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first dikes built should be such as to cause the raising of the bottom of the chute only a few feet. Then after a year or so, on the deposits first made, new structures should be built, and so on.

As the closing of chutes by natural means is usually due to the closing in of the sides, dikes intended to artificially produce similar results should be built so as to encourage the growth of the bars

along the side of the chute; that is, the dike should generally be % higher, though not necessarily taller, over these bars than in the

middle of the chute, and in most cases probably less pervious,

After the closing of the chute has gone on to some considerable extent and large deposits have been made in it, and the bars on its side have grown high and become covered with willows, further work will not be needed, for as the chute closes up the frictional resistance to the flow of water through it will increase, and consequently the velocity of the flow through it during floods will decrease, and after a while these functions will be so related that the chute will tend to close itself and may be left alone. The object of closing a chute is to concentrate the water in the main river principally when the bars formed in the main channel during high water are being cut into the low-water channel, and this will usually be accomplished if the chute be closed below about mid-stage. Consequently, when that has been done, no further work will be needed except to insure against the reopening of the chute and, of course, the surest way to do this is to leave the chute in such a condition that the natural tendency is to a further closure.

As to the form of dike to be used, the conclusions are not so certain; pile dikes have not for such uses been thoroughly successful, and the triangular frame dikes have not been tried in such localities. Judging, however, from the action of such dikes in other localities, it is believed that the best form of dike for use in long chutes is a modification of the triangular framed dikes.

The trouble with the pile dikes was their tendency to catch drift, and this the triangular frame dikes are planned to avoid. Pile dikes have a vertical upstream side, and as a result drift has no tendency to slide over them, while the waling pieces and braces serve to catch the projecting branches and roots and thus hold the drift. The framed dikes, on the other hand, by their gentle upstream slope tend to deflect the drift upward and allow it to slide over them; there are in front of the screens no horizontal stringers or waling pieces to catch on the limbs and roots, and the screen has no opening large enough to permit limbs of any size to slip through

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part of the work must be built dry and that the material must be transported from the river, probably about $5 per linear foot, and as in chutes the size of Gold Dust the dikes must be nearly 2,000 feet long, and as to be really effectual a number of them must be used, and as the first dikes will only cause a partial closing of the chute and must be supplanted later by additional structures, it is evident that the closure of such chutes will not be the easy and inexpensive operation it was at first thought.

1

PART II

BANK REVETMENT

The immediate object of bank revetment is to protect the bank of the river from erosion and destruction by the current. The manner in which the current acts in cutting and caving away the banks has already been described.

The work of revetting banks has been extensively carried on by the Commission in these districts, and a history of its development and progress will now be attempted. This description would, however, not be complete without a reference to some work of the same character started at Memphis before the organization of the Commission.

This history, except the parts relating to Plum Point Reach, has
been largely compiled and written by Assistant Engineer W. M.
Rees, who has been connected with the construction work under the
Memphis office since 1882.

EARLY REVETMENT WORK IN MEMPHIS HARBOR

Active caving of the bank along the Memphis river front began in the early seventies, and by 1879 this rapid caving was seriously endangering the many important business, manufacturing, and railroad interests located along the river. (Plate XXIV.)

The first project for the protection of this bank was made in 1877 by Maj. W. II. H. Benyaurd, the engineer officer stationed at Memphis. This project contemplated the continuous revetment of the bank with brush mattresses ballasted with stone, to extend from the mouth of Wolf River down to the foot of Jefferson street and from the mouth of Wolf River upstream a distance of about 2,000 feet; this protection to extend from the greatest depth to a short distance above the low-water mark. The estimated cost of the work was $170,000. Under this project work was begun in 1878 and continued at each low-water season until the close of 1882; the aggregate of the appropriations and allotments being $138,000.

For the construction of the mattresses ways were built along the sloping bank of Wolf River. They were 200 feet long and 75 feet wide. The stringers had an inclination of about 4 inches to a foot

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and were spaced 5 feet apart. The materials used in the construction of the mattress were cottonwood poles of 4 to 5 inches in . diameter and straight, green willow brush of 1 to 2 inches in diameter.

The method of mattress construction was as follows: Lines of poles were placed across and at right angles to the ways every 4 feet, and across these and at right angles to these were placed similar poles, also spaced 4 feet apart, and these were joined at their intersection by three-fourth-inch oak pins 9 inches long. On this grillage was placed three alternating layers of brush, and on top a pole framework similar to the bottom grillage, the two being united at every 8 feet with oak rods 1 inch in diameter and 4 feet long passing through both frames, the brush being well compressed before the rods were secured. In addition to the rod connections the frames were joined to each other by wire ties.

The mattresses were about 3 feet thick, 50 feet wide, and from 100 to 150 feet long.

When completed and launched, they were brought to place by a tug and anchored with their lengths normal to the bank. Lines were run from them to fastenings on the bank above, and also to the bank below where necessary to steady them in a reverse or eddy current. Flats loaded with stone ballast were placed around the mattress, and the ballast cast on until they sank. Considerable care had to be exercised in the matter of ballasting to sink properly and to prevent breaking, and after some experience lines from the flats were used to guide the mats to the bottom. Of the twentythree mats sunk during the season of 1878 three had about 30 feet each broken off their outstream ends during the sinking process. Sometimes, before any ballast was placed, the strong current would strike the upper side and drive the mat some distance under the water; then its buoyancy would assert itself and bring it to the surface, and in this way some of the mats were broken before the ballasting had been begun.

SEASON OF 1878

The first mat, 125 by 50 by 3 feet, was launched August 8, 1878, and the second a week later. After these were sunk, the breaking out of yellow fever caused a suspension until November 7, when work was resumed. Later in the season there was another interruption due to high water, and on the subsidence of this the work was a second time resumed.

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