DRAINING LAND.

Lyttelton Times, Volume XXIII, Issue 1415, 20 June 1865, Page 5

DRAINING LAND.

We extract the following instructive passage from one of a series of able lectures recently delivered before the Uoyal Agricultural College (England) by Mr. Wallace Fyfe

Levelling.—The outfall is the first thing to be determined in drainage. The leading object is to secure a sufficient natural outfall from the leading or main drain. Fortunately water will flow on the very slightest incline, and there are very few situations in which a suitable outfall is not found, if only of two inches in 100 yards—for that in default of better will suffice. This dip or declination is so small that many agriculturists, although possessed of sufficient outfall, are often found harboring the mistake that drainage is for them a thing impossible, when it is nothing of the sort. The eye, too, is often deceptive in regard to the ground level; and the use of instruments alone can determine the true state of the case,

Levelling is the easiest and most elementary task n surveying; yet it is one requiring the utmost licety and attention. Various kinds of levels are lonstantly employed in setting-off or finding the evels for drains. But in order to test the fall, cut he drain accurately and uniformly before laying in he tiles and other materials ; three staves, _ two of >qual length, about two feet, and one to suit itself in ;he drain to the height of these, having at one end jross pieces of wood nine inches in length, are comnonly employed where the ground is tolerably flat, md answer well when the drain is straight, though lot when it is curved. The drain being first cut to ;he proper depth as far as the eye can judge, one short staff is held perpendicularly on the ground at ;he upper, and another at the lower end of the drain, whilst the other staff, adjusted to stand at the correct height' of the other two above the drain bottom, is moved along from one end to the other; the surveyor, it one end of the drain, bringing his eye down into the line with the upper edge of the cross-beads on the staves, notices whether or not that of the long staff keeps the eye line. According as in moving it iilong he perceives it rise above or sink below this line, the bottom of the drain must be altered so as to make the three cross-heads coincide. Care must, however, be taken 'to ascertain that the bottom does slope in the right direction, as these staves only test its regularity, not its inclination. Staves painted in strong contrast of colours are the most readily distinguishable. . The mason's plumb-level forms a very convenient instrument for the use of drainers. By making a mark as fiir off the plumb line as will subtend an angfcequal to the intended fall of thedrain, the leveller can always keep to the angle of inclination of the fall. Thompson's Workman's Level is an instrument calculated to enable drains to be carried out on a uniform slope. It differs only from the mason s plumb-level in having the uprights capable of being lengthened or shortened by shifting the hypothenuse, so that it will form any required angle with the base. There is an index head on which the rate of slope is indicated on a graduated scale ; and the instrument is kept at any given point by tightening a nut at the index head. The instrument when in use is set in the slope of the drain, and all the workman has to do is to see that the plumb lino strikes the centre. Gillesoie's patent inclinometer carries out the same principle by extending it from u triangle to ft full parallelogram. In fact, when I first saw them applying it in levelling the drains on his estate of Tirbane Hill, I really thought the machine was composed of the four spars of a common field gate, with a diagonal moving upon pins, which made the bottom spar down in the drain parallel with the top spar seen above it, when set to the required inclination. I thought the instrument very effective,but ridiculously simple. But by the time it passed through the hands of the Patent Office, and I was called upon by the inventor to write the accompanying descriptive pamphlet which is issued with it by the makers, I found it had become quite complicated since I first saw it in its field-gate form ; the top parallel necessarily represented to the eye the amount und direction of the slope, but now an additional

limb or parallel was hinged at one end to the top bar, and from the other end depended a plummet. In action, the moveable limb had to be raised from its parallel position to one perfectly horizontal, as indicated by the plummet, and thus marked the rate of slope on an index spirit level, which is placed in a japanned frame with braßs graduated arch, and mounted on a tripod stand, with levelling screws to bring it into adjustment. To this is adapted an iron frame carrying two sights with cross hairs, capable of turning round on a centre, and of being raised or lowered at pleasure. The rate of rise or fall is ascertained on inspection. By levelling and traversing the instrument in the plane of the horizon, it will also indicate the most favourable fall. The cost, with tripod stand, is £1 18s. Gravatt's " Dumpy" level is more popular amongst surveyors, but it is principally employed where the levels require to be continued for miles, arid the height of one point aboveanotherdetermined to an inch, as in the case of railway*. This level would be found useful where it became necessary to conduct water from a spring head to a considerable distance. All that the surveyor would have to do would be to determine whether the level of the fountain head was above that of the place to which the water had to be abandoned, for if higher the water would assuredly find its way in pipes, however rugged the intervening surface, care being always taken to guard at any point against too abrupt a fall, since the water might otherwise rush in too rapid a current; and thus it is better that the pipes should be laid more nearly to the level or even in a curve, so as to produce the same effect; pipes being sometimes directed even a little upwards before approaching the point of discharge, to restrain the velocity of the current.

Main drains or ditches on level lands should always be directed as straight as possible—a feat which gives no trouble to experienced drainers. "A good ploughman," said Mr. Pusey, in that superb report of his already quoted, " will set up a pole a quarter of a mile distant or more, and keeping this mark, almost invisible, steadily in his view, will, on land perfectly smooth, trace up to that goal, until his horses knock it they pass down as on each side, a furrow so true that no eye can trace any divergence from absolute straightness." Such is theabsolute skill, fast dying out, however (?), which distinguishes the agricultural labourer. The difference betwixt a straight drain and a crooked one tells powerfully on the rate of outfall. Thus, in scouring an old watercourse of 1200 feet long, with a fall of one inch in 100 feet, it was found that a new course, measuring only 800 feet long, might be executed, and the rate of inclination consequently increased half an inch in the 100 feet. But whether straightened or not the outfalls from main drains should be regularly secured, and the months of the leading drains kept clear of all obstructions ; instead of the old indolent practice of allowing the ditches to become nearly choked before being cleaned, by simply scouring the ditches often, and never permitting them to become deeply filled with mud, the keeping them in order is found to cost a mere unfelt trifle, compared with the huge task of cleansing them after long neglect, besides supplying a peculiar covering for the compost heaps formed at various periods, which, as we shall see when we come to treat of the economy of manures, is an essential object in fixing and retaining their volatile constituents—and pond and ditch mud, though valuable when thus applied, is really of very little importance. Where, however, you happen to have a thing, and it has a value, I am a great advocate for using it up on a farm, whatever that value may be. The great reason, however, for scouring your outfalls is, that you may not literally be found undoing at that point what it has been the sole object of your drainage to effect. The essential point in drainage is that water should never be suffered to remain stagnant, either in or out of the drains ; indeed, the drains themselves will never draw efficiently whilst their outlet remains imperfect. In like manner, to secure a free' flow at all times from the smaller drains, outfalls and main drains must alike be rendered perfect. So important has this been judged, even in a national point of view, that the Act 10 and 11 Victoria, c. 30, was passed for no other purpose than to facilitate improvements by way of drainage, and to empower owners of property, under certain conditions and restrictions, to enter upon lands belonging to other owners to obtain outfalls. It is true that, by section 9, no entry is to be made on any land for these purposes, except with the consent of the proprietors, until the amount of compensation for damage shall have been agreed upon or ascertained and paid ; still the right of obtaining an outfall, even upon payment, is a powerful recognition of the ralue and importance of drainage improvements.