Amending the Map.—When the tiles are laid, and before they are covered, all deviations of the lines, as in passing around large stones and other obstructions, which may have prevented the exact execution of the original plan, and the location and kind of each underground silt-basin should also be carefully noted, so that they may be transferred to the map, for future reference, in the event of repairs becoming necessary. In a short time after the work[pg 143] is finished, the surface of the field will show no trace of the lines of drain, and it should be possible, in case of need, to find any point of the drains with precision, so that no labor will be lost in digging for it. It is much cheaper to measure over the surface than to dig four feet trenches through the ground.
CHAPTER V. - HOW TO TAKE CARE OF DRAINS AND DRAINED LAND.
So far as tile drains are concerned, if they are once well laid, and if the silt-basins have been emptied of silt until the water has ceased to deposit it, they need no care nor attention, beyond an occasional cleaning of the outlet brook. Now and then, from the proximity of willows, or thrifty, young, water-loving trees, a drain will be obstructed by roots; or, during the first few years after the work is finished, some weak point,—a badly laid tile, a loosely fitted connection between the lateral and a main, or an accumulation of silt coming from an undetected and persistent vein of quicksand,—will be developed, and repairs will have to be made. Except for the slight danger from roots, which must always be guarded against to the extent of allowing no young trees of the dangerous class to grow near a drain through which a constant stream of water flows, it may be fairly assumed that drains which have been kept in order for four or five years have passed the danger of interruption from any cause, and they may be considered entirely safe.
A drain will often, for some months after it is laid, run muddy water after rains. Sometimes the early deposit of silt will nearly fill the tile, and it will take the water of[pg 145] several storms to wash it out. If the tiles have been laid in packed clay, they cannot long receive silt from without, and that which makes the flow turbid, may be assumed to come from the original deposit in the conduit. Examinations of newly laid drains have developed many instances where tiles were at first half filled with silt, and three months later were entirely clean. The muddiness of the flow indicates what the doctors call "an effort of nature to relieve herself," and nature may be trusted to succeed, at least, until she abandons the effort. If we are sure that a drain has been well laid, we need feel no anxiety because it fails to take the water from the ground so completely as it should do, until it settles into a flow of clear water after the heaviest storms.
In the case of art actual stoppage, which will generally be indicated by the "bursting out" of the drain, i.e., the wetting of the land as though there were a spring under it, or as though its water had no underground outlet, (which is the fact,) it will be necessary to lay open the drain until the obstruction is found.
In this work, the real value of the map will be shown, by the facility which it offers for finding any point of any line of drains, and the exact locality of the junctions with the mains, and of the silt-basins. In laying out the plan on the ground, and in making his map, the surveyor will have had recourse to two or more fixed points; one of them, in our example, (fig. 21,) would probably be the center of the main silt-basin, and one, a drilled hole or other mark on the rock at the north side of the field. By staking out on the ground the straight line connecting these two points, and drawing a corresponding line on the map; we shall have a base-line, from which it will be easy, by perpendicular offsets, to determine on the ground any point upon the map. By laying a small square on the map, with one of its edges coinciding with the base-line, and moving it on this line until the other edge meets the[pg 146] desired point, we fix, at the angle of the square, the point on the base-line from which we are to measure the length of the offset. The next step is to find, (by the scale,) the distance of this point from the nearest end of the base-line, and from the point sought. Then measure off, in the field, the corresponding distance on the base-line, and, from the point thus found, measure on a line perpendicular to the base line, the length of the offset; the point thus indicated will be the locality sought. In the same manner, find another point on the same drain, to give the range on which to stake it out. From this line, the drains which run parallel to it, can easily be found, or it may be used as a base-line, from which to find, by measuring offsets, other points near it.
The object of this staking is, to find, in an inexpensive and easy way, the precise position of the drains, for which it would be otherwise necessary to grope in the dark, verifying our guesses by digging four-foot trenches, at random.
If there is a silt-basin, or a junction a short distance below the point where the water shows itself, this will be the best place to dig. If it is a silt-basin, we shall probably find that this has filled up with dirt, and has stopped the flow. In this case it should be cleaned out, and a point of the drain ten feet below it examined. If this is found to be clear, a long slender stick may be pushed up as far as the basin and worked back and forth until the passage is cleared. Then replace the tile below, and try with the stick to clean the tiles above the basin, so as to tap the water above the obstruction. If this cannot be done, or if the drain ten feet below is clogged, it will be necessary to uncover the tiles in both directions until an opening is found, and to take up and relay the whole. If the wetting of the ground is sufficient to indicate that there is much water in the drain, only five or six tiles should be taken up at a time, cleaned and relaid,—commencing at[pg 147] the lower end,—in order that, when the water commences to flow, it may not disturb the bottom of the ditch for the whole distance.