Draining for Profit, and Draining for Health Part 3

Fig. 5 - MAP WITH 50-FOOT SQUARES, AND CONTOUR LINES.

[Ill.u.s.tration: Fig. 5 - MAP WITH 50-FOOT SQUARES, AND CONTOUR LINES.]

Fig. 6 - LEVELLING INSTRUMENT.(4)

[Ill.u.s.tration: Fig. 7 - LEVELLING ROD.]

Fig. 7 - LEVELLING ROD.

The next operation is to trace, on the plan, lines following the same level, wherever the land is of the proper height for its surface to meet them. For the purpose of ill.u.s.trating this operation, lines at intervals of elevation of one foot are traced on the plan in Fig. 8. And these lines show, with sufficient accuracy for practical purposes, the elevation and rate of inclination of all parts of the field,-where it is level or nearly so, where its rise is rapid, and where slight. As the land rises one foot from the position of one line to the position of the line next above it, where the distance from one line to the next is great, the land is more nearly level, and when it is short the inclination is steeper. For instance, in the southwest corner of the plan, the land is nearly level to the 2-foot line; it rises slowly to the center of the field, and to the eastern side about one-fourth of the distance from the southern boundary, while an elevation coming down between these two valleys, and others skirting the west side of the former one and the southern side of the latter, are indicated by the greater nearness of the lines. The points at which the contour lines cross the section lines are found in the following manner: On the second line from the west side of the field we find the elevations of the 4th, 5th and 6th stakes from the southern boundary to be 1.9, 3.3, and 5.1. The contour lines, representing points of elevation of 2, 3, 4, and 5 feet above the _datum line_, will cross the 50-foot lines at their intersections, only where these intersections are marked in even feet. When they are marked with fractions of a foot, the lines must be made to cross at points between two intersections,-nearer to one or the other, according to their elevations,-thus between 1.9 and 3.3, the 2-foot and 3-foot contour lines must cross. The total difference of elevation, between the two points is 3.3-1.9=1.4; 10/14 of the s.p.a.ce must be given to the even foot between the lines, and the 2-foot line should be 1/14 of the s.p.a.ce above the point 1.9;-the 3-foot line will then come 3/14 below the point 3.3. In the same manner, the line from 3.3 to 5.1 is divided into 18 parts, of which 10 go to the s.p.a.ce between the 4. and 5. lines, 7 are between 3.3 and the 4-foot line, and 1 between the 5-foot line and 5.1.

[Ill.u.s.tration: Fig. 8 - MAP WITH CONTOUR LINES.]

Fig. 8 - MAP WITH CONTOUR LINES.

With these maps, made from observations taken in the field, we are prepared to lay down, on paper, our system of drainage, and to mature a plan which shall do the necessary work with the least expenditure of labor and material. The more thoroughly this plan is considered, the more economical and effective will be the work. Having already obtained the needed information, and having it all before us, we can determine exactly the location and size of each drain, and arrange, before hand, for a rapid and satisfactory execution of the work. The only thing that may interfere with the perfect application of the plan, is the presence of ma.s.ses of underground rock, within the depth to which the drains are to be laid.(5) Where these are supposed to exist, soundings should be made, by driving a 3/4-inch pointed iron rod to the rock, or to a depth of _five_ feet where the rock falls away. By this means, measuring the distance from the soundings to the ranges of the stakes, we can denote on the map the shape and depth of sunken rocks. The shaded spot on the east side of the map, (Fig. 8,) indicates a rock three feet from the surface, which will be a.s.sumed to have been explored by sounding.

In most cases, it will be sufficient to have contour lines taken only at intervals of two feet, and, owing to the smallness of the scale on which these maps are engraved, and to avoid complication in the finished plan, where so much else must be shown, each alternate line is omitted. Of course, where drains are at once staked out on the land, by a practiced engineer, no contour lines are taken, as by the aid of the level and rod for the flatter portions, and by the eye alone for the steeper slopes, he will be able at once to strike the proper locations and directions; but for one of less experience, who desires to thoroughly mature his plan before commencing, they are indispensable; and their introduction here will enable the novice to understand, more clearly than would otherwise be possible, the principles on which the plan should be made.

[Ill.u.s.tration: Fig. 9 - WELL'S CLINOMETER.]

Fig. 9 - WELL'S CLINOMETER.

For preliminary examinations, and for all purposes in which great accuracy is not required, the little instrument shown in Fig. 9,-"Wells'

Clinometer,"-is exceedingly simple and convenient. Its essential parts are a flat side, or base, on which it stands, and a hollow disk just half filled with some heavy liquid. The gla.s.s face of the disk is surrounded by a graduated scale that marks the angle at which the surface of the liquid stands, with reference to the flat base. The line 0.--0. being parallel to the base, when the liquid stands on that line, the flat side is horizontal; the line 90.--90. being perpendicular to the base, when the liquid stands on that line, the flat side is perpendicular or _plumb_. In like manner, the intervening angles are marked, and, by the aid of the following tables, the instrument indicates the rate of fall per hundred feet of horizontal measurement, and per hundred feet measured upon the sloping line.(6)

Table No. 1 shows the rise of the slope for 100 feet of the horizontal measurement. Example: If the horizontal distance is 100 feet, and the slope is at an angle of 15, the rise will be 17-633/1000 feet.

Table No. 2 shows the rise of the slope for 100 feet of its own length. If the sloping line, (at an angle of 15,) is 100 feet long, it rises 25.882 feet.

TABLE No. 1.

DEG. FEET.

5 8.749 10 17.663 15 26.795 20 36.397 25 46.631 30 57.735 35 70.021 40 83.910 45 100.- 50 119.175 55 142.815 60 173.205 65 214.451 70 274.748 75 373.205 80 567.128 85 1143.01

TABLE No. 2 DEG. FEET.

5 8.716 10 17.365 15 25.882 20 34.202 25 42.262 30 50.- 35 57.358 40 64.279 45 70.711 50 76.604 55 81.915 60 86.602 65 90.631 70 93.969 75 96.593 80 98.481 85 99.619

With the maps before him, showing the surface features of the field, and the position of the under-ground rock, the drainer will have to consider the following points:

1. Where, and at what depth, shall the outlet be placed?

2. What shall be the location, the length and the depth of the main drain?

3. What subsidiary mains,-or collecting drains,-shall connect the minor valleys with the main?

4. What may best be done to collect the water of large springs and carry it away?

5. What provision is necessary to collect the water that flows over the surface of out-cropping rock, or along springy lines on side hills or under banks?

6. What should be the depth, the distance apart, the direction, and the rate of _fall_, of the lateral drains?

7. What kind and sizes of tile should be used to form the conduits?

8. What provision should be made to prevent the obstruction of the drains, by an acc.u.mulation of silt or sand, which may enter the tiles immediately after they are laid, and before the earth becomes compacted about them; and from the entrance of vermin?

1. The outlet should be at the lowest point of the boundary, unless, (for some especial reason which does not exist in the case under consideration, nor in any usual case,) it is necessary to seek some other than the natural outfall; and it should be deep enough to take the water of the main drain, and laid on a sufficient inclination for a free flow of the water. It should, where sufficient fall can be obtained without too great cost, deliver this water over a step of at least a few inches in height, so that the action of the drain may be seen, and so that it may not be liable to be clogged by the acc.u.mulation of silt, (or mud,) in the open ditch into which it flows.

2. The main drain should, usually, be run as nearly in the lowest part of the princ.i.p.al valley as is consistent with tolerable straightness. It is better to cut across the point of a hill, to the extent of increasing the depth for a few rods, than to go a long distance out of the direct course to keep in the valley, both because of the cost of the large tile used in the main, and of the loss of fall occasioned by the lengthening of the line. The main should be continued from the outlet to the point at which it is most convenient to collect the more remote sub-mains, which bring together the water of several sets of laterals. As is the case in the tract under consideration, the depth of the main is often restricted, in nearly level land, toward the upper end of the flat which lies next to the outlet, by the necessity for a fall and the difficulty which often exists in securing a sufficiently low outlet. In such case, the only rule is to make it as deep as possible. When the fall is sufficient, it should be placed at such depth as will allow the laterals and sub-mains which discharge into it to enter at its top, and discharge above the level of the water which flows through it.

[Ill.u.s.tration: Fig. 10 - STONE PIT TO CONNECT SPRING WITH DRAIN.]

Fig. 10 - STONE PIT TO CONNECT SPRING WITH DRAIN.

3. Subsidiary mains, or _sub-mains_, connecting with the main drains, should be run up the minor valleys of the land, skirting the bases of the hills. Where the valley is a flat one, with rising ground at each side, there should be a sub-main, to receive the laterals from _each_ hill side.

As a general rule, it may be stated, that the collecting drain at the foot of a slope should be placed on the line which is first reached by the water flowing directly down over its surface, before it commences its lateral movement down the valley; and it should, if possible, be so arranged that it shall have a uniform descent for its whole distance. The proper arrangement of these collecting drains requires more skill and experience than any other branch of the work, for on their disposition depends, in a great measure, the economy and success of the undertaking.

4. Where springs exist, there should be some provision made for collecting their water in pits filled with loose stone, gravel, brush or other rubbish, or furnished with several lengths of tile set on end, one above the other, or with a barrel or other vessel; and a line of tile of proper size should be run directly to a main, or sub-main drain. The manner of doing this by means of a pit filled with stone is shown in Fig. 10. The collection of spring water in a vertical tile basin is shown in Fig. 11.

[Ill.u.s.tration: Fig. 11 - STONE AND TILE BASIN FOR SPRING WITH DRAIN.]

Fig. 11 - STONE AND TILE BASIN FOR SPRING WITH DRAIN.

5. Where a ledge of shelving rock, of considerable size, occurs on land to be drained, it is best to make some provision for collecting, at its base, the water flowing over its surface, and taking it at once into the drains, so that it may not make the land near it unduly wet. To effect this, a ditch should be dug along the base of the rock, and _quite down to it_, considerably deeper than the level of the proposed drainage; and this should be filled with small stones to that level, with a line of tile laid on top of the stones, a uniform bottom for the tile to rest upon being formed of cheap strips of board. The tile and stone should then be covered with inverted sods, with wood shavings, or with other suitable material, which will prevent the entrance of earth, (from the covering of the drain,) to choke them. The water, following down the surface of the rock, will rise through the stone work and, entering the tile, will flow off.

This method may be used for springy hill sides.

6. The points previously considered relate only to the collection of unusual quant.i.ties of water, (from springs and from rock surfaces,) and to the removal from the land of what is thus collected, and of that which flows from the minor or lateral drains.

The _lateral drains_ themselves const.i.tute the real drainage of the field, for, although main lines take water from the land on each side, their action in this regard is not usually considered, in determining either their depth or their location, and they play an exceedingly small part in the more simple form of drainage,-that in which a large tract of land, of perfectly uniform slope, is drained by parallel lines of equal length, all discharging into a single main, running across the foot of the field. The land would be equally well drained, if the parallel lines were continued to an open ditch beyond its boundary,-the main tile drain is only adopted for greater convenience and security. It will simplify the question if, in treating the _theory_ of lateral drains, it be a.s.sumed that our field is of this uniform inclination, and admits of the use of long lines of parallel drains. In fact, it is best in practice to approximate as nearly as possible to this arrangement, because deviations from it, though always necessary in broken land, are always more expensive, and present more complicated engineering problems. If all the land to be drained had a uniform fall, in a single direction, there would be but little need of engineering skill, beyond that which is required to establish the depth, fall, and distance apart, at which the drains should be laid. It is chiefly when the land pitches in different directions, and with varying inclination, that only a person skilled in the arrangement of drains, or one who will give much consideration to the subject, can effect the greatest economy by avoiding unnecessary complication, and secure the greatest efficiency by adjusting the drains to the requirements of the land.

a.s.suming the land to have an unbroken inclination, so as to require only parallel drains, it becomes important to know how these parallel drains, (corresponding to the _lateral drains_ of an irregular system,) should be made.

The history of land draining is a history of the gradual progress of an improvement, from the accomplishment of a single purpose, to the accomplishment of several purposes, and most of the instruction which modern agricultural writers have given concerning it, has shown too great dependence upon the teachings of their predecessors, who considered well the single object which they sought to attain, but who had no conception that draining was to be so generally valuable as it has become. The effort, (probably an unconscious one,) to make the theories of modern thorough-draining conform to those advanced by the early pract.i.tioners, seems to have diverted attention from some more recently developed principles, which are of much importance. For example, about a hundred years ago, Joseph Elkington, of Warwicks.h.i.+re, discovered that, where land is made too wet by under-ground springs, a skillful tapping of these,-drawing off their water through suitable conduits,-would greatly relieve the land, and for many years the Elkington System of drainage, being a great improvement on every thing theretofore practiced, naturally occupied the attention of the agricultural world, and the Board of Agriculture appointed a Mr. Johnstone to study the process, and write a treatise on the subject.

Catch-water drains, made so as to intercept a flow of surface water, have been in use from immemorial time, and are described by the earliest writers. Before the advent of the Draining Tile, covered drains were furnished with stones, boards, brush, weeds, and various other rubbish, and their good effect, very properly, claimed the attention of all improvers of wet land. When the tile first made its appearance in general practice, it was of what is called the "horse-shoe" form, and,-imperfect though it was,-it was better than anything that had preceded it, and was received with high approval, wherever it became known. The general use of all these materials for making drains was confined to a system of _partial_ drainage, until the publication of a pamphlet, in 1833, by Mr.

Smith, of Deanston, who advocated the drainage of the whole field, without reference to springs. From this plan, but with important modifications in matters of detail, the modern system of tile draining has grown. Many able men have aided its progress, and have helped to disseminate a knowledge of its processes and its effects, yet there are few books on draining, even the most modern ones, which do not devote much attention to Elkington's discovery; to the various sorts of stone and brush drains; and to the manufacture and use of horse-shoe tile;-not treating them as matters of antiquarian interest, but repeating the instructions for their application, and allowing the reasoning on which their early use was based, to influence, often to a damaging extent, their general consideration of the modern practice of tile draining.

These processes are all of occasional use, even at this day, but they are based on no fixed rules, and are so much a matter of traditional knowledge, with all farmers, that instruction concerning them is not needed. The kind of draining which is now under consideration, has for its object the complete removal of all of the surplus water that reaches the soil, from whatever source, and the a.s.similation of all wet soils to a somewhat uniform condition, as to the ease with which water pa.s.ses through them.

There are instances, as has been shown, where a large spring, overflowing a considerable area, or supplying the water of an annoying brook, ought to be directly connected with the under-ground drainage, and its flow neatly carried away; and, in other cases, the surface flow over large ma.s.ses of rock should be given easy entrance into the tile; but, in all ordinary lands, whether swamps, springy hill sides, heavy clays, or light soils lying on retentive subsoil, all ground, in fact, which needs under-draining at all, should be laid dry above the level to which it is deemed best to place the drains;-not only secured against the wetting of springs and soakage water, but rapidly relieved of the water of heavy rains. The water table, in short, should be lowered to the proper depth, and, by permanent outlets at that depth, be prevented from ever rising, for any considerable time, to a higher level. This being accomplished, it is of no consequence to know whence the water comes, and Elkington's system need have no place in our calculations. As round pipes, with collars, are far superior to the "horse-shoe" tiles, and are equally easy to obtain, it is not necessary to consider the manner in which these latter should be used,-only to say that they ought not to be used at all.

The water which falls upon the surface is at once absorbed, settles through the ground, until it reaches a point where the soil is completely saturated, and raises the general water level. When this level reaches the floor of the drains, the water enters at the joints and is carried off.