The daily Cairo bulletin. (Cairo, Ill.) 1878-1???, 1882-11-29

|
with view Of protecting the lands from
inundation. The plan Of the Mississippi
river commission, while it recognizes the
importance Of
MAINTAINING THE LEyEEs
Of the Mississippi in tact during the pro-
gress of the improvement, look to the ulti.
mate disuse Of the levees altogether. All
| sediment-bearing rivers have naturally
| high water channels differing very greatly
in width. At some places In the Missis-
sppi the high water channel IS several
miles wide while the normal width ia only
about 5000 feet These wide places are the
disturbing elements which create caving
banks, shoals and shifting channels. The
dikes Of leyees inclose these wide places
and consequently do not tend TO produce
a uniformity Of current The plan of i'm
provement recommended by the commits
sion differs from any other previously pro-
posed in The fact that it looks to a rectif-
cation of the high water channel by the
ultimate narrowing Of these wide places as
the only method by which deep and uni.
form low-waer channel can be permanent
ly secured. J.
There are three great principles govern
ing the problem They arc very simple
but unless they are fully comprehenied it
is impossible for any enc to form correct
judgment on the subject The first is the
force producing the current: the second is
the friction OF the bed which is the force
rctarding the current, and the third is the
intimate relation between the quantity Of
sediment suspended in the water and the
velocity OF the current. The first force re.
suits from the surface slope of the river, or
the fall Of the water from higher to q
lower level. The friction Increases as we
increase the surface Of the bed in contact
with the water. Hence, at the wide places,
the friction is greatest, This causes loss
of current; the sediment cannot be held up
in the water and it is consequently de-
posted in these places, aud this produces
sleeper slope Of surface and make an in.
creased height Of levee necessary. If the
wide places are narrowed, friction is re-
duced, and an abnormal current will then
result, owing to the steep slope of the river
at such places. This current rapidly cuts
away the bottom in the restricated width
and dcepens it; and as each one of the wide
places becomes thus deepened
THE sTEEPNEss OF SLOPE
OF the surface Of the river Is diminished or
lowered, and hence makes such high levees
unnecessary. The gain by the reduction of
the surface slope simply through this mar
rowing of the wide places between Red
river and Cairo, distance of about 800
miles, amounts to sixteen or eighteen feet
at Caro- The importance of the levees as
means of improving the navigation of the
river comes wholly from the relation which
the volume Of a sedmontary steam bears to
the fractional resistance Of the bed. If the
volume be diminished the ratio of friction
to the volume will be increased. Conversely,
if the volume be increased, the ratio of re-
slstance will be decreased; higher veoci.
ty OF current must result and greater
amount Of sediment will be transported. If
this amount be greater than that which
the tributaries bring INTO the river the
difference must be taken up out of the
bed to the benefit Of navigation, and the
flood line must consequently be lowered.
A uniform width OF the high-water channel
must produce uniform depth and uni
form current. Cavlng banks cannot exist
where the current is uniform through any
considerable length Of the river, because
tho water will then be charged with sedi-
ment to its fullest capacity and it cannot at