DRAINING. 



DRAINING. 



630 



stratum likely to feed any surface springs or watercourses, as Croydon 

 or Ipswich, for instance, very serious evil would be produced by 

 neglecting to provide as energetically for the removal of rain or of 

 subterranean waters, as by neglecting to remove the house refuse. 

 The impermeable stoneware drains, which it is now the fashion to 

 recommend indiscriminately, are, in fact, very often a source of great 

 mischief, unless they are accompanied by a series of permeable subsoil 

 drains. The latter must be made of sufficient dimensions to carry off 

 at once the maximum quantity of rain which may run oft' from the 

 drainage area, and those dimensions must therefore be materially affected 

 by the nature of the surface of the said area, or, in other words, by the 

 consideration as to whether it be or be not built upon, or whether it 

 be paved or merely ordinary ground ; the relief of the surface will 

 also materially influence the rapidity with which the rain-now of a 

 town will find its way into the drains. Generally speaking it is found, 

 moreover, that the subsoil waters which find their way into town 

 drains are exposed to such extraordinary chemical re-actions, that they 

 are as little fitted to be poured into the superficial watercourses as even 

 the waters of sewers. 



DRAINING. As a certain quantity of moisture is essential to 

 vegetation, so an excess of it is highly detrimental. In the removal of 

 this excess consists the art of draining. The same, or nearly the same 

 truth, may perhaps be better expressed thus : As water stagnant in 

 the soil is prejudicial to the growth of all our cultivated plants, fertility 

 is greatly promoted by the art of draining, which induces its circulation 

 through the soil. 



Water may render land unproductive by covering it entirely or 

 partially, forming lakes or bogs ; or there may be an excess of moisture 

 diffused through the soil and stagnating in it, by which the fibres of 

 the roots of all plants which are not aquatic are injured, if not 

 destroyed. 



From these different causes of infertility arise three different branches 

 of the art of draining, which require to be separately noticed. 



1. To drain land which is flooded or rendered marshy by water 

 coming over it from a higher level, and having no adequate outlet 

 below. 



2. To drain land where springs rise to the surface, and where there 

 are no natural channels for the water to run off. 



3. To drain land which is wet from its impervious nature. 



The first branch includes all those extensive operations where large 

 tracts of land are reclaimed by means of embankment*, canals, sluices, 

 and mills to raise the water ; or where deep cuts or tunnels are made 

 through hills which formed a natural dam or barrier to the water. 

 Such works are generally undertaken by associations under the sanc- 

 tion of the government, or by the government itelf ; few individuals 

 being possessed of sufficient capital, or having the power to oblige all 

 whose interests are affected by the draining of the land, to give their 

 consent and afford assistance. In the British dominions there is no 

 difficulty in obtaining the sanction of the legislature to any under- 

 taking which appears likely to be of public benefit. In every session 

 of parliament Acts are passed giving certain powers and privileges to 

 companies or individuals, in order to enable them to put into execution 

 extensive plans of draining. That extensive draining in the counties 

 of Northampton, Huntingdon, Cambridge, Lincoln, Norfolk, and Suffolk, 

 which is known by the name of the BEDFORD LEVEL [GEOG. Div.], 

 was confided to the management of a chartered corporation, with 

 considerable powers, as early as the middle of the 17th century, and 

 by this means an immense extent of land has been rendered highly 

 productive, which before was nothing but one continued marsh or fen. 



In the valleys of the Jura, in the canton of Neufchatel in Switzer- 

 land, which are noted for their industry and prosperity, extensive 

 lakes and marshes have been completely laid dry, by making a tunnel 

 through the solid rock, and forming an outlet for the waters. All 

 these operations require the science and experience of civil engineers, 

 and cannot be undertaken without great means. The greater part of 

 the lowlands in the Netherlands, and especially in Holland, have been 

 reclaimed from the sea, or the rivers which flowed over them, by 

 embanking and draining, and are only kept from floods by a constant 

 attention to the works originally erected. 



Where the land is below the level of the sea at high water, it requires 

 a constant removal of the water which percolates through the banks 

 or accumulates by rains ; and this can only be effected by sluices and 

 mills, as is the case in the fens in England. The water is collected in 

 numerous ditches and canals, and led to the points where it can most 

 conveniently be discharged over the banks. The mills commonly 

 erected for this purpose are driven by steam-power, and are true 

 water-wheels, lifting by their float-boards enormous quantities at every 

 revolution from the lower to the higher level. 



In hilly countries it sometimes happens that the waters which run 

 down the slopes of the hills collect in the bottoms where there is no 

 outlet, and where the soil is impervious. In that case it may some- 

 times be laid dry by cutting a sufficient channel all round, to intercept 

 the waters as they flow down and to carry them over or through the 

 lowes part of the surrounding barrier. We shall see that this prin- 

 ciple may be applied with great advantage in many cases where the 

 watr could not be drained out of considerable hollows if it were 

 allowed to run into them. 



When there are different levels at which the water is pent up, the 



draining should always be begun at the highest; because it may happen 

 that when this is laid dry, the lower may not have a great excess of 

 water. At all events, if the water is to be raised by mechanical 

 power, there is a saving in raising it from the highest level, instead 

 of letting it run down to a lower from which it has to be raised so 

 much higher. 



The draining of laud which is rendered wet by sin-ings arising from 

 under the soil is a branch of more general application. The principles 

 on which the operations are carried on apply as well to a small field as 

 to the greatest extent of land, The object is to find the readiest chan- 

 nels by which the superfluous water may be carried off; and for this 

 purpose an accurate knowledge of the strata through which the springs 

 rise is indispensable. It would be useless labour merely to let the water 

 run into drains after it has sprung through the soil and appears at the 

 surface, as ignorant men frequently attempt to do, and thus carry it 

 off after it has already soaked the soil. But the origin of the springs 

 must, if possible, be detected; and one single drain or ditch judiciously 

 disposed may lay a great extent of land dry if it cuts off the springs 

 before they run into the soil. Abundant springs which flow con- 

 tinually generally proceed from the outbreaking of some porous 

 stratum in which the waters were confined, or through natural crevices 

 in rocks or impervious earth. A knowledge of the geology of the 

 country will greatly assist in tracing this, and the springs may be cut 

 off with greater certainty. But it is not these main springs which give 

 the greatest trouble to an experienced drainer ; it is the various land 

 springs which are sometimes branches of the former, and often original 

 and independent springs arising from sudden variations in the nature 

 of the soil and subsoil. The annexed diagram, representing-a section 

 of an uneven surface of land will explain the nature of the strata which 

 produce springs. 



Suppose A A to be a porous substance through which the water 

 filtrates readily ; and B B to be a stratum of loam or clay impervious to 

 water. The water which comes through A A will run along the surface 

 of B B towards s s, where it will spring to the surface and form a lake 

 or bog between s and s. Suppose another gravelly or pervious stratum 

 under the last, as c c c bending as here represented, and filled with 

 water running into it from a higher level ; it is evident that this 

 stratum will be saturated with water up to the dotted line E F F, which 

 is the level of the point in the lower rock, or impervious stratum D D, 

 where the water can run over it. If the stratum B B has any crevices in 

 it below the dotted line the water will rise through these to the surface 

 and form springs rising from the bottom of the lake or bog ; and if B B 

 were bored through and a pipe inserted rising up to the dotted line, as 

 co, the water would rise and stand at o. If there were no springs at 

 s 8, the space below the dotted line might still be filled with water 

 rising from the stratum c C C ; but if the boring took place at G tho 

 water would not rise, but on the contrary, if there were any on the 

 surface, it would be carried down to the porous stratum E c c and run 

 off. Thus in one situation boring will bring water, and in another it 

 will take it off. This principle being well understood will greatly 

 facilitate all draining of springs. Wherever water springs there must 

 a be pervious and an impervious stratum to cause it, and the water 

 either runs over the impervious surface or rises through the crevices 

 in it. When the line of the springs is found, as at s s, the obvious 

 remedy is to cut a channel with a sufficient declivity to take off the 

 water in a direction across this line, and sunk through the porous soil 

 at the surface into the lower impervious earth. The place for this 

 channel is where the porous soil is the shallowest above the breaking 

 out, so as to require the least depth of drain ; but the solid stratum 

 must be reached, or the draining will be imperfect. It was by attending 

 to all these circumstances that Elkington acquired his celebrity in 

 draining, and that he has been considered as the father of the system. 

 It is however of much earlier invention, and is too obvious not to have 

 struck any one who seriously considered the subject. In the practical 

 application of the principle great ingenuity and skill may be dis- 

 played, and the desired effect may be produced more or less com- 

 pletely, and at a greater or less expense. The advice of a scientific 

 and practical drainer is always well worth the cost at which it may be 

 obtained. 



When there is a great variation in the soil, and it is difficult to find 

 any main line of springs, it is best to proceed experimentally by making 

 pits a few feet deep, or by boring in various parts where water appears, 

 observing the level at which the water stands in these pits or bores, as 

 well as the nature of the soil taken out. Thus it will generally be 

 easy to ascertain whence the water arises, and how it may ba let off. 

 When there is a mound of light eoil over a more impervious stratum, 

 the springs will break out all round the edge of the mound ; a drain 

 laid round the base will take off all the water which arises from this 

 cause, and the lower part of the laud will be effectually laid dry. So, 

 likewise, where there is a hollow or depression of which the bottom is 

 clay with sand in the upper part, a dram laid along the edge of the 



