The sun. [volume] (New York [N.Y.]) 1833-1916, 1897-05-23

quantity of water would DO thrown into the
the quantity OF material would be Increased
fourfold, and even this would not give porma-
nent security unless there could DO positive evil
dence that there would be no deposits TO cause
an elevation in the bed OF the stream.
OF enormous magnitude, is proved by tho fact
that tho bed. of the stream In the upper part OF
its course has, been raised by such deposits,
even without the aid of artificial levecs, TO n
height of over 800 feet, and that, too. by the com.
parativcly small percentage dropped. in tho
stream itself. the greater portion ~ the trans
ported material being scattered over an area OF
hundreds Of square miles.
Since only the finest particles OF mud arc car
ried into the Cult, all the heavy material, as
also all the wash from the banks, must nccos-
S wi,h h GS Sac cp0tinnn rn ' IsyG SeS 81 th SrC S y na ot her
place where such material could be deposited,
and 1t is not within the bounds Of possibility
that levccs could be constructed so high that
the floods in time would not ovcrtop them. Tho
statement that recently constructed levecs have
sisted is. no doubt true. but why 1t is because
other places have been weak and have given
way. Crevasses have occurred and relief has
thus been afforded. and there are still numerous
outlets, as safety. valves, that have not yet been
closed. Close all tho outlets and make the
levecs continuous, and the history OF the Hoang
Ho will be repeated in the valley of tho lower
In a Valuable paper by Prof. ]. u. johnson,
read before the American Association for tho
Advancement of Science, September, 1884, this
1T would seem, therefore. that in the rivers
present condition there is no evidence that a
u CoUlllltu huOu VIII SNOuT u lS = ~ w W
facilitate the discharge. and there is consider
able evidence against Il; II the river flowed be-
Eads has constructed at tho mouth of the river.
then there could be no such thing as discon-
no alternate scour and ali. Then Concentration
OF volume would be beneficial and would ulti-
mately lower the river bed. But this condition
River, and hence the concentration of food vol
ume will be harmful rather than beneficial"
The conclusion from n voluminous array OF
facts, opinions, and testimony is simply this,
that leyees are necessary locally to prevent over.
with closed outlets will increase the height OF
floods and render them moro unmauaseable.
THE OUTLET SYSTEM.
The advocates OF the outlet system claim the
ability to reduce the height of the floods and pre-
moro rapid discharge OF the water in time of
flood by u more direct channel to the Gulf
1t Is stated that a crcvnsse at Bonnet Care, a
short distance above New Orleans. which dis
charged one.twelfth Of the flood water through
Lake Pontchartrnin, in going six miles instead
Of l60 miles TO the rivers mouth; lowered the
four feet, where the rise and fall was seventeen
feet, ind lowered il at Natchez. 800 miles above,
FROM six to eight feet. where the rise and fall was
Ii is also claimed that an ntlct one mile wide
by ten to twelve fee, deep. with a fall of twelve
feet in going six miles to Lake Borgnc, would
divert Oue-twelfth more OF the discharge and re
duce the h~igh-water level at New Orleans in all
to fifteen feet.
There can be no question that outlets will great
! ~ TeuuCc inc ItlEn Ol lloDls u pTOptTlN lONhltA
and OF sufficient number and size. In fact,
nature provides them for, its own relief. by
to localities many miles distant. 1t would seem,
therefore. that permanent outlets properly To-
is made that the change in the velocity of the
currcnS below the crevasscs causes the fortna-
ton of bars and results in an impeachment to
This objection would have less force at the
proposed Lake Borgnc outlet. az the bottom OF
the stream is below the surface water OF the
Gulf. and the current is too feeble to produce
much OF a scour at any time. The diversion of
one.twelfth OF the flood waters would reduce
1t would not be difficult: by means of an outlet
of sufficient size to turn tho bulk OF the waters
of the Mississippi into the Atchafalaya. which
would give n shorter distance to the Gulf. a
sleeper slope, and q more rapid disGhaTge, leav'
What is needed is TO maintain in the Missis-
sippi the depth for navigation, and discharge the
excess as rapidly and By as many outlets as
possible. which requires that the outlets should
not permit IA discharge at too low a level.
CONTRACTION.
Contraction Is n local remedy to produce a
scour for the removal OF bars and deepening Of
navigation. 1t consists in reducing the cross
section and thereby increasing the velocity at
certain points. In some cases ii may be eNpe-
dent to resort TO dredging. TO secure u channel
that can afterward be readily maintained in low
water by n contraction OF the cross section. 1t is
in general easier to maintain a channel than to
create it by means OF scour. Contraction is one
Of the auxiliary means to which the engineers
must resort in special cases. 1t is not applicable
10 continuous Improvement.
REvETMESTs.
A river flowing through an alluvial plain has
n constant tendency to change its course and
produce a series OF horseshoe curves. The con-
slant erosion gradually reduces the distance
across nj the heel OF the shoe, and at length u
high flood breaks over and cuts away the inter
vcning neck OF land and creates a new channel.
leaving in place OF the old channel IL bayou often
many miles in extent.
This action often lnenaces important cities
such AS Nicksburg and Memphis and renders
necessary protection against the croding action
o. the stream.
interest OF navigation that the bank OF the
stream should be protected from this erosive
action, since the vast amount OF material re-
moved must be redepositcd at other points in the
bed OF the stream, forming serious obstruction TO
navigation.
The protection OF the banks by revetments is
therefore an object OF primary Importance. and
the benefit to be derived thercfrom is not merely
question of navigation rather than the protec-
ton OF plantations from overflow.
THE TRUE SOLUTION OF THE PROBLEM.
The objects sought are twofold-to maintain
a navigable channel and to prevent the dcstruc.
ton OF life and property by Hoods,
The evidence presented should be conclusive
that parallel lcvees of any height, continuous on
both sides OF the stream with outlets closed. will
not secure the, country permanently against
protection shall have been attained the damage
from breaks will be vastly increased.
On the other hand, outlets at low water level
may divert SO large "A volume as to reduce the
amount below the limit required to maintain
What, then. is the remedy Evidently to Sc.
cure n rapid discharge of the surplus waters of
floods and retain the volume required for pur-
poses of navigation.
Fortunately the means securing these results
are so simple and SO entirely In accordance with
the practice OF hydraulic engineers in similar
cases that it is really surprising that tho prob
lem should appear TO present any difficulty, and
that suggestions should have been made of n
liberal premium to tho engineers of the world
for plans that will secure the desired results.
The remedy is found In the construction, not
o. outlets. but of waste weirs.
THE WASTE WEIR SYSTEM,
Every canal engineer understands that in
constructing n summit level to supply lockage
for his canal he must provide waste wcirs, so
that when foods HI the feeders and the canal
level. to n certain height the surplus will be di.-
charged over weirs into the natural wafer
channels of the country. and thus prevent a rise
} that would endangcr the banks.
BY "A precisely similar arrangement extensive
wcirs could be provided al suitable points along
the Mississippi, OF which there arc many. which
would be inopcratiNc under ordinary nayigablo
conditions of the stream. but when the rise
reached "A level. TO 0c determined by the en-
ginccrs in charge, tho surplus would begin to