Chapter III: How to Go to Work to Lay Out a System of Drains (2)

The more important reasons why this direction is the best are the following: First, it is the quickest way to get the water off. Its natural tendency is to run straight down the hill, and nothing is gained by diverting it from this course. Second, if the drain runs obliquely down the hill, the water will be likely to run out at the joints of the tile and wet the ground below it; even if it do not, mainly, run past the drain from above into the land below, instead of being forced into the tile. Third, a drain lying obliquely across a hillside will not be able to draw the water from below up the hill toward it, and the water of nearly the whole interval will have to seek its outlet through the drain below it. Fourth, drains running directly down the hill will tap any porous water bearing strata, which may crop out, at regular intervals, and will thus prevent the spewing out of the water at the surface, as it might do if only oblique drains ran for a long distance just above or just below them. Very steep, and very springy hill sides, sometimes require very frequent drains to catch the water which has a tendency to flow to the surface; this, however, rarely occurs.

In laying out a plan for draining land of a broken surface, which inclines in different directions, it is impossible to make the drains follow the line of steepest descent, and at the same time to have them all parallel, and at uniform distances. In all such cases a compromise must be made between the two requirements. The more nearly the parallel arrangement can be preserved, the less costly will the work be, while the more nearly we follow the steepest slope of the ground, the more efficient will each drain be. No rule for this adjustment can be given, but a careful study of the plan of the ground, and of its contour lines, will aid in its determination. On all irregular ground it requires great skill to secure the greatest efficiency consistent with economy.

The _fall_ required in well made tile drains is very much less than would be supposed, by an inexperienced person, to be necessary. Wherever practicable, without too great cost, it is desirable to have a fall of one foot in one hundred feet, but more than this in ordinary work is not especially to be sought, although there is, of course, no objection to very much greater inclination.

One half of that amount of fall, or six inches in one hundred feet, is quite sufficient, if the execution of the work is carefully attended to.

The least rate of fall which it is prudent to give to a drain, in using ordinary tiles, is 2.5 in 1,000, or three inches in one hundred feet, and even this requires very careful work.(8) A fall of six inches in one hundred feet is recommended whenever it can be easily obtained--not as being more effective, but as requiring less precision, and consequently less expense.

*Kinds and Sizes of Tiles.*--Agricultural drain-tiles are made of clay similar to that which is used for brick. When burned, they are from twelve inches to fourteen inches long, with an interior diameter of from one to eight inches, and with a thickness of wall, (depending on the strength of the clay, and the size of the bore,) of from one-quarter of an inch to more than an inch. They are porous, to the extent of absorbing a certain amount of water, but their porosity has nothing to do with their use for drainage,--for this purpose they might as well be of glass. The water enters them, not through their walls, but at their joints, which cannot be made so tight that they will not admit the very small amount of water that will need to enter at each space. Gisborne says:

"If an acre of land be intersected with parallel drains twelve yards apart, and if on that acre should fall the very unusual quantity of one inch of rain in twelve hours, in order that every drop of this rain may be discharged by the drains in forty-eight hours from the commencement of the rain--(and in a less period that quantity neither will, not is it desirable that it should, filter through an agricultural soil)--the interval between two pipes will be called upon to pass two-thirds of a tablespoonful of water per minute, and no more. Inch pipes, lying at a small inclination, and running only half-full, will discharge more than double this quantity of water in forty-eight hours."

Tiles may be made of any desired form of section,--the usual forms are the "horse-shoe," the "sole," the "double-sole," and the "round." The latter may be used with collars, and they constitute the "pipes and collars," frequently referred to in English books on drainage.

Fig. 13 - HORSE-SHOE TILE.

_Horse-shoe tiles_, Fig. 13, are condemned by all modern engineers. Mr. Gisborne disposes of them by an argument of some length, the quotation of which in these pages is probably advisable, because they form so much better conduits than stones, and to that extent have been so successfully employed, that they are still largely used in this country by "amateurs."

"We shall shock some and surprise many of our readers, when we
state confidently that, in average soils, and, still more, in
those which are inclined to be tender, horse shoe tiles form the
weakest and most failing conduit which has ever been used for a
deep drain. It is so, however; and a little thought, even if we
had no experience, will tell us that it must be so. A doggrel
song, quite destitute of humor, informs us that tiles of this sort
were used in 1760 at Grandesburg Hall, in Suffolk, by Mr. Charles
Lawrence, the owner of the estate. The earliest of which we had
experience were of large area and of weak form. Constant failures
resulted from their use, and the cause was investigated; many of
the tiles were found to be choked up with clay, and many to be
broken longitudinally through the crown. For the first evil, two
remedies were adopted; a sole of slate, of wood, or of its own
material, was sometimes placed under the tile, but the more usual
practice was to form them with club-feet. To meet the case of
longitudinal fracture, the tiles were reduced in size, and very
much thickened in proportion to their area. The first of these
remedies was founded on an entirely mistaken, and the second on no
conception at all of the cause of the evil to which they were
respectively applied. The idea was, that this tile, standing on
narrow feet, and pressed by the weight of the refilled soil, sank
into the floor of the drain; whereas, in fact, the floor of the
drain rose into the tile. Any one at all conversant with
collieries is aware that when a _strait_ work (which is a small
subterranean tunnel six feet high and four feet wide or
thereabouts) is driven in coal, the rising of the floor is a more
usual and far more inconvenient occurrence than the falling of the
roof: the weight of the two sides squeezes up the floor. We have
seen it formed into a very decided arch without fracture. Exactly
a similar operation takes place in the drain. No one had till
recently dreamed of forming a tile drain, the bottom of which a
man was not to approach personally within twenty inches or two
feet. To no one had it then occurred that width at the bottom of
the drain was a great evil. For the convenience of the operator
the drain was formed with nearly perpendicular sides, of a width
in which he could stand and work conveniently, shovel the bottom
level with his ordinary spade, and lay the tiles by his hand; the
result was a drain with nearly perpendicular sides, and a wide
bottom. No sort of clay, particularly when softened by water
standing on it or running over it, could fail to rise under such
circumstances; and the deeper the drain the greater the pressure
and the more certain the rising. A horse-shoe tile, which may be a
tolerable secure conduit in a drain of two feet, in one of four
feet becomes an almost certain failure. As to the longitudinal
fracture--not only is the tile subject to be broken by one of those
slips which are so troublesome in deep draining, and to which the
lightly-filled material, even when the drain is completed, offers
an imperfect resistance, but the constant pressure together of the
sides, even when it does not produce a fracture of the soil,
catches hold of the feet of the tile, and breaks it through the
crown. Consider the case of a drain formed in clay when dry, the
conduit a horse-shoe tile. When the clay expands with moisture, it
necessarily presses on the tile and breaks it through the crown,
its weakest part.(9) When the Regent's Park was first drained,
large conduits were in fashion, and they were made circular by
placing one horse-shoe tile upon another. It would be difficult to
invent a weaker conduit. On re-drainage, innumerable instances
were found in which the upper tile was broken through the crown,
and had dropped into the lower. Next came the D form, tile and
sole in one, and much reduced in size--a great advance; and when
some skillful operator had laid this tile bottom upwards we were
evidently on the eve of pipes. For the D tile a round pipe moulded
with a flat-bottomed solid sole is now generally substituted, and
is an improvement; but is not equal to pipes and collars, nor
generally cheaper than they are."

Fig. 14 - SOLE TILE.

One chief objection to the _Sole-tiles_ is, that, in the drying which they undergo, preparatory to the burning, the upper side is contracted, by the more rapid drying, and they often require to be trimmed off with a hatchet before they will form even tolerable joints; another is, that they cannot be laid with collars, which form a joint so perfect and so secure, that their use, in the smaller drains, should be considered indispensable.

Fig. 15 - DOUBLE-SOLE TILE.

The _double-sole tiles_, which can be laid either side up give a much better joint, but they are so heavy as to make the cost of transporation considerably greater. They are also open to the grave objection that they cannot be fitted with collars.

Experience, in both public and private works in this country, and the cumulative testimony of English and French engineers, have demonstrated that the only tile which it is economical to use, is the _best_ that can be found, and that the best,--much the best--thus far invented, is the "pipe, or round tile, and collar,"--and these are unhesitatingly recommended for use in all cases. Round tiles of small sizes should not be laid without collars, as the ability to use these constitutes their chief advantage; holding them perfectly in place, preventing the rattling in of loose dirt in laying, and giving twice the space for the entrance of water at the joints. A chief advantage of the larger sizes is, that they may be laid on any side and thus made to fit closely. The usual sizes of these tiles are 1-1/4 inches, 2-1/4 inches, and 3-1/2 inches in interior diameter. Sections of the 2-1/4 inch make collars for the 1-1/4 inch, and sections of the 3-1/2 inch make collars for the 2-1/4 inch. The 3-1/2 inch size does not need collars, as it is easily secured in place, and is only used where the flow of water would be sufficient to wash out the slight quantity of foreign matters that might enter at the joints.

Fig. 16 - ROUND TILE AND COLLAR, AND THE SAME AS LAID.

*The size of tile* to be used is a question of consequence. In England, 1-inch pipes are frequently used, but 1-1/4 inch(10) are recommended for the smallest drains. Beyond this limit, the proper size to select is, _the smallest that can convey the water which will ordinarily reach it after a heavy rain_. The smaller the pipe, the more concentrated the flow, and, consequently, the more thoroughly obstructions will be removed, and the occasional flushing of the pipe, when it is taxed, for a few hours, to its utmost capacity, will insure a thorough cleansing. No inconvenience can result from the fact that, on rare occasions, the drain is unable, for a short time, to discharge all the water that reaches it, and if collars are used, or if the clay be well packed about the pipes, there need be no fear of the tile being displaced by the pressure. An idea of the drying capacity of a 1-1/4-inch tile may be gained from observing its _wetting_ capacity, by connecting a pipe of this size with a sufficient body of water, at its surface, and discharging, over a level dry field, all the water which it will carry. A 1-1/4-inch pipe will remove all the water which would fall on an acre of land in a very heavy rain, in 24 hours,--much less time than the water would occupy in getting to the tile, in any soil which required draining; and tiles of this size are ample for the draining of two acres. In like manner, 2-1/2-inch tile will suffice for eight, and 3-1/2-inch tile for twenty acres. The foregoing estimates are, of course, made on the supposition that only the water which falls on the land, (storm water,) is to be removed. For main drains, when greater capacity is required, two tiles may be laid, (side by side,) or in such cases the larger sizes of sole tiles may be used, being somewhat cheaper. Where the drains are laid 40 feet apart, about 1,000 tiles per acre will be required, and, in estimating the quantity of tiles of the different sizes to be purchased, reference should be had to the following figures; the first 2,000 feet of drains require a collecting drain of 2-1/4-inch tile, which will take the water from 7,000 feet; and for the outlet of from 7,000 to 20,000 feet 3-1/2-inch tile may be used. Collars, being more subject to breakage, should be ordered in somewhat larger quantities.

Of course, such guessing at what is required, which is especially uncertain if the surface of the ground is so irregular as to require much deviation from regular parallel lines, is obviated by the careful preparation of a plan of the work, which enables us to measure, beforehand, the length of drain requiring the different sizes of conduit, and, as tiles are usually made one or two inches more than a foot long, a thousand of them will lay a thousand feet,--leaving a sufficient allowance for breakage, and for such slight deviations of the lines as may be necessary to pass around those stones which are too large to remove. In very stony ground, the length of lines is often materially increased, but in such ground, there is usually rock enough or such accumulations of boulders in some parts, to reduce the length of drain which it is possible to lay, at least as much as the deviations will increase it.

It is always best to make a contract for tile considerably in advance. The prices which are given in the advertisements of the makers, are those at which a single thousand,--or even a few hundred,--can be purchased, and very considerable reductions of price may be secured on large orders. Especially is this the case if the land is so situated that the tile may be purchased at either one of two tile works,--for the prices of all are extravagantly high, and manufacturers will submit to large discounts rather than lose an important order.

It is especially recommended, in making the contract, to stipulate that every tile shall be hard-burned, and that those which will not give a _clear ring_ when struck with a metallic instrument, shall be rejected, and the cost of their transportation borne by the maker. The tiles used in the Central Park drainage were all tested with the aid of a bit of steel which had, at one end, a cutting edge. With this instrument each tile was "sounded," and its hardness was tested by scraping the square edge of the bore. If it did not "ring" when struck, or if the edge was easily cut, it was rejected. From the first cargo there were many thrown out, but as soon as the maker saw that they were really inspected, he sent tile of good quality only. Care should also be taken that no _over-burned_ tile,--such as have been melted and warped, or very much contracted in size by too great heat,--be smuggled into the count.

A little practice will enable an ordinary workman to throw out those which are imperfect, and, as a single tile which is so underdone that it will not last, or which, from over-burning, has too small an orifice, may destroy a long drain, or a whole system of drains, the inspection should be thorough.

The collars should be examined with equal care. Concerning the use of these, Gisborne says:

"To one advantage which is derived from the use of collars we have not yet adverted--the increased facility with which free water existing in the soil can find entrance into the conduit. The collar for a 1-1/2-inch pipe has a circumference of three inches. The whole space between the collar and the pipe on each side of the collar is open, and affords no resistance to the entrance of water; while at the same time the superincumbent arch of the collar protects the junction of two pipes from the intrusion of particles of soil. We confess to some original misgivings that a pipe resting only on an inch at each end, and lying hollow, might prove weak and liable to fracture by weight pressing on it from above; but the fear was illusory. Small particles of soil trickle down the sides of every drain, and the first flow of water will deposit them in the vacant space between the two collars. The bottom, if at all soft, will also swell up into any vacancy. Practically, if you reopen a drain well laid with pipes and collars, you will find them reposing in a beautiful nidus, which, when they are carefully removed, looks exactly as if it had been moulded for them."

The cost of collars should not be considered an objection to their use; because, without collars it would not be safe, (as it is difficult to make the orifices of two pieces come exactly opposite to each other,) to use less than 2-inch tiles, while, with collars, 1-1/4-inch are sufficient for the same use, and, including the cost of collars, are hardly more expensive.

It is usual, in all works on agricultural drainage, to insert tables and formulae for the guidance of those who are to determine the size of tile required to discharge the water of a certain area. The practice is not adopted here, for the reason that all such tables are without practical value. The smoothness and uniformity of the bore; the rate of fall; the depth of the drain, and consequent "head," or pressure, of the water; the different effects of different soils in retarding the flow of the water to the drain; the different degrees to which angles in the line of tile affect the flow; the degree of acceleration of the flow which is caused by greater or less additions to the stream at the junction of branch drains; and other considerations, arising at every step of the calculation, render it impossible to apply delicate mathematical rules to work which is, at best, rude and unmathematical in the extreme. In sewerage, and the water supply of towns, such tables are useful,--though, even in the most perfect of these operations, engineers always make large allowances for circumstances whose influence cannot be exactly measured,--but in land drainage, the ordinary rules of hydraulics have to be considered in so many different bearings, that the computations of the books are not at all reliable. For instance, Messrs. Shedd & Edson, of Boston, have prepared a series of tables, based on Smeaton's experiments, for the different sizes of tile, laid at different inclinations, in which they state that 1-1/2-inch tile, laid with a fall of one foot in a length of one hundred feet, will discharge 12,054.81 gallons of water in 24 hours. This is equal to a rain-fall of over 350 inches per year on an acre of land. As the average annual rain-fall in the United States is about 40 inches, at least one-half of which is removed by evaporation, it would follow, from this table, that a 1-1/2-inch pipe, with the above named fall, would serve for the drainage of about 17 acres. But the calculation is again disturbed by the fact that the rain-fall is not evenly distributed over all the days of the year,--as much as six inches having been known to fall in a single 24 hours, (amounting to about 150,000 gallons per acre,) and the removal of this water in a single day would require a tile nearly five inches in diameter, laid at the given fall, or a 3-inch tile laid at a fall of more than 7-1/2 feet in 100 feet. But, again, so much water could not reach a drain four feet from the surface, in so short a time, and the time required would depend very much on the character of the soil. Obviously, then, these tables are worthless for our purpose. Experience has fully shown that the sizes which are recommended below are ample for practical purposes, and probably the areas to be drained by the given sizes might be greatly increased, especially with reference to such soils as do not allow water to percolate very freely through them.

In connection with this subject, attention is called to the following extract from the Author's Report on the Drainage, which accompanies the "Third Annual Report of the Board of Commissioners of the Central Park:"

"In order to test the efficiency of the system of drainage employed on the Park, I have caused daily observations to be taken of the amount of water discharged from the principal drain of 'the Green,' and have compared it with the amount of rain-fall. A portion of the record of those observations is herewith presented.

"In the column headed 'Rain-Fall,' the amount of water falling on one acre during the entire storm, is given in gallons. This is computed from the record of a rain-gauge kept on the Park.

"Under the head of 'Discharge,' the number of gallons of water drained from one acre during 24 hours is given. This is computed from observations taken, once a day or oftener, and supposes the discharge during the entire day to be the same as at the time of taking the observations. It is, consequently, but approximately correct:

Date. Hour. Rain-fall. Discharge. Remarks.
July 13. 10 a.m. 49,916 184 galls. Ground dry.
galls. No rain
since 3d
inst.; 2
inches rain
fell between
5.15 and
5.45 p.m.
and 1-5th of
an inch
between 5.45
and 7.15.
July 14. 6-1/2 " 4,968 "
July 15. 6-1/2 " 1,325 "
July 16. 8 " 1,104 "
July 16. 6 p.m. 33,398 " 7,764 " Ground
saturated at
a depth of 2
feet when
this rain
commenced.
July 17. 4,319 "
July 18. 9 a.m. 2,208 "
July 19. 7 " 1,325 "
July 20. 6-1/2 " 993 "
July 21. 11 " 662 "
July 22. 6-1/2 " 560 "
July 23. 10 " 1,698 " 515 " This slight
rain only
affected the
ratio of
decrease.
July 24. 7 " 442 "
Nothing
worthy of
note until
Aug. 3.
Aug. 3. 6-1/2 " 8,490 " 191 " Rain from 3
p.m. to 3.30
p.m.
Aug. 4. 6-1/2 " 13,018 " 184 " " 4.45
p.m. to 12
m.n.
Aug. 5. 6-1/2 " 45,288 " 368 " " 12 m.
to 6 p.m.
Aug. 5. 6 p.m. 8,280 "
Aug. 6. 9 a.m. 3,954 "
Aug. 7. 9 " 2,208 "
Aug. 8. 6-1/2 " 828 "
Aug. 9. 6-1/2 " 662 "
Aug. 12. 6-1/2 " 368 " Rain 12 m.
Aug. 12 to 7
a.m. Aug.
13.
Aug. 13. 7 " 19,244 " 1,104 "
Aug. 14. 9 " 736 "
Aug. 24. 9 " 1,132 " 191 " " 3 a.m.
to 4.15 a.m.
Aug. 25. 9 " 5,547 " 9,936 " " 3.30
p.m. 24th,
to 7 a.m.
25th.
Aug. 25. 7 p.m. 566 " 7,740 " " 7 a.m.
to 12 m.
Aug. 26. 6-1/2 a.m. 3,974 "
Aug. 26. 6 p.m. 2,208 "
Aug. 27. 6-1/2 a.m. 566 " 1,529 " " 4 p.m.
to 6 p.m.
Aug. 28. 7 " 993 "
Sep. 11. 7 " 566 " 165 " " 12 m.n.
(10th) to 7
a.m. (11th.)
Sep. 12. 9 " 5,094 " 147 " " 12 m.
(11th) to 7
a.m. (12th.)
Sep. 13. 9 " 566 " 132 " " 4 p.m.
to 6 p.m.
Sep. 16. 9 " 15,848 " 110 " " 12 m. to
12 m.n.
Sep. 17. 7 " 27,552 " 1,104 " Rain
continued
until 12 m.
Sep. 17. 5 p.m. 6,624 "
Sep. 18. 8 a.m. 566 " 4,968 "
Sep. 19. 6-1/2 " 2,208 "
Sep. 19. 4 p.m. 1,805 "
Sep. 20. 9 a.m. 566 " 1,324 " Rain f'm 12
m. (19th) to
7 a.m.
(20th.)
Sep. 21. 9 " 5,094 " 945 " " 3.20
p.m. (20th)
to 6 a.m.
(21st.)
Sep. 22. 9 " 10,185 " 1,656 " " 12 m.
(21st) to 7
a.m. (22d.)
Sep. 23. 9 " 40,756 " 7,948 " Rain
continued
until 7 a.m.
(23d.)
Sep. 24. 9 " 4,968 "
Sep. 25. 9 " 566 " 2,984 "
Sep. 26. 9 " 2,484 "
Oct. 1. 9 " 828 " There was
not enough
rain during
this period
to
materially
affect the
flow of
water.
Nov. 18. 9 " 83 "
Nov. 19. 9 " 1,132 " 184 " Rain 4.50
p.m. (18th)
to 8 a.m.
(19th.)
Nov. 20. 9 " 119 "
Nov. 22. 9 " 29,336 " 6,624 " Rain all of
the previous
night.
Nov. 22. 2 p.m. 6,624 "
Nov. 23. 9 a.m. 4,968 "
Nov. 24. 9 " 1,711 "
Nov. 24. 2 p.m. 1,417 "
Dec. 17. 9 a.m. 552 "
Dec. 18. 9 " 4,968 " Rain during
the previous
night.
Dec. 30. 10 " 581 "

"The tract drained by this system, though very swampy, before being drained, is now dry enough to walk upon, almost immediately after a storm, except when underlaid by a stratum of frozen ground."

The area drained by the main at which these gaugings were made, is about ten acres, and, in deference to the prevailing mania for large conduits, it had been laid with 6-inch sole-tile. The greatest recorded discharge in 24 hours was (August 25th,) less than 100,000 gallons from the ten acres,--an amount of water which did not half fill the tile, but which, according to the tables referred to, would have entirely filled it.

In view of all the information that can be gathered on the subject, the following directions are given as perfectly reliable for drains four feet or more in depth, laid on a well regulated fall of even three inches in a hundred feet:

For 2 acres 1-1/4 inch pipes (with collars.)

For 8 acres 2-1/4 inch pipes (with collars.)

For 20 acres 3-1/2 inch pipes

For 40 acres 2 3-1/2 inch pipes or one 5-inch sole-tile.

For 50 acres 6 inch pipes sole-tile.

For 100 acres 8 inch pipes or two 6-inch sole-tiles.

It is not pretended that these drains will immediately remove all the water of the heaviest storms, but they will always remove it fast enough for all practical purposes, and, if the pipes are securely laid, the drains will only be benefited by the occasional cleansing they will receive when running "more than full." In illustration of this statement, the following is quoted from a paper communicated by Mr. Parkes to the Royal Agricultural Society of England in 1843:

"Mr. Thomas Hammond, of Penshurst, (Kent,) now uses no other size for the parallel drains than the inch tile in the table, (No. 5,) having commenced with No. 4,(11) and it may be here stated, that the opinion of all the farmers who have used them in the Weald, is that a bore of an inch area is abundantly large. A piece of 9 acres, now sown with wheat, was observed by the writer, 36 hours after the termination of a rain which fell heavily and incessantly during 12 hours on the 7th of November. This field was drained in March, 1842, to the depth of 30 to 36 inches, at a distance of 24 feet asunder, the length of each drain being 235 yards.

"Each, drain emptied itself through a fence bank into a running stream in a road below it; the discharge therefore was distinctly observable. Two or three of the pipes had now ceased running; and, with the exception of one which tapped a small spring and gave a stream about the size of a tobacco pipe, the run from the others did not exceed the size of a wheat straw. The greatest flow had been observed by Mr. Hammond at no time to exceed half the bore of the pipes. The fall in this field is very great, and the drains are laid in the direction of the fall, which has always been the practice in this district. The issuing water was transparently clear; and Mr. Hammond states that he has never observed cloudiness, except for a short time after very heavy flushes of rain, when the drains are quickly cleared of all sediment, in consequence of the velocity and force of the water passing through so small a channel. Infiltration through the soil and into the pipes, must, in this case, be considered to have been perfect; and their observed action is the more determinate and valuable as regards time and effect, as the land was saturated with moisture previous to this particular fall of rain, and the pipes had ceased to run when it commenced. This piece had, previous to its drainage, necessarily been cultivated in narrow stretches, with an open water furrow between them; but it was now laid quite plain, by which one-eighth of the continuation of acreage has been saved. Not, however, being confident as to the soil having already become so porous as to dispense entirely with surface drains, Mr. Hammond had drawn two long water furrows diagonally across the field. On examining these, it appeared that very little water had flowed along any part of them during these 12 hours of rain,--no water had escaped at their outfall; the entire body of rain had permeated the mass of the bed, and passed off through the inch pipes; no water perceptible on the surface, which used to carry it throughout. The subsoil is a brick clay, but it appears to crack very rapidly by shrinkage consequent to drainage."

*Obstructions.*--The danger that drains will become obstructed, if not properly laid out and properly made, is very great, and the cost of removing the obstructions, (often requiring whole lines to be taken up, washed, and relaid with the extra care that is required in working in old and soft lines,) is often greater than the original cost of the improvement. Consequently, the possibility of tile drains becoming stopped up should be fully considered at the outset, and every precaution should be taken to prevent so disastrous a result.

The principal causes of obstruction are _silt, vermin_, and _roots_.

_Silt_ is earth which is washed into the tile with the water of the soil, and which, though it may be carried along in suspension in the water, when the fall is good, will be deposited in the eddies and slack-water, which occur whenever there is a break in the fall, or a defect in the laying of the tile.

_Whenever it is possible to avoid it, no drain should have a decreasing rate of fall as it approaches its outlet._

If the first hundred feet from the upper end of the drain has a fall of three inches, the next hundred feet should not have less than three inches, lest the diminished velocity cause silt, which required the speed which that fall gives for its removal, to be deposited and to choke the tile. This defect of grade is shown in Fig. 17. If the second hundred feet has an inclination of _more_ than three inches, (Fig. 18,) the removal of silt will be even better secured than if the fall continued at the original rate. Some silt will enter newly made drains, in spite of our utmost care, but the amount should be very slight, and if it is evenly deposited throughout the whole length of the drain, (as it sometimes is when the rate of fall is very low,) it will do no especial harm; but it becomes dangerous when it is accumulated within a short distance, by a decreasing fall, or by a single badly laid tile, or imperfect joint, which, by arresting the flow, may cause as much mischief as a defective grade.

Owing to the general conformation of the ground, it is sometimes absolutely necessary to adopt such a grade as is shown in Fig. 19,--even to the extent of bringing the drain down a rapid slope, and continuing it with the least possible fall through level ground. When such changes must be made, they should be effected by angles, and not by curves. In _increasing_ the fall, curves in the grade are always advisable, in _decreasing_ it they are always objectionable, except when the decreased fall is still considerable,--say, at least 2 feet in 100 feet. The reason for making an absolute angle at the point of depression is, that it enables us to catch the silt at that point in a silt basin, from which it may be removed as occasion requires.

Fig. 19 - THREE PROFILES OF DRAINS, WITH DIFFERENT INCLINATIONS.

_A Silt Basin_ is a chamber, below the grade of the drain, into which the water flows, becomes comparatively quiet, and deposits its silt, instead of carrying it into the tile beyond. It may be large or small, in proportion to the amount of drain above, which it has to accommodate. For a few hundred feet of the smallest tile, it may be only a 6-inch tile placed on end and sunk so as to receive and discharge the water at its top. For a large main, it may be a brick reservoir with a capacity of 2 or 3 cubic feet. The position of a silt basin is shown in Fig. 19.

The quantity of silt which enters the drain depends very much on the soil. Compact clays yield very little, and wet, running sands, (quicksands,) a great deal. In a soil of the latter sort, or one having a layer of running sand at the level of the drain, the ditch should be excavated a little below the grade of the drain, and then filled to that level with a retentive clay, and rammed hard. In all cases when the tile is well laid, (especially if collars are used,) and a stiff earth is well packed around the tile, silt will not enter the drain to an injurious extent, after a few months' operation shall have removed the loose particles about the joints, and especially after a few very heavy rains, which, if the tiles are small, will sometimes wash them perfectly clean, although they may have been half filled with dirt.

_Vermin_,--field mice, moles, etc.,--sometimes make their nests in the tile and thus choke them, or, dying in them, stop them up with their carcases. Their entrance should be prevented by placing a coarse wire cloth or grating in front of the outlets, which afford the only openings for their entrance.

_Roots._--The roots of many water-loving trees,--especially willows,--will often force their entrance into the joints of the tile and fill the whole bore with masses of fibre which entirely prevent the flow of water. Collars make it more difficult for them to enter, but even these are not a sure preventive. Gisborne says:

"My own experience as to roots, in connection with deep pipe draining, is as follows: I have never known roots to obstruct a pipe through which there was not a perennial stream. The flow of water in summer and early autumn appears to furnish the attraction. I have never discovered that the roots of any esculent vegetable have obstructed a pipe. The trees which, by my own personal observation, I have found to be most dangerous, have been red willow, black Italian poplar, alder, ash, and broad-leaved elm. I have many alders in close contiguity with important drains, and, though I have never convicted one, I cannot doubt that they are dangerous. Oak, and black and white thorns, I have not detected, nor do I suspect them. The guilty trees have in every instance been young and free growing; I have never convicted an adult. These remarks apply solely to my own observation, and may of course be much extended by that of other agriculturists. I know an instance in which a perennial spring of very pure and (I believe) soft water is conveyed in socket pipes to a paper mill. Every junction of two pipes is carefully fortified with cement. The only object of cover being protection from superficial injury and from frost, the pipes are laid not far below the sod. Year by year these pipes are stopped by roots. Trees are very capricious in this matter. I was told by the late Sir R. Peel that he sacrificed two young elm trees in the park at Drayton Manor to a drain which had been repeatedly stopped by roots. The stoppage was nevertheless repeated, and was then traced to an elm tree far more distant than those which had been sacrificed. Early in the autumn of 1850 I completed the drainage of the upper part of a boggy valley, lying, with ramifications, at the foot of marly banks. The main drains converge to a common outlet, to which are brought one 3-inch pipe and three of 4 inches each. They lie side by side, and water flows perennially through each of them. Near to this outlet did grow a red willow. In February, 1852, I found the water breaking out to the surface of the ground about 10 yards above the outlet, and was at no loss for the cause, as the roots of the red willow showed themselves at the orifice of the 3-inch and of two of the 4-inch pipes. On examination I found that a root had entered a joint between two 3-inch pipes, and had traveled 5 yards to the mouth of the drain, and 9 yards up the stream, forming a continuous length of 14 yards. The root which first entered had attained about the size of a lady's little finger; and its ramifications consisted of very fine and almost silky fibres, and would have cut up into half a dozen comfortable boas. The drain was completely stopped. The pipes were not in any degree displaced. Roots from the same willow had passed over the 3-inch pipes, and had entered and entirely stopped the first 4-inch drain, and had partially stopped the second. At a distance of about 50 yards a black Italian poplar, which stood on a bank over a 4-inch drain, had completely stopped it with a bunch of roots. The whole of this had been the work of less than 18 months, including the depth of two winters. A 3-inch branch of the same system runs through a little group of black poplars. This drain conveys a full stream in plashes of wet, and some water generally through the winter months, but has not a perennial flow. I have perceived no indication that roots have interfered with this drain. I draw no general conclusions from these few facts, but they may assist those who have more extensive experience in drawing some, which may be of use to drainers."

Having considered some of the principles on which our work should be based, let us now return to the map of the field, and apply those principles in planning the work to be done to make it dry.

*The Outlet* should evidently be placed at the present point of exit of the brook which runs from the springs, collects the water of the open ditches, and spreads over the flat in the southwest corner of the tract, converting it into a swamp. Suppose that, by going some distance into the next field, we can secure an outlet of 3 feet and 9 inches (3.75) below the level of the swamp, and that we decide to allow 3 inches drop between the bottom of the tile at that point, and the reduced level of the brook to secure the drain against the accumulation of sand, which might result from back water in time of heavy rain. This fixes the depth of drain at the outlet at 3-1/2 (3.50) feet.

At that side of the swamp which lies nearest to the main depression of the up-land, (See Fig. 21,) is the proper place at which to collect the water from so much of the field as is now drained by the main brook, and at that point it will be well to place a _silt basin_ or well, built up to the surface, which may, at any time, be uncovered for an observation of the working of the drains. The land between this point and the outlet is absolutely level, requiring the necessary fall in the drain which connects the two, to be gained by raising the upper end of it. As the distance is nearly 200 feet, and as it is advisable to give a fall at least five-tenths of a foot per hundred feet to so important an outlet as this, the drain at the silt basin may be fixed at only 2-1/2 feet. The basin being at the foot of a considerable rise in the ground, it will be easy, within a short distance above, to carry the drains which come to it to a depth of 4 feet,--were this not the case, the fall between the basin and the outlet would have to be very much reduced.

*Main Drains.*--The valley through which the brook now runs is about 80 feet wide, with a decided rise in the land at each side. If one main drain were laid in the center of it, all of the laterals coming to the main would first run down a steep hillside, and then across a stretch of more level land, requiring the grade of each lateral to be broken at the foot of the hill, and provided with a silt basin to collect matters which might be deposited when the fall becomes less rapid. Consequently, it is best to provide two mains, or collecting drains, (_A_ and _C_,) one lying at the foot of each hill, when they will receive the laterals at their greatest fall; but, as these are too far apart to completely drain the valley between them, and are located on land higher than the center of the valley, a drain, (_B_,) should be run up, midway between them.

The collecting drain, _A_, will receive the laterals from the hill to the west of it, as far up as the 10-foot contour line, and, above that point,--running up a branch of the valley,--it will receive laterals from both sides. The drain, _B_, may be continued above the dividing point of the valley, and will act as one of the series of laterals. The drain, _C_, will receive the laterals and sub-mains from the rising ground to the east of it, and from both sides of the minor valley which extends in that direction.

Most of the valley which runs up from the easterly side of the swamp must be drained independently by the drain _E_, which might be carried to the silt basin, did not its continuation directly to the outlet offer a shorter course for the removal of its water. This drain will receive laterals from the hill bordering the southeasterly side of the swamp, and, higher up, from both sides of the valley in which it runs.

In laying out these main drains, more attention should be given to placing them where they will best receive the water of the laterals, and on lines which offer a good and tolerably uniform descent, than to their use for the immediate drainage of the land through which they pass. Afterward, in laying out the laterals, the use of these lines as local drains should, of course, be duly considered.

*The Lateral Drains* should next receive attention, and in their location and arrangement the following rules should be observed:

1st. They should run down the steepest descent of the land.

2d. They should be placed at intervals proportionate to their depth;--if 4 feet deep, at 40 feet intervals; if 3 feet deep, at 20 feet intervals.

Fig. 20 - MAP WITH DRAINS AND CONTOUR LINES.

3d. 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 nearly 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 economy 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 intervals than are required,--for instance, at _C 7 a_ 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 _C 14_, 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 indispensable, except where the laterals can run independently across the entire field, and discharge beyond it. The longer the laterals can be made, and the more angles 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 be 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 _F_ and _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 3-1/2 (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 field, the next thing to be attended to is

*The Ordering of the Tile.*--The main line from the outlet up to the silt-basin, should be of 3-1/2-inch tiles, of which about 190 feet will be required. The main drain _A_ should be laid with 2-1/4-inch 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 1-1/4-inch tile. The length of this drain, from the silt-basin to that point is 575 feet. The main drain _C_ will require 2-1/4 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 2-1/4-inch tiles from the outlet to the point marked _o_, 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 1-1/4-inch pipe.(12)

The length of the main drains above the points indicated, and of all the laterals, amounts to about 12,250 feet. These all require 1-1/4-inch tiles.

Allowing about five per cent. for breakage, the order in round numbers, will be as follows:(13)

3-1/2-inch round tiles 200 feet.

2-1/4-inch round tiles 1,500 feet.

1-1/4-inch round tiles 13,000 feet.

3-1/2-inch round tiles 1,600

2-1/4-inch round tiles 13,250

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 _C1_, _C6_, _C9_, _C10_, and _C17_, 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 horizontal 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.(14)