The daily Gate City. [volume] (Keokuk, Iowa) 1855-1916, 1911-10-02
ton with rock available for founda-

ZION WIN TOck dValldDle LOT lOuuod-
tions only at great depth.
The upper Mississippi, moreover, is
much more regular stream and less
subject to sudden torrential floods
than the two great rivers which con-
tribute large part of the volume OF
the lower Mississippi, the Ohio, COM
ing in from the east, ana the Missouri,
from the west.
The upper Mississippi river derives
most of its waters from Minnesota
and Wisconsin, and the great num-
Der of lakes upon it's watershed con-
duces to regularity of flow. The max
imum variation, according to obser-
vations for over twenty years, is only
l to Is, the minimum flow at Keokuk
being about 10000 Gu. #. per Sec,
and the maximum little over 10000.
1t will be apparent that to take care
of the food waters of stream with
the latter volume is no mean engineer.
ing problem.
The foundation conditions at Keo-
kuk are particularly favorable The
rapids are formed by the flow of the
river over nearly level beds of solid
limestone, and neither the depth nor
the velocity of the flow are sufficient
ly great to offer serious difficulties to
cofferdam construction for laying dry
sections of the river bed. If, however,
1t we're attempted to build dam
across the river according to rdinary
methods, by which the complete struc-
ture is carried across until closure is
finally effected at the center, the
problem of carrying the normal flow
of the river while the last section OF
the dam are being constructed would
be an extremely difficult one, to say
the least
Mr.. Hugh Cooper, the chief engineer
of the project, to whose perseverance
energy and engineering ability the
entire enterprise is due, has adopted
at Keokuk the same method of dam
construction which he successfully
carried out in building the Mccall
Ferry power plant on the Susquehan-
II
was built up with dam sections and
openings alternating. Not until
row of these dam sections was com.
| pleted across the river was the work
of closing the intervals between them
begun. 1t was then matter of com
parative ease to close off from the
water a section between two piers
and lay 1t dry ready for the placing OF
| concrete.
At Keokuk somewhat similar plan
| is being followed, varied, however, to
suit the special conditions. A con-
crete bridge is first being carried
across the river, having piers
6 #. in thickness. spaced 30 tt. apart
surmounted by concrete arches locat'
ed we'll above high water on che COM
4 pleted dam. After this bridge is car
ried across the river, successive sec
/ tions between the piers are closed
off and pumped out and the dam sec
ton is then built up in this 3o-ft
/ space. In building the piers, provision
/ is made for the placing of cofferdam
| protection, with the piers as sup
/ port, when the final closure is under
1 taken.
/ One OF the difficulties in economic
development of power at Keokuk Is
the comparatively small head avail
able. If an ordinary overall dam
were carried across the river, It's
crest would have to be placed at such
low elevation, in order not to give
too great height to floods back o.
| the dam, that only low head wouic
be available during the low-watei