The Cairo bulletin., 1910-01-30

ing walls or by revetments.
lation of the entire bed OF the stream
by ilyation in sufficient number i'm,
on predetermined slope, Of the crest,
OF controlling bars. whether thes,
bars be natural or Artificial, thereby
eQuali2ng the fall and preserving ;
Uniform recurrence of neither nor,
nor less tEan the required depth an,
width OF cross section at these deter
mining points for complete regulat on
to be accomplished by aiudams OF
crossweirs, THIS maintaining the de
sired depth CT channel when ohtaine
| BY the works Of s:dc;contraction an
IEankprotection.
Hydraulic dredging is proposed as
an auxiliary process to assist the nat
irral forces and hasten the develop
ment of the proposed channe. Not
Only during construction. but after
the completion Of lie permanent
works small amount OF dredging viii
| be necessary 20 hasten ne removal
OF temporary s'o&-s caused by fall
IN stage so rapid that even ccm.
pletely improved ~'.-5r Will be unable
to correct Itself simultaneously with
decrease in stage.
Briefly stated, this project for open
river Improvement by a regulated
channel with sil:,;1ms or cross-weirs
Is intended to eouaii2e AMI render
more uniform the water-prism at all
points throughout the length to be
improved. and at all st ages beow
the bank-full stage; to reorgani2e. hut
not radically to alter the bed OF the
stream. Transforming the bad passages
into good passages by substituting for
the natural controlling bar or uniform
artificial bars or we irs, when shall
maintain fairly uniform slope and
constant gauge hets..t Ter a given
volume of discharge, aid to smoota
out the present great Irregularities of
the stream, both as to the varying
width and depth now obtaining in
such way as to produce and maintain
at low water. a practicable channel
with a nayigabe depth OF fourteen
feet. The places where too great
width and insufficient depth now
exist will be replaced 0y a regulated
channel of the proper width to pro
duce the requisite depth at the pres
ent available low-waIer discharge and
without material change in the e,eva-
ton OF any stage.
The gorge between Grays Point ami
Commerce eXempiifies the effect Of
natural conditions similar to those
that should be produced by artificial
control for seven miles the river is
confined between stable banks, the
low.water. and the bank-fulI widths |
compare favorably with CORES ponding
mean widths for the district. ami the |
slope is not only slightly less than |
the mean slope; at certain places ire
bottom is fixed or practically so. re.
slit'ng in mountaineering cross-sec |
ton. and except for Isolated bOulders |
and reefs, the required width and |
depth are found, Permanent nayi. |
gable depths not only exist through |
out that reach. but extend for three
to four miles above S1d below.
1t IS proposed 90 create an essen.
tally parallel condition by means of
works for complete regulation in parts
OF the river where the cross.sectiun
varies from the one required TO main.
tain a navigable depth Of fourteen
feet.
For such localities. the required
section having been determined
the boundary lines of the stream will
he conformed to that section by the
building or erosion OF the banks to
the desired alignment BY side-con.
traction works. the protection when
necessary, of all unstable banks,
whether naturally or artificiaHy pro
duced, and the determining in eleva
ton OF the Bottom at the necessary
intervals, by silIdams or cross weirs
To obtain this result, the weirs will
De placed across the alluyial bed Of
the stream and approximately norma
10 the chosen thread of channel.
SllI-dams or submerged cross-weirs
as means of controlling the stream
depth have been III use many years.
on European Rivers. In
Germany they are called "grund-
schwellen.' In many cases they have
been resorted to for the purpose Of
raising the low-water plane after con.
traction works alone mad resulted in
too much securing of the bottom.
they have not yet been used in 50
extensive plan, nor on so large
scale as in this project