The sole objection to this location lay in the southern approach, which made it necessary to leave the bridge on a sharp curve, and involved a cut 70 feet deep; these were matters of little weight when compared with the merits just enumerated.*

Great care was taken to ascertain the exact direction of the current and the bridge line. Observations were made with two transits simultaneously on a number of floats; the result of these observations was mapped out on a chart, and the direction of the current was thus accurately determined. The course in mid-channel as thus obtained made an angle of 72° with the bridge line; the piers were located parallel to the current, and the bridge built on a skew of 18°. The floats used were made by inserting a rod, to which a small flag was attached, in the neck of a bottle loaded with shot, the amount of shot being sufficient to sink the flag nearly to the surface of the water. These floats drew, on an average, about four feet, or the usual draught of a Missouri River steamboat; they therefore gave the true navigable current. The direction of the current varies a little with the stage of the water, as well as with the different forms which the smaller sand bars assume in successive years, but during the season of navigation it has not been found to show any material divergence from the line thus determined and given to the piers.

The pivot pier was placed in the centre of the channel; the piers were numbered from the southern end of the bridge, and the lengths of the several spans were as follows: a fixed span of 132 feet, extending from the shore to Pier No. 1; a pivot draw 363 feet long, each arm having a clear span of over 160 feet, as required by the Act of Congress; a fixed span of 250 feet from Pier No. 3. to Pier No. 4; leaving a remaining distance of 577 feet divided in the original plans into three spans of equal length, though subsequently changed to two spans of 200 feet each and one of 177 feet; to this must be added a shore span of 68 feet at the south end, extending over the width of a street and the Pacific Railroad track, and which made the total length of bridge from outside to outside of masonry 1,400 feet. The lengths of spans given here are gross distances taken from centre to centre of the adjoining piers. The nearness of the channel to the south bank made it impossible to place a span of 250 feet

*The profile and alignement are given on Plate II.

on each side of the draw, as required by the Act of Congress, without neglecting the more important provisions of that Act, which requires the draw to be placed over the centre of the navigable channel. The requirement of two spans of that length was made, as has already been stated, with special reference to the Mississippi, where raft navigation forms an important part of the river commerce; on the Missouri, raft navigation, except on the most diminutive scale, is impossible, owing to the sharp curves, strong current, and multitude of snags, while no sufficient supply of good timber is found along the river to make rafting profitable, even if it were possible. Endeavoring to conform as nearly as possible to the Act, a span of 250 feet was placed immediately north of the draw, but the unexpected destruction of the foundation works of Pier No. 4, in the spring of 1868, made a further change necessary; the site of the pier was moved 50 feet farther south, and the long span finally built between Piers 4 and 5.

The month of April, 1867, was distinguished by a very extraordinary spring flood, caused by the united freshets of the Platte and Kaw; on the 29th of the month the river had risen to 119.3, three feet and three inches higher than the June flood of that year, and four feet above the highest water of either of the two succeeding years. During the war the Government had established a supply station in the bottom west of the town, and a small portion of the bank had been protected by a covering of riprap, to serve as a steamboat landing. The river had washed the bank away both above and below this protection, leaving a projecting point, the end of which alone was covered with stone; though the whole discharge of the river passed outside of this point, strong eddies were formed on each side of the neck of land connecting it with the shore, which gradually reduced it to a long and narrow isthmus. On the 10th of April the width had been reduced in places to only 18 inches; on the following day the two eddies met, entirely destroying the neck of land, and allowing the channel of the river to shift at once from the north to the south side of the rocky point, changing its position nearly 500 feet in a single day. The pile of rocks still remains in its old place, having been left almost dry on the north side of the river during the low water of December, 1867. As the channel shifted suddenly from the north to the south side of it, it has never been

exposed to the most violent force of the current, but its height has gradually diminished, and it will in time sink out of sight.

The stone protection above the bridge was begun during this flood, and continued through the summer and early autumn of the same year; it was carried westward from the point where the rocky bluff and shore line separate above the bridge, to within 150 yards of the State line. This protection was executed under the direction of the engineers, a portion of the expense being borne by the city. It consists of a simple revetement of riprap stone, a large portion of the stone used having been taken from a cut in the southern approach to the bridge. Whenever practicable, the shore was first worked by laborers to a slope of about one to one, and the stone was evenly distributed over this slope; but when the revetement was begun, the water was too high to admit of this, and the stone was simply dumped over the bank, till the heap appeared above the surface of the water. This protection has required some repairing, the stones having slid down the slope, replacing the soil which the river had washed from beneath them; but it has proved perfectly effective, and the river has in no instance changed the line of the protected shore. In the following spring the protection was extended to the State line, and during the low-water season of 1868-69, it was carried, in the interest of the land owners, as far as the mouth of the Kaw.

The railroad approaches the bridge from the north, with an ascending grade of one in one hundred, till within 618 feet of the bridge, after which the track is level; this leaves room for a train to stand between the grade and the bridge. The 2,380 feet of this approach, adjoining the bridge, is an open trestle work, thus making an effective water-way of 3,775 feet in times of extreme flood, when the bottom land is overflowed. The trestle is substantially built of native oak timber; the 50 bents nearest to the bridge rest on piles, and the others, 90 in number, are on sub-sills. on sub-sills. The roadway approach is by a side trestle, built out on the west from the bents of the railroad trestle; it has a grade of four in one hundred. The two approaches unite at the second bent from the bridge, where is placed a toll-house and gates. This trestle was built by the

See Plate IX.

Company at such intervals as the carpenters could be most advantageously employed upon it, in 1867 and 1868.

The carriage road was continued south of the bridge only far enough to allow teams to turn off into the adjoining streets. The railroad approach leaves the bridge on a 9° curve to the right, this curve beginning at the middle of the 132-foot span; with a maximum descending grade of 42.24 feet in a mile, it passes through the bluff in a clay cut 72 feet deep, and then passes down along a rock cut in the west side of the bluff to the depot grounds in the West Kansas bottom. The grading of this approach was let by contract and the work completed during the year 1867.

CHAPTER III.

FOUNDATIONS.

FROM the inception of the work the subject of foundations was the paramount study of the engineers, the only real difficulties of the task lying below the water. The methods of founding which have been in most common use in the United States were not to be thought of, as the continual wash and scour of the river would have made piles and crib-work useless, while the great depth and rapid current must have rendered coffer-dams very hazardous and expensive. The use of iron columns, sunk by the pneumatic process, was considered; but the conviction was early and confidently formed that a cluster of separate columns resting upon the rock at a depth but little below the scour limit, as would have been the case in the most exposed foundations at this location, would fail to give the stability needed by the channel piers; while it was believed that the sand-bar piers, which are rarely exposed to a strong current, might be founded in a way less expensive, though amply secure. It was also feared that in the absence of pneumatic plant in America, and with the then high prices of iron work, the pneumatic process would prove in its entire execution an unreasonably expensive one.

The opposite action of floods on the two sides of the river, causing a violent scour along the Kansas City shore where the channel lies, but a sand deposit near the north bank, showed that the precautions necessary for the channel piers would be a useless expense if taken at every foundation. The channel must be retained near the south bank on account of the draw, if for no other reason-thus rendering this phenomenon of scour and deposit a permanent one, subject only to such variations as are due to the increased width of channel in an extreme flood. It was therefore thought that if the channel