The Greenville times. [volume] (Greenville, Miss.) 1868-1917, 1877-12-01

49, 49, 49, - - -
ID along the bottom Of the river.
:. That IL quantity npAeld de.
pends upen The velocity Of the
current, modified By the depth II
the water. 5. That the quantity
Of sediment annpally discharged
into the sea and over the banks Of
the river throughout its alluvisl
basin muat be. during any long Pc
riod Of years, about equal to the
amount poured into::'he trunk by
it's tributaries during that period
II 1t discharged less than II receiv-
cd the bed would Gil up; 1t It dis.
charged more the difference would
have to be taken from Its bed ;
whereas there il no proof Of any
sensible alteration in the site OF its
channel during many years. Tho
current must therefore be 80 regu-
lated BY the river that II will dis
charge no more nor no less than
tho amount received.
From these facts Captain Eads
declares that alterations from the
normal velocity Of current produce
deposit aud scour, tho normal We
!ocity being assumed No that rate
which will uphold and carry for.
ward the sediment without loss Or
increase OF quantity. BY the ac-
ton of deposi, and scour the river
10 able tv restore the normal ve-
locity when from any cause II has
been disturbed The alluvial basin
beius composed wholly Of matters
deposited BY tho curreut, It can
again remove them from tho cham
mel by scour II tho current be too
rapid, or add 10 them by deposit
II too slow.
The friction Of tho water in con-
tact with the river bed, Is the chief
retardipg the current. Tho
inclination, or slope Of the suriace
Of the stream determines the in
tensity Of the force OF gravity,
which produces the current /; thus,
u the friction DO greater ut one
place than ut another, and an equal
bc required ut each, the
slope must bs sleeper where the
friction is greater than where II is
less. The normal current being
absolutely necessary TO maintain
Inc capncity Of the channel unal-
Icrcd und the friction being much
greater vt sumo localities than
others. we must expect 10 SEE great
iiycrsit, II, the slope Or inclination
Di the foud line Oi tho river. These
liversities do exist. The lowest
slope exists in the 100 miles between
The passes and New Orleans, where
II is less than AZ inch and half
per mile; while the steepcst slope
exists IN the river from Cairo to
Memphis, wncrc II averages nearly
Eve inches, and the bayou Atcha-
falaya, where II Is about six inches.
As the channel OF the river is con-
'inually shifting, especially IRON
Cairo TO Red river, bends caving
n, and cut-ods forming, IL follows
hat tho river must possess some
means Of establishing and altering
!hcsc slopes to regulate the cur.
tent, 50 that through all these chan.
scs II shall maintain the capacity
'r size of the channel intact, and
10t run riot. This Is done By
'c0ur Ind deposit. Too much vc.
ocity incroascs the suspending
power VI tho water. and it tukcs
ip the material Of which tho bed
. formed. This Is called scour,
md tho result is a deepening Of the
'hannel aud y lowering of the SUR
ace slope. Az this IL lowered the
'urrent falls to the normal rate
Ind the scour ceases. II the cur
'ent be too slack the water cannot
lpaold Its burden, portion falls
Ind builds up the bottom. This il
allied deposit. As the bottom ri.
'es the food slope increases, and |
hc current becomes more rapid, |
mil finally II flows 50 fast that
he normal speed Is established |
md deposit ceases. Raising the
lopc necessitates raising the lsvees
lust % the slope can bo lowered
AN lcvecs be dispensed with.
Whatever increases resistance to
he how Of the water makes steep.
y slopes and higher levees ineyi-
able. Friction Of the bed Of the
treanl does this to . much greater
xtent than all the other rctarding |
nnuences combined. This Il least
vhers the strsam b Marrowesf, |
nd II 10 lessened II ratio a. the
'olulne Il increased. For instance, |
rom Red river 10 the Passes, $40 |
niles, The slope Il about one and
hros quarter incl,es per mile. Ii
he river were divided lutO two
quail strsains. ih's slope wOuld be
much sleepsr IN carh and thu lss. (
Is would have 10 IN hIxaer.
"a. pu .lscha.Ias u, At He'd river.
akes ofi abDut unc-,enth Vi tile
olunls ~ 'he sea, with . slope of