Evening star. [volume] (Washington, D.C.) 1854-1972, 1913-08-01
THE KEOKUK DAM.
1.-The Engineering Feat.
By Frederic J. Haskin.

The big central fact about the greatest
water power plant in the world is the
| dam itself, the colossal barrier of con-
crete that halts the Mississippi on its
| course to the gulf and diverts it's waters
| through a power house where their
energy may be used to make electric
] power.
/, No such dam ever was built before, no
| such river ever was halted before. there
were no presidents and no guides to fol-
low. 1t was an engineering problem as
| difficult in it's way as that at Panama,
and one the solution of which can stand
only second to that of the great canal.
| Here at Keokuk is the foot of the Des
Moines rapids. place where nature had
| already done much to help the work. A
glacier once damned the wider course of
| the river to the west and then this chan
mel was cut through in valley much
narrower so that the bluffs on both sides
Of the river are quite close together. In
the twelve miles above Keokuk the water
| falls twenty three feet, and it is these
rapids that have always obstructed navi-
| cation in the upper Mississippi. To dam
these rapids practically mile wide from
shore to shore, and to dam them in
climate varying from 100 degrees above
1
| under conditions where a winter bonn
| bardment of ice was to be expected and
! to be feared but little more than spring
| deluge, admittedly was a difficult under
| taking.
/ The power house was to be on the Iowa
| side The dam was started from the
| Illinois side. keyed into the limestone
| bluff and built out into the river under
| the protection of an advance cofferdam.
| Another cofferdam unwatered the bed of
| the river on the poWerhouse site. Includ-
| ing the abutments the dam is a mile
| long, but the dam itself, the 119 concrete
spans, measures 4,2Is feet or over four
| fifths of a mile. Each pier is six feet
| thick. the distance between the pier-the
inside measurement of the spans-is thr-
ty feet The viaduct that tops the dam
structure is twenty-nine feet wide and
| the dam at the bottom of the river is
forty-two feet wide.
When these piers were finished the dam
had the appearance of many-spanned
bridge, for there
Little Resistance was nothing be-
to Flow of River. and tna ,H' off p,e,
comparatively little obstruction to the
river flow The spillways between the
piers were built i'm later. On the upper
side they have a vertical face, but on
the downstream side they are so curved
down and out that their surface is Just
the shape of the under side of the water
as 1t falls over the top of the spilIway
These spillways were built gradually so
as to offer the minimum resistance to
the flow of the river. The work was
done by building slowly from one side
or the river to the other, and also by
building slowly from the bottom up. Five
feet OF concrete was laid at first between
two piers. the only obstruction then be-
Ing one thirty-foot cofferdam in the
whole stream. Span at a time was
| filed in in this way until the bottom
layer was finished. Then another five
foot layer was built all across, span at a
| time, and SO on until the last layer
brought the top of the spillway sections
| to thirty-two feet above the river bed.
On the up-river side of each span slots
were let into the sides and into the top
of the spillway, in which slots slide 10
steel gates. These can be let down SO
as to form complete obstruction to the
river. These gates are eleven by thirty
two feet in dimensions, and will be
raised and lowered by ELECTRIC power,
each being operated singly from an cleo
| trio travelling crane on top of the viaduct
| the dam at constant level, never vary
| ing. In high water they will all be
| open and the surplus will flow through.
| In low water a sufficient number of them
will be closed to maintain the desired
| level
| Concrete is mixture of sand, crushed
| rock, cement and water. This is the
| biggest concrete structure in the world,
| and therefore the nature of this part of
| the work was of great Importance A
| bed of ideal sand was found on the Illi-
nois side only two miles below the dam.
| and no less than 100000 cubic yards of
| 1t were used. Loaded on wagons all at
| one time this would mean a procession
| of sand carts that would reach from
New York through Denver to the west
ern boundary of Colorado. Stone for the
crushers was taken from the bluffs at
| both ends of the dam, largely stone that
| had to be excavated anyhow. The
| ment came up the river from Hannibal,
sixty miles below.