The Greenville times. [volume] (Greenville, Miss.) 1868-1917, 1890-08-23
THE MISSISSIPPI RIVER.
What Ii Needs and Why II Needs Il
Manufacturers Record. /


important and valuable of its series of
articles on Mississippi River Improve
ment, from the pen Of Capt Smith S.
Leach, United States Engineer, now To-
Gated at Boston, formerly of Memphis.
Capt. Leach was tor twelve years in
active charge Of Mississippi river i'm
provement operations, for years sec
retary Of the Mississippi River CON-
mission, and for years United States
engineer in charge OF government
work on the river between Cairo and
the mouth Of White river. He is re-
gsrded by the people of that section
as one of the ablest engineers in the
army, and by many thought to under
stand the phenomena Of the Mississippi
river better than any engineer since
the time of Capt. Eads. Capt. Leach's
paper is given below:
The popular conception of the Mis-
sissippi river is that it is simply a
stream of water; that Its channel is
nothing moro than containing vessel,
oblivious fits contents that its floods
are only the spilling out of portion
of the water at times when the vessel
is too small for its purpose, aud that the
remedy for such an overlooking river
is the same as tor an overhowing tub.
The Mississippi is stream Of water,
to be sure, but it Is very much more
than that. The water carries to sus-
pension varying but always consid-
cradle quanty Of sediment. Its chan
mel is plastic conduit, formed by the
river ITSELF and as sensitive to It's de-
mands as a mother to the cares of her
child, undergoing incessant changes in
response to the moods of the current.
These changes, so far as they affect the
capacity of the channel to do its work,
are of two kinds, one of which makes
the bed larger and is beneficial, while
the other makes 1t smaller and is detri-
mental. Both depend upon the ability
of the water, considered as a vehicle,
to carry the sediment, considered as lis
load. The vehicular power of the wa
ter is derived solely from the fact that
it Is in motion, and tho best index Of
this power Is the amount of motion as
represented in the velocity. Changes
which make the channel larger are
caused by the moving water taking up
material from the bed and carrying It
away aud arc the result of accelerated
velocity. Changes which make the
channel smaller are caused by por-
ton of the sediment In suspension be-
ing deposited on the bottom and are
the result of diminished velocity. The
conditions of the problem are so in
finitely various that no exact relation
has been or can be established between
the velocity of flowing water and its
sediment carrying power. But thous-
ands of concordant observations DEM
onstrate that no matter with what vc-
locity the river is flowing and no mat
ter what amount of sediment 1t may
be carrying, il the velocity be decrcas-
ed, some Of the sediment will be de-
posted. The converse of the propo-
sition, though equally true In the ag-
gregate, Is more subject to exception
in individual cases. A man is ever
more ready TO take one up, and can
carry a load which he could not lift,
and river may be excused for mani
Testing a like disposition. Changes
unfavorable to the efficiency of the
channel being produced with greater
falicity than those favorable, the gen.
eral tendency of the river in Its natural
condition is to deterioate.
The channel which the river now
has is the net result of its present silt
transporting power. ANY channel
which 1t may have in the future will
be the result of the same cause, and
will be better or worse than the pres
ent one accordingly as the silt-moying
power of tho stream has been increas-
ed or diminished by agencies or human
effort. In all questions Of the regimen
of this river and OF changes in 1t for
the purpose OF important, the matter
of first aud paramount Importance Ia
the effect upon the velocity, Every
scheme advanced, no matter by whom
or for what reasons, should be al once
subjected to this crucial test and made
to stand or fall by the result. ANY
plan, the result of which is to diminish
the velocity throughout section of
the channel, it is vicious and the ad-
vantages promised BY IT illusory. rlans
which tend to conserve or Increase the
velocity are beneficial and any disad-
vantages which may accompany them
will be temporary, The velocity Is the
unerring touehstone which distinguish
es the true metal Of every applicant
for favor, which discovers an enemy In
the flattoring and boastful outlet and
disclose friend in the conservative
aud commonplace leyee.
Tho escape of water from the chan
mel of The ylyer nj suy point or under
any circumstances Is accompanied by o
reduction of velocity below the s..;i. ,,c.is
of escape, and by deposits in the area
of reduced velocity, A steepqr slope
Is required to maintain the discharge
through the diminished cross-section,
and the increased slope is obtainable
only by an increased height Of flood
surface above the obstruction. Numer-
Gus actual measurements In the bed
of the river preclude any doubt of the
truth of this proposition. They prove
TINT the escape of water from the chan
mel is accompanied by deposits below,
which fact granted, the other changes
stated followed as consequences of the
elementary laws of hydraulics. The
results have beeh published in detail
and so widely distributed that persons
desiring information can easily obtain
them. aud those otherwise inclined
would not be benefited by their repe-
tition here. One instance, however,
of recent occurrence aud Of momen
tous significance will be given,
During the last flood a crevasse In
the leyee at Nita, La, on the east bank,
about 90 miles above New Orleans,
having o width of 5000 feet and q
dcpth Of Is feet, was found by actual
measurement to have a discharge OF
100000 cubic feet per second, or 80
per cent, of the entire discharge osthe
..-..1:oto,,, ahova Tho rrpvaese.