The weekly pioneer and Democrat. [volume] (Saint Paul, Minn. Territory) 1855-1865, 1859-06-09
The RNek Islaa~ Bridge an Obstruction.
.-TAe O0rsal Doeameas.

report Of the Commissioners, appointed BY
the Secretary Of War, to investigate the
Rock Island Bridge. We give the main
points in the report; there Is enough con.
taiued Il what we publish below, to satisfy
every one The Commissioner, report the
Bridge serious obstruction.
Eurad from the Repovt Of tie United Staies
Com m.ss,ossrs, cent to Eram,ne Ms Ratt-
road Bridge at Rock Island:
lst. The Board is OF the opinion that
the Railroad bridge, which crosses the Ms
sssippi river, between Rock Island and Da-
yepport, Is not constructed according to cor
rect principles, reference being had to the
interests Of navigation.
ID. The piers of the said bridge are not
Of the best form, and there was no practical
difficulty in constructing them OF the proper
form. With the exception OF the turn
table, the Board is Of opinion that the de-
iectiye form Of the piers is matter OF no
material importance. The turn table pier
will be more particularly referred TO in
answer TO the next question.
3d. The only pier larger than is mces-
sary is the turn table pier. This pier, IN
the opinion of the Board, should have been
constructed no longer or broader than was
absolutely necessary to sustain the truss
when the draw is open, and protect it from
injury by passing boats. 1t might have
been constructed with length OF 293 ieet,
afiordipg ample support and protection, and
being actual 1855 feet in lersth. the differ
ence, 80 feet, is unnecessary, aud, in the
Judgment of the board, pernicious. The
effect of making i larger than was abso-
lutely required, is to contract the water
way, increa e the velocity, narrow the draw
passage and present more surface for boats
10 strike against, thus increasing the dlil-
Guilty OF their passages through the draw.
In q pier OF this size the form Of the start.
ing is OF importance, and the upper faces OF
the pier should have been curved surfaces.
4th The piers are not placed parallel
with the current, but at angles varying from
&c degrees to l41s degrees. The effect Of
this obliquity is to treble the obstruction to
the flow Of the water, and consequently to
affect the increase Of velocity in the same
ratio. Another consequence is. that the
passages OF steamboats, and RATS through
the draw and between the piers, are render
ed useless by the formation therein Of All
eddy.
5th. The velocities in the different parts
of the river in the vicinity Of the bridge,
have already been stated, and will be found
tabulated in appendix lCl
9th. The eddy on the Iowa side Of the
turntable pier, as nearly Is could be esti-
mated, is about 100 ieet wide at the foot OF
the pier, and the turbulence 10 the boiling
of the water, extends about 500 feet below.
This eddy, however, is constantly varying
its position and dimensions. It's effect on
the passages of boats ascending and descen-
ding, is undoubtedly to render them more
difficult, on account of the care required to
avoid getting one part of the boat into it,
while another part Is in the current OF the
draw. II has been previously stated that
the effect of this eddy in the Iowa draw is
to render it useless
18th. The surface OF the water at the up
stream end of the turn.table pier, is l6 2
inches above the surface OF the water ut the
down stream end. The extent Of the back
water or remou as nearly as could be est.
mated, is about $50 feet.
9Th. The Bridge is badly located, and il
consequence of this bad location lie greater
obstruction to the passage of steamboats,
than would have been necessary, had the 10
cation been good. Any site in tn, vicinity
below Rock Island, out Of the rapid current
would have been better.
The Board considers it proper to recapit
ulste some Of the well known principles o.
Bridge building. to show how far they have
been coniormed to, or departed from, with
the Rock Island Bridge.
These principles are
LIST. That at given place in locating a
Bridge over any stream, the site where tn
velocity Of the current is a minimum, shou
be selected.
I'd. That in designing bridge, the piers
should have the minimum cross section con-
sistent with the support Of the superstruc,
ture, thus Offering the least obstruction 10
the flow Of the water, ard increasing the
velocity OF the current as little az possible.
Sd. The piers should always be placed
parallel with the thread Of the stream, for
the same reasons as those stated in the second
principle, and because they thu. repder the
passage Of boats and rats less difficult.
4th. In designing bridge over river
having large commerce 10 boats and RATS
the draws and spans should be Of the greatest
practicable width.
In applying these principles to the Rocs
Island Bridge, the Board is coustra inei with
extreme regret to report that all have beer
violated thus rendering the Bridge no
only an obstruction To the navigation Of tht
river, bat one materially greater than tber'
is any occasion for