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*High water of 1844 was extraordinary on the Missouri, some 15 feet above ordinary floods at Kansas City and about 6 feet above at Saint Charles.

CHAPTER IV.

DESCRIPTION OF BRIDGES ON THE MISSISSIPPI RIVER FROM SAINT PAUL, MINN., TO SAINT LOUIS, MO.

Introductory remarks-Outline of treatment of each bridge-SAINT PAUL RAILWAY DRAW-BRIDGE-SAINT PAUL ELEVATED HIGHWAY BRIDGE-HASTINGS RAILWAY DRAW-BRIDGE-WINONA RAILWAY DRAW-BRIDGE-LA CROSSE RAILWAY DRAWBRIDGE-PRAIRIE DU CHIEN PONTON RAILWAY DRAW-BRIDGE-DUBUQUE RAILWAY DRAW-BRIDGE-CLINTON RAILWAY DRAW-BRIDGE-ROCK ISLAND RAILWAY AND HIGHWAY DRAW-BRIDGE-BURLINGTON RAILWAY DRAW-BRIDGE-KEOKUK RAILWAY AND HIGHWAY DRAW-BRIDGE-QUINCY RAILWAY DRAW-BRIDGE-HANNIBAL RAILAND HIGHWAY BRIDGE-LOUISIANA RAILWAY DRAW-BRIDGE-SAINT LOUIS ELEVATED RAILWAY AND HIGHWAY BRIDGES-BRIDGES ON THE MISSISSIPPI BETWEEN SAINT PAUL AND SAINT LOUIS AUTHORIZED BUT NOT BUILT.

WAY

Introductory remarks.-When this report was ordered by Congress in 1866 there were but two of these bridges, as they now stand, in existencethe elevated highway bridge at Saint Paul, and the low railway drawbridge at Clinton. The former bridge has practically never been any obstruction to navigation. The Clinton draw-bridge was without authorization by Congress, but was declared a post-route in February, 1867. It is the bridge with the narrowest draw-openings authorized by Congress, and has but one draw-opening available. The old draw-bridge at Rock Island was then standing, but Congress had never authorized it, and in 1866 initiated legislation for its removal, which finally took place in 1872.

This bridge was undoubtedly the worst artificial obstruction to navi gation that has been built on the Mississippi. With the exception of a very complete report upon the old Rock Island draw-bridge by the offi cers of Topographical Engineers, Humphreys, Meade, and Franklin, made n 1859, there was no published official report of any of the bridges on

the Mississippi, or of the best kind of bridge within practicable limits to avoid obstructing its navigation. This chapter, therefore, supplies a want in the consideration of the main question of great value. The number of draw-bridges now built, and the variety of circumstances under which they were constructed, seem to be sufficient to apply the test of experience and exact observed conditions. The observations made run over periods of low and medium high-water stages at many places, and are of a kind that requires time in order to obtain opportunity to observe them. I have concluded the report upon each bridge with remarks upon its effects on navigation, and with opinions from the report of the board of engineers upon sheer-booms, of which Colonel Macomb was president, I being a member, and to which the maps accompanying this chapter were submitted, recommending certain modifications for the benefit of rafts. I have also made suggestions for changes to facilitate the passage of steamboats; but, to quote the language of the board just referred to:

The plans and locations of most of the bridges are such as to make any complete measures for the safety of navigation impossible. (Annual Report Chief of Engineers for 1877, p. 827.)

Outline of the treatment of each bridge. This order is followed as closely in all cases as the differences which are presented will admit. It is necessarily departed from somewhat in giving an account of the Rock Island bridge, which was designed by me.

NAME OF BRIDGE.

When built and opened.

Authority. To whom granted.

DESCRIPTION OF RIVER AND VALLEY AT THE LOCALITY.

Widths at low and high water; terraces; bluffs; rise from low to high water; slopes; bed of sand or rock; peculiarities.

SURVEYS MADE.

When; to what extent; for what purpose.

DESCRIPTION OF BRIDGE.

Approaches and arrangement of spans; grades.

Substructure; foundations; dimensions of piers; pivot pier and guard. Superstructure; kind of; by whom built; management of draw; management of bridge; accessory works.

INFLUENCE UPON NAVIGATION.

Upon steamboats; upon rafts; directions of current; velocity; accidents.

ALTERATIONS TO LESSEN OBSTRUCTIONS.

To rafts; to steamboats.

HIGH BRIDGE.

Approaches; height above low water.

SAINT PAUL RAILWAY DRAW-BRIDGE.

(Opened for travel in 1869.)

The only authority for building this bridge is in the act of the legis lature of the Territory of Minnesota, approved February 20, 1855, incorporating the Southern Minnesota and Root River Valley Railroad Company. Section 11 of that act contains the following:

For the purpose of constructing and using said railroad the said corporation is authorized to construct their said railroad and the necessary bridges across and over public highways and navigable streams: Provided, That it be so done as not to obstruct or impede the navigation of any navigable stream.

* * *

By act of the legislature of Minnesota, approved May 22, 1857, the above-named company was authorized to build a railroad from Saint Paul and from Saint Anthony to a junction at Shakopee, thence up Minnesota River, with the same powers, &c., granted to the company in act of corporation. By act of legislature of Minnesota, approved March 4, 1864, the above-named corporation was divided into two corporations, "The Southern Minnesota Railroad Company," and "The Minnesota Valley Railroad Company." By act of legislature approved March 1, 1870, the latter name was changed to Saint Paul and Sioux City Railroad Company. This company built the bridge and operate it. The Milwaukee and Saint Paul Railway Company run their trains over it.

DESCRIPTION OF THE RIVER AND VALLEY AT THE LOCALITY.

(See Diagram 4.)

The width of the low water river at the site of the bridge is about 1,300 feet; within 1,000 feet above this width decreases to 700 feet. The high water width here is about 3,000 feet. The left bank is bounded by a low rock terrace about 50 feet high; on the right side of the valley the bluff rises to the height of 125 to 150 feet. This bridge is but 2 miles above the highway bridge at Saint Paul. The rise from low to high water is about 22 feet. The current is gentle at low water; at high water it is probably as much as 6 or 7 miles per hour. The slope of the water's surface is about 1 foot per mile.

The bed of the low water river is composed of sand; its depth is not known to me.

SURVEYS.

In September, 1866, a survey was made of this section from mouth of Minnesota River, 4 miles above to 9 miles below. This survey de termined the lines of the low banks, of the overflowed bottom lands, and of the bluffs, the slope of the water's surface, and, by soundings, the depth of the river. The survey was made with a view to obtain a knowledge of the river preparatory to devising a plan for its improvement. The piers of the bridge had been commenced at that time and careful soundings were made about them. In October, 1868, a special survey was made at this bridge, including soundings and current observations. In September, 1876, an examination was made, but no current observations were taken, they having been made by Colonel Farquhar, in July preceding.

DESCRIPTION OF BRIDGE.

(See Diagram 5.)

Approaches.-Commencing at the bluff on the right side of the valley the bridge approach crosses a lagoon or lake called Pickerel Lake on a

curve of about 1,340 feet radius, and about 1,100 feet long, then on a straight line to the abutment on the left bank. The left bank approach is on a curve of about 1,145 feet radius. The approach on the right bank is of trestling resting upon piles sawed off near the surface of the ground and in the lake just above low water. The approach on the left bank is on an embankment.

Arrangement of spans.-The first span, commencing on the right bank, is 150 feet from centers; the next two (pivot-draw), 270 feet from end to end, with clear openings of 114 feet; then six spans, 150 feet each; in all 1,320 feet from end to end of bridge.

Substructure-The piers of this bridge are, with the exception of the pivot, 22 feet long, and 7 feet wide on top, with a batter of inch to the foot. All have triangular ends, except the one standing on the left bank. The pier to the right of the pivot, the pivot, and two piers to the left, rest upon piles cut off below low water. The others rest upon the bed of the river, and are protected by riprap. The pivot-pier is circular in plan, 30 feet in diameter. All of the piers are of masonry. The stone for them came from the bluffs in the immediate neighborhood, and is magnesian limestone. All of the small piers standing in the river, except the one on the right of the pivot, have detached ice breakers. These ice-breakers are timber cribs filled with riprap, resting upon the river bottom; they are rectangular, with a triangular nose or starling, with a slope of 2 on 3; dimensions on top 12 feet wide, 19 feet long, with the nose 9 feet, making whole length 28 feet on top. All of these icebreakers, except the one to the pier on the left of the pivot, are placed on a line, making an angle to the left of 15 degrees with the axis of the piers. The pivot-guards or draw-rests are timber cribs, planked and weighted with riprap.

Superstructure.-The bridge is a wooden Howe truss; the short spans are 22 feet high and 19 feet wide out to out. The draw-span is 9 feet high at the ends and 26 feet at the center. The bridge truss was built by the Saint Paul and Sioux City Railroad Company. The draw is opened and closed by men with levers.

At the time of our examination, in September, 1876, the company were putting bents of trestle under each span, the bridge baving become unsafe by the decay of the chords. This early decay (the bridge had been built but 6 years) of the timber in the chords is said to be due to want of care in its selection, and to the use of oak wedges in the pine chords. The acid of the sap from the oak wedges is said to have caused decay in the pine. An examination of the chords where most decayed showed it had taken place to a greater extent about these wedges than in other parts, but whether more than is properly chargeable to the excess of moisture here, I cannot say.

The whole bridge superstructure, except the draw-span, was to be rebuilt in the winter of 1876–77.

INFLUENCE UPON NAVIGATION.

In 1866, 1867, and 1868, the channel of the river was along the left bank at the foot of the rocky bluff from Williams's Ferry, 5,000 feet above the bridge, to a point 1,400 feet above the bridge; from this latter point the channel crossed to the right bank, reaching it a short distance below the bridge. This crossing was gradual through this distance, so that the piers of the bridge were nearly parallel with the current. This was the case when our current observations were made in 1868. At that time the piers were partially built, all of the foundations being

in, and the masonry built to the level of the water. The pivot-guards and ice-breakers were not then built. Current observations made in July, 1876, by Colonel Farquhar, United States Engineers, with the water at 3.1 feet above low water, show a marked change in the direction of the current. The "crossing" from left to right bank, instead of commencing at a point 1,400 feet above the bridge, commenced only 600 or 700 feet above, the current crossing the bridge axis obliquely, making an angle of 10 degrees with the axes of the pivot guard and rest-piers. This change in the direction of the current was due to the formation of a bar running out from the right bank above the bridge; the lower end of this bar, at the time of these observations, was within 500 feet of the bridge. This change has made the right draw opening unsafe, and it is never used by steamers descending the river.

ALTERATIONS TO LESSEN OBSTRUCTION TO NAVIGATION.

It is probable that the extension or recurrence of the sand-bar cannot be prevented without rectification of the river for some distance above the bridge. This the bridge company should be compelled to do for the sake of the navigation on the Minnesota River.

HIGH BRIDGE.

High ground could have been found for the approach on the let bank where the width of the valley would have been but 3,300 feet. This length of approach is small in a high bridge over so large a stream as the Mississippi at this point. A continuous bridge here should not be less than 77 feet above low water.

SAINT PAUL HIGHWAY BRIDGE.

(This bridge was commenced in 1857, and completed and opened for travel in 1858.)

Authority. The building of this bridge was authorized by the Terri torial legislature of Minnesota, by act approved March 4, 1854. This act is entitled "An act to incorporate the Saint Paul Bridge Company." Section 12 of this act, which contains the provision fixing length and height of spans, and provisions in reference to navigation, is as follows:

Said bridge shall be of such material as the stockholders may deem expedient, and shall be so constructed as to cover the main navigable channel of the river by a span at least three hundred feet from pier to pier, the lowest part of which said span shall be at least sixty feet above high-water mark, and said company may construct other abutments, piers, and guards to said bridge, at such distances from each other and at such places as may be deemed necessary, either on the street from which such bridge shall lead, on the island opposite said street in the said river, or on the mainland on the opposite side of said river: Provided, That nothing in this section shall be so construed as to warrant the obstruction of any public street or the navigable channel of said river.

The span over the main channel was built 240 feet long instead of 300 feet, as provided by the act. I have not been able to find that any ad ditional legislation changed the provisions of the act here referred to.

DESCRIPTION OF THE RIVER AND VALLEY AT THE LOCALITY.

(See Diagram 4.)

The Mississippi River, at the site of the bridge, is divided into two chaunels by an island. The distance between the low-water banks on

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