The New Orleans daily Democrat. [volume] (New Orleans, La.) 1877-1880, 1877-07-03
THE SOUTH PASS.
OPTICAL REPORT OF CHIEF EN-
GINEER RADs.
Grand Summary OF Results ana DemSm-
strafed Success 0f the Enterprise.

sT. LOUIS. June 2s, 1877.
julius .. Walsh, Esq., President South Pass
Jetty Company:
Sri have the honor 10 submit ths following
report upon the improvement OF the South Pass
Of the Mississippi river:
HEAD pr pAss.
The depth on the shoal in the river obstruotinp
Flow water when the jettiss at the mouth were
begun. Until late in October OF 1876, this shosl
| renamed almost intact, while the channel be-
| tween the istties, twelve miles distant, hsd
rapidly improved; and although twenty feet Of
water could be carried ont OF the pass TO sea,
| this was not available for commerce because OF
| the shoal obstructing the entrance at its head.
70 create channel through this shoal an addi-
tionai system of works was designed and con-
| structed at the head OF the pass, including two
| submerged mattress sills two feet thick, seventy
feet wide, and each over 5000 feet long These
were sunk on the bottom OF the river across tho
entrances TO Southwest Pass and Pass-a pOutre.
The South Pass discharges only about one-tenth
OF the entire volume flowing out oil the three
passes, and these sills we're designed to prevent
any enlargement Of the two great passes, and
thus hasten the securing action on the bottom OF
the new channel 10 South Pass. They are laid in
deep water, and thirty feet OF depth can be oar
riet intn both passes over them. They are well
ballasted with stone, and soundings show that
the bottom OF the river is level with the tops
OF the sills. They will therefore, be likely 10 re-
main permanently In their present position.
These stills diminish the entrances into these two
great passes about 7OU0 square feet each.
THE WORKS AT THE PASS
actually embrace and control the entire afschsrae
OF the Mississippi river, which is at this point
one mile and threequarsers wide. They, there
iore, ia snrpass IN msgnitude any similar works In
trance TO South Pass has been permanently con-
yerted into narrower and parallel one OF $50
ieet in width With the exception Of tbs east
dyke, they were commenced after the food OF
1876 had begun to subsids, and in October had
80 FAR progresse 40 TO control the flow into the
pass. The use Of dredgeboatg was then resorted
to on thu centre line between the paraeied piers
within which the new channel has been formed
TO hasten it's development. These succeeded in
cutting. narrow channel OF about 20 feet In
depth through the shoal; but owing TO the ex-
ceptionaly low stage OF the river st this time the
current was 80 feeble that bat little impression
was made by the river through this dredged cut.
and On the lss OF February it was not sufi hentiy
widened TO be available for vessels drawing over
Is or 16 feet.
As the present depth OF the bar at the mouth
10 no greater than " was when the works at the
nead were conpieteds nor indeed as great, the
cause which interrIs,ssd the deepening that had
previously proceedTs-,vith such remarkable reg
ularity between the jesties. yili be fnllv under.
stood when the effect Of the works at the head
Before the works there we're built the width.
on the crest Of the shoal OF the volume OF wa
ter flowing into South Pass meaured transverseiy
10 the current was 240O feet. A concentration Of
this volume between parallel piers only $50 feet
apart Was relied on to secure the requisite depth
OF channel through tie shoal, but this concentrs-
tion las will be seen by q chart OF the worksl
could only be obtained by the erection OF dams
and piers which greatly diminished the low into
TO the pass, and thus, for the time being. com-
pietely suspended the erosive action OF the cur
rent between the jetties, twelve miles below
them,
During November, December and Janusry.
last, owing to the extremely low stage OF the
river, We were not justified in expecting scpur
through the works at the head OF the pass but
were prepared to find deposits In the D sss, and
also between the jetties. To rob the pass even
Of so large portion of its water Az
was for the tme barred out by our works at the
head necessarily reduced it's current and caused
considerable deposits to be thrown down during
The time 80 much water was excluded.
Under these circumstances the rise In the river
WAS looked for with considerable anxiety. re
occurred about the 1st Of February, and as was
expected, soon caused rapid enlargement OF tho
channel through the shoal that had for so MANY
years obstructed the entrance into the pass.
seventy thousand cubic yards OF sand were ex-
cavated by the current during the first seven
days OF February. Since that date, as the charts
sent to you from time to time show, the enlarge
ment OF the channel through the shoaI has been
going on with great rapidity, and upwards OF
45O, 600 cubic yards have been excavated from IL
up to the present time.
The following table gives in detail the progress
of its enlargement TO May %, 1877:
Least width Least width