Imágenes de páginas
PDF
EPUB

Bd. They should, as nearly as possible, run parallel to each other.

On land of perfectly uniform character, (all sloping in the same direction,) all of these requirements may be complied with, but on irregular land it becomes constantly necessary to make a compromise between them. Drains running down the line of steepest descent cannot be parallel,-and, consequently, the intervals between them cannot be always the same; those which are farther apart at one end than at the other cannot be always of a depth exactly proportionate to their intervals.

In the adjustment of the lines, so as to conform as nearlý to these requirements as the shape of the ground will allow, there is room for the exercise of much skill, and on such adjustment depend, in a great degree, the success and économy of the work. Remembering that on the map, the line of steepest descent is exactly perpendicular to the contour lines of the land, it will be profitable to study carefully the system of drains first laid out, erasing and making alterations wherever it is found possible to simplify the arrangement. . .

Strictly speaking, all angles are, to a certain extent, wasteful, because, if two parallel drains will suffice to drain the land between them, no better drainage will be effected by a third drain running across that land. Furthermore the angles are practically supplied with drains at less in. tervals than are required,—for instance, at C 7a on the map the triangles included within the dotted line x, y, will be doubly drained. So, also, if any point of a 4-foot drain will drain the land within 20 feet of it, the land included within the dotted line forming a semi-circle about the point C14, might drain into the end of the lateral, and it no more needs the action of the main drain than does that which lies between the laterals..! Of course, angles and connecting lines are in. dispensable, except where the laterals can run in de

pendently across the entire field, and discharge beyond its The longer the laterals can be made, and the more anglen can be avoided, the more economical will the arrangement be; and, until the arrangement of the lines has been made as nearly perfect as possible, the time of the drainer can bu in no way so profitably spent as in amending his plan.

The series of laterals which discharge through the mains A, C, D and E, on the accompanying map, have been very carefully considered, and are submitted to the consideration of the reader, in illustration of what has been said above.

At one point, just above the middle of the east side of the field, the laterals are placed at a general distance of 20 feet, because, as will be seen by reference to Fig. 4, a ledge of rock, underground, will prevent their being made more than 3 feet deep.

The line from H to I, (Fig. 20,) at the north side of the field, connecting the heads of the laterals, is to be a stone and tile drain, such as is described on page 60, intended to collect the water which follows the surface of the rock. (See Fig. 4.)

The swamp is to be drained by itself, by means of two series of laterals discharging into the main lines Fand G, which discharge at the outlet, by the side of the main drain from the silt-basin. By this arrangement, these laterals, especially at the north side of the swamp, being accurately laid, with very slight inclinations, can be placed more deeply than if they ran in an east and west direction, and discharged into the main, which has a greater inclination, and is only two and a half feet deep at the basin. Being 3; (3.50) feet deep at the outlet, they may be made fully 3 feet deep at their upper ends, and, being only 20 feet apart, they will drain the land as well as is possible. The drains being now laid out, over the whole Geld, the next thing to be attended to is

The Ordering of the Tile.—The main line from the outlet ap to the silt-basin, should be of 3 -inch tiles, of which about 190 feet will be required. The main drain A should be laid with 24inch tiles to the point marked m, near its upper end, as the lateral entering there carries the water of a spring, which is supposed to fill a 14-inch tile. The length of this drain, from the silt-basin to that point is 575 feet. The main drain C will require 4 inch tiles from the silt-basin to the junction with the lateral, which is marked C 10, above which point there is about 1,700 feet of drain discharging into it, a portion of which, being a stone-and-tile drain at the foot of a rock, may be supposed to receive more water than that which lies under the rest of the land ;-distance 450 feet. The main drain E requires 27-inch tiles from the outlet to the point marked 0, a distance of 380 feet. This tile will, in addition to its other work, carry as much water from the spring, on the line of its fourth lateral, as would fill a 14-inch pipe.*

The length of the main drains above the points indi. cated, and of all the laterals, amounts to about 12,250 feet These all require 14-inch tiles.

Allowing about five per cent. for breakage, the order is . round numbers, will be as follows:

37-inch round tiles • • • • • 200 feet.
27 66 66 66 . . . . . 1,500 6
1 66 66 66 . . . . . . 13,000 66

Collars ...... 1,600

u . . . . . . 13,250

* If the springs, when running at their greatest volume, be found to require more than 1-inch tiles, due allowance must be made for the increase. · + Owing to the irregularity of the ground, and the necessity for placing some of the drains at narrower intervals, the total length of tile exceeds by nearly 50 per cent. what would be required if it had a uniform slope, and required no collecting drains. It is much greater than will be required in any ordinary case, as a very irregular surfach and Doon adostad boro for porposes of illustration.

Order, also, 25 6-inch sole-tiles, to be used in making small silt-basins.

It should be arranged to have the tiles all on the ground before the work of ditching commences, so that there may be no delay and consequent danger to the stability of the banks of the ditches, while waiting for them to arrive. As has been before stated, it should be especially agreed with the tile-maker, at the time of making the contract, that every tile should be perfect;--of uniform shape, and neither too much nor too little burned.

Staking Out.-Due consideration having been given to such preliminaries as are connected with the mapping of the ground, and the arrangement, on paper, of the drains to be made, the drainer may now return to his field, and, while awaiting the arrival of his tiles, make the necessary preparation for the work to be done. The first step is to fix certain prominent points, which will serve to connect the map with the field, by actual measurements, and this will very easily be done by the aid of the stakes which are still standing at the intersections of the 50-foot lines, which were used in the preliminary levelling.

Commencing at the southwest corner of the field, and measuring toward the east a distance of 34 feet, set a pole to indicate the position of the outlet. Next, mark the center of the silt-basin at the proper point, which will be found by measuring 184 feet up the western boundary, and thence toward the east 96 feet, on a line parallel with the nearest row of 50-foot stakes. Then, in like manner, fix the points C 1, C6, C9, C 10, and C 17, and the angles of the other main lines, marking the stakes, when placed, to correspond with the same points on the map. Then stake the angles and the upper ends of the laterals, and mark these stakes to correspond with the map.

It will greatly facilitate this operation, if the plan of the drains which is used in the field, from which the hori

the the other main th the same poinds of the li

[ocr errors]

zontal lines should be omitted, have the intersecting 50 foot lines drawn upon it, so that the measurements may be made from the nearest points of intersection.*

Having staked these guiding points of the drains, it is advisable to remove all of the 50-foot stakes, as these are of no further use, and would only cause confusion. It will now be easy to set the remaining stakes,-placing one at every 50 feet of the laterals, and at the intersections of all the lines.

B ut I'. A system for marking the stakes is indicated on the map, (in the C series of drains,) which, to avoid the confusion wbich would result from too much detail on such a small scale, has been carried only to the extent necessary for illustration. The stakes of the line C are marked Ci, C2, C3, etc. The stakes of the sub-main C7, are marked c7a, C76, C7c, etc. The stakes of the lateral which enters this drain at cya, are marked C 7a, Cra, 07a, eto. etc. This system, which connects the lettering of each lateral with its own sub-main and main, is perfectly sim ple, and avoids the possibility of confusion. The position of the stakes should all be lettered on the map, at the original drawing, and the same designating marks put on the stakes in the field, as soon as set. * Grade Stakes, (pegs about 8 or 10 inches long,) should be placed close at the sides of the marked stakes, and driven nearly their full length into the ground. The topg of these stakes furnish fixed points of elevation from which to take the measurements, and to make the compu. tations necessary to fix the depth of the drain at each stake. If the measurements were taken from the surface of the ground, a slight change of position in placing the instrument, would often make a difference of some inches in the depth of the drain.

*The stakes used may be 18 inches long, and driven one-half of their length into the ground. They should have one side suficiently smooth to be distinctly marked with red chalk.

« AnteriorContinuar »