The St. Louis Republic., 1903-12-31

Three distinguished attendants Mt til
meeting of the American Association fc
the Advancement of Science. Mr.. Wrigi
is United States Labor Commissioned
Professor Sanderson occupies the cha
of entomology at the Agricultural Co
lege of Texas, and Doctor Howard
Chief of the Bureau of Entomology {
Washington.
of the Mississippi will occasion deposits
in its channel, ard eventually elevate
rather than depress the surface OF the
river. In support of this opinion they
have urged, first; that actual measure
ments upon the river at certain crevasses
prove that deposits are made when the
velocity is thus checked: and. second, that
theoretical reasoning indicates that such
deposits ought to be anticipated.
Certain operations OF this survey were
conducted with especial reference 10 de-
terInine the effects OF outlets. and they
demonstrate, with degree of certainty
tons. that the opinions advanced by these
writer's are totally erroneous
The report then analyzcs the two cases
cited in proof of the assertion, viz, the
Fortier crevasse- of April, 1919, and that
of Bonnet-Carre of 1850 and shows that
the phenomena attributed TO the breaches
were those ordinarily found 10 result from
bends and straight reaches. and that. in
fact, even in natural crevasse there
was no bar formed below such opening, in
the banks, and that the assertions TO the
contrary are erroneous They add: There
is no evidence whatever that any filing
up of the bed ever did occur in conse-
quence of a high-water outlet, and. more
over, 1t is impossible that il ever should
occur. either from the deposition of sedi-
Ia2nt held in suspension or drifting along
tie bottom.
-, - The conclusion is. then, inevitable
that so far rs the river itself is con-
cerDed they are Of great utility Few
solution.
Perhaps the best evidence on this
nuch-mooted point will be found in the
answer OF Nature herself. so that an ex-
animation of the bed below the head of
the distributaries will throw much light
on the subject.
REVERSE CURVES.
Taking that portion of the delta below
the forts which is in a state of nature and
unleveed it is observed that in the re-
verse curves swing around these defenses
where the radii are but two and one and
ohe-haH miles, the greatest depths are
tnirty-one and twenty-nine fathoms re-
spectvely, due to the reaction OF the
sharp concave banks and the reduced
width. AS the radius iengthens to three
niles, the thaiweg depths shoal to
thlrteen, twelve and eleven fathoms. and
nne,. 1he river also widens gradually to the
the width exceeds n half mile and the
depths increase to sixteen fathoms abreast
OF the opening and to thirty-ninc fathoms
ana no bottom al quarter of a mile
lower down, with over fifteen fathons for
several m.les
In this instance. therefore. the depth
peioW the cTevasse instead of being les
IS more than twice as great and 1t Is not
que 10 local curvature, but apparently 10
impact due TO the suction or set OF the
currents toward the right bank.
Continuing downstream. as it widens
m In 1r-s. Ift
to about six fathoTns at the head of the
Passes which may be regarded as three
eTevasSes and yet 1t Will be found that
depths exceed those of the undivided
stream. In the Pass n Loutre it is twelve,
n South Pass ten and in Southwest Pas;
thirteen fathoms. with no bottom, all at
the points of incidence of the divided cur
rents. Again in the Pass a Loutre at the
cravasse, which formed in 1891, the depth
abreast the opening is thirteen fathoms
ana one mile below it is fourteen and one
hai1 This same stream again divides in
10 Two min branches. sh wang eight and
one-Guarter fathoms below the point of
separation, in the more direct channel
and eleven and one-haif along the sharper
concly:ty of the Southeast Pass. due to
reaction OF the bank. Without further
elaboration, the same general results may
pe seen wherever a crevasse occurs and
there is no indication of shoaling due to
the escape OF the excess of the flood
waters or loss of volume
ON the other hand. there is very
marked benefit observable in the relief af-
forGed to the stream. for these openings
enable il to discharge large portion of
Its sediment beyond the banks and out of
the highway of commerce. which must
otherwise be carried to the Gulf and be
dropped directly across the channel, thus
extending the trough. reducing the slope
and increasing the height OF the floods.
In fact a former Chief Engineer of the
State of Louisiana stated that the reason
for selecting the southwest Pass for i'm
proyement was because of its greater
general depth: so that the shoaling, which
channel four miles by the two jetties.
would not so soon affect the navigable
depths. in copsequence of the contraction
of the outlcG.
.'As aiready stated. similar results have
taken place in the South Pass above the
jetties where the fill in one place has ex-
ceeded fourty feet. But these la.erai out
let's also play an important part in the
reclamation of land as well as in Teduc-
ing foods and improving navigation. for
by this method of hydraulic grading. with
and converted into valuable plantations.
The extent of these deposits may be
roughly determined by a comparison of
the United States Coast Survey charts Of
1854 and 1884. from which it appears that
the accretion 10 the land above water in
the vicinity OF the Bayou Grand Lard,
Spanish Pass. Red Pass, Tiger Pass,
Grand and Williams Pass. during the
thirty years between the surveys. amount
ed to about 1i3 square miles or nearly 49,
000 acres. At Cubitt's Gap, where the
river Is straight and wide. the rate of
deposit has also been considerable. This
breach occurred IN 1862 and within few
years an area of about eight square miles
was raised above water. while survey
made by Mr. Chucas Lewis. I'm 1892
showed further deposits covering some
g square miles. which is already laid out
on paner under the Government land sys-
TEN, into townships and sections.
COST CONSIDERATION.
"a better idea of the extent of this con-
| button to the wealth of the nation may
be obtained by computing the cost of Sc
| curing IT by the usual method of bacA-
filling by the use Of hydraulic dredging at,
say, 10 cents per cubic yard, and assum-
ing the average depth TO be nine feet On
this basis the total fill would aggrsg1-e p
some 4OaO0Dc00 cubic yards in the thirty
years, or over 13,91,Go0 cubic yards per
year. The total cost OF securing this re-
suit by dredging, regardless OF iIiile, would
therefore represent si0.0oo.oo0 for this one
crevasse.
.At the Jump where 113 square miles
were reclaimed in about thirty years, the
cost would have been s3.530.o01 per annum
IL attempted by mechanical dredging. or
Si05. coo t00 for the entire time (or over $3.50
per acre.. 90 that the cost would have
been n-ohibitory. This one annual depos-
1t withdrawn from the-riyer averaged
total amount of sediment carried to the
Gulf has been e-dmated by Humphreys