoaling from sand driven in on the north side |
by the currents from Catalogue Sound snd bv
breaking waves rolled in by northeasterly |
gales.
The probability that the discharge into Tvbee
Roads will have to be controlled or directed in
some degree by suitable works was recognized |
in the supplementary project of March 10 |
1879, but no estimate OF the cost of such works |
was therein submitted. 1t was said that sim
pie sill jetty or low training wall rising from
to feet from the bottom, and running fr-ro |
point at or near the lower end of Ianes TSIand |
to the Oyster Bed beacon Ired light. and per. |
haps short diSSttance beyond, would doubtless
suffice.
Such a work seems to bs rather preferable to
the long lefty suggested by Captain Greene to
be run from Turtle Island to Oyster Bed ShoaI
and marked No. 81 on the accompanying chart
which is apparently designed to prevent in a |
measure, the waters of the estuary between !
Jones and Turtle islands, and Just south of |
these islands, from flowing out eastward and |
10 compel them TO increase the flow in the |
Cockspur Island channel. It's beneficial effect |
does not appear to be evident as that of the
lefty or training wall from the lower end of
vices at the mouth of the river similar TO those |
to be rendered several miles above by she letty
now in course of construction from Fig Island
and designed to protect and improve the new
channel at 'sthe Wrecks"
The jetty from Jones Island would begin at
or near the outer end Of the long wing dam at
run 10 an easterly direction to the vicinity of
Red Light Beacon ADD the quarantine station,
having length of about 10,O0O feet
The more elevated portion of OYSTER Bed
Shoal would form a natural continuation Of
this jetty, which would then be extended stUl
further eastward for the protection of St
these works is about 0O0 feet and it is
thought that they can be built at the rate of
50 per linear foot if they are about feet high
Their construction WILL therefore cost about |
$40 900, and this sum may be adopted for the
estimate, whether the work runs from Jones |
Island or from Turtle Island, the selection of a
location for the line of works being left opep |
for the present.
None of the wing dams or training walls in
tended for the improvement of this seward |
portion of the river and shown on Cant |
Greene's chart are recommended as strictly |
necessary at the present time, and may per
haps not he required at all, with the exception
of one or two spurs from Cockspur Island |
which would be useful and effective for con, |
centrating currents on the shoals south of Red
Light Beacon.
The aggregate length of these spurs is about
1,5OO feet, and their probable cost is estimated
at $4,000
SHORE PROJECTIONS.
The places where the banks will probably
abrasion or undermining are shown
thereon numbers Is, 81. IS and 81. An esti-
mate of the probable cost of this class of i'm
provements was embodied in the supplement |
tarY project of March 10, 1879. which was
thought TO be sufficient for the purpose.
DREDGING.
More or less dredging will yet be required
on the following portions of the ship channel |
below the city of Savannah:
!. The new channel at 1.-THE Wrecks"
2. The channel at the head of Elba Island
3. The shoals abreast of Elba Island upper
fats.
4. The shoals at lower end of Elba Island
DOVER fats.
5. The shoals between Jones' Island and
Long Island
6. The channel at Oyster Bed Light and fur
Their down.
It is proposed to carry on the dredging oper-
atoms in conjunction with the construction of |
the works intended to concentrate the currents
at the same places, as far as practicable, In
order that they may support each other For
merely temporary relief of commerce, dredging
will in future be resorted to in exceptional
cases only.
In the estimate of the cost of this kind of
work given in the supplementary project of
would be restricted to the places below Elba
mean low water, excavating a channel of l25
feet bottom width with side slopes of to 2.
On this basis the total cost of dredging needed
fbo baod OP ho |