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IRRIGATION (Lat. in, and rigare, to w...
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See also:IRRIGATION (See also:Lat. in, and rigare, to See also:water or wet) , the artificial application of See also:water to See also:land in See also:order to promote vegetation; it is therefore the converse of " drainage " (q.v.), which is the artificial withdrawal of water from lands that are over-saturated . In both cases the See also:object is to promote vegetation . I . See also:General.—Where there is abundance of rainfall, and when it falls at the required See also:season, there is in general no need for See also:irrigation . But it often happens that, although there is sufficient rainfall to raise an inferior See also:crop, there is not enough to raise a more valuable one . Irrigation is an See also:art that has been practised from very See also:early times . See also:Year after year fresh discoveries are made that carry back our knowledge of the early See also:history of See also:Egypt . It is certain that, until the See also:cultivator availed himself of the natural overflow of the See also:Nile to saturate the See also:soil, Egypt must have been a See also:desert, and it is a very small step from that to baling up the water from the See also:river and pouring it over lands which the natural See also:flood has not touched . The sculptures and paintings of See also:ancient Egypt See also:bear no trace of anything approaching scientific irrigation, but they often show the See also:peasant baling up the water at least as early as 2000 B.C . By means of this See also:simple See also:plan of raising water and pouring it over the See also:fields thousands of acres are watered every year in See also:India, and the See also:system has many advantages in the eyes of the peasant . Though there is See also:great See also:waste of labour, he can apply his labour when he likes; no permission is required from a See also:government See also:official; no one has to be bribed . The simplest and earliest See also:form of water-raising machinery is the See also:pole with a bucket suspended from one end of a crossbeam and a counterpoise at the other .
In India this is known as the den/di or paecottah; in Egypt it is called the shaduf
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All along the Nile See also:banks from See also:morning to See also:night may be seen See also: In See also:Spain irrigation may be traced directly to the Moorish occupation, and almost everywhere throughout See also:Asia and See also:Africa where the Moslem penetrated is to be found some knowledge of irrigation . Reservoirs are familiar everywhere for the water-See also:supply of towns, but as the See also:volume necessary, even for a large See also:town, does Spam. not go far in irrigating land, many sites which would do admirably for the former would not contain water sufficient to be See also:worth applying to the latter purpose . In the Mediterranean provinces of Spain there are some very remark- able irrigation dams . The great See also:masonry See also:dam of See also:Alicante on the river Monegre, which See also:dates from 1579, is situated in a narrow See also:gorge, so that while 140 ft. high, it is only too ft. long at the See also:crest . The See also:reservoir is said to contain 130 million cub. ft. of water, and to serve for the irrigation of 9000 acres, but unless it refills several times a year, it is hardly possible that so much land can be watered in any one season . The See also:Elche reservoir,in the same See also:province, has a similar dam 55 ft. high . In neither See also:case is there a waste-See also:weir, the surplus water being allowed to pour over the crest of the dam . See also:South of Elche is the province of See also:Murcia, watered by the river See also:Segura, on which there is a dam 25 ft. high, said to be 800 years old, and to serve for the irrigation of 25,000 See also:act s . The See also:Lorca dam in the same neighbourhood irrigates 27,000 acres . In the jungles of See also:Ceylon are to be found remains of gigantic irrigation dams, and on the neighbouring mainland of See also:Southern India, throughout the provinces Ind/a. of See also:Madras and See also:Mysore, the See also:country is covered with irrigation reservoirs, or, as they are locally termed, tanks . These vary from See also:village ponds to lakes 14 or 15 m. long . Most of them are of old nafive construction, but they have been greatly improved and enlarged within the last See also:half See also:century . The casual traveller in southern India constantly remarks the ruins of old dams, and the impression is conveyed that at one See also:time, before See also:British See also:rule prevailed, the irrigation of the country was much more perfect than it is now . That idea, however, is mistaken . An irrigation reservoir, like a human being, has a certain See also:life . Quicker or slower, the water that fills it will wm h in See also:sand and mud, and year by year this See also:process will go on till ultimately the whole reservoir is filled up . The See also:embankment is raised, and raised again, but at last it is better to abandon it and make a new tank elsewhere, for it would never pay to dig out the silt by See also:manual labour . It may safely be said that at no time in history were there more tanks in operation than at See also:present . The ruins which are seen are the ruins of long centuries of tanks that once flourished and became silted up . But they did not all flourish at once . In the countries now being considered, the test of an irrigation See also:work is how it serves in a season of drought and See also:famine . It is evident that if there is a long cessation of See also:rain, there can be none to fill the reservoirs . In See also:September 1877 there were very few in all southern India that were not dry . But even so, they helped to shorten the famine See also:period; they stored up the rain after it had ceased to fall, and they caught up and husbanded the first drops when it began again . Irrigation effected by river-fed canals naturally depends on the regimen of the rivers . Some rivers vary much in their See also:discharge at different seasons . In some cases this variation is comparatively little . Sometimes the flood season recurs regularly at the same time of the year; sometimes it is uncertain . In some rivers the water is generally pure; in others it is highly charged with fertilizing See also:alluvium, or, it may be, with barren silt . In countries nearly rainless, such as Egypt or See also:Sind, there can be no cultivation without irrigation . Elsewhere the rainfall may be sufficient for See also:ordinary crops, but not for the more valuable kinds . In ordinary years in southern India the See also:maize and the See also:millet, which form so large a portion of the peasants' See also:food, can be raised without irrigation, but it is required for the more valuable See also:rice or See also:sugar-See also:cane . Elsewhere in India the rainfall is usually sufficient for all the cultivation of the See also:district, but about every eleven years comes a season of drought, during which See also:canal water is so See also:precious as to make it worth while to construct costly canals merely to serve as a See also:protection against famine . When a river partakes of the nature of a torrent, dwindling to a paltry stream at one season and swelling into an enormous flood at another, it is impossible to construct a system of irrigation canals without very costly See also:engineering See also:works, sluices, dams, waste-weirs, &c., so as to give the engineer entire See also:control of the water . Such may be seen on the canals of See also:Cuttack, derived from the See also:Mahanadi, a river of which the discharge does not exceed 400 cub. ft. per second in the dry season, and rises to 1,600,000 cub . It. per second in the. See also:rainy season . Very differently situated are the great canals of See also:Lombardy, See also:drawn from the See also:Ticino and See also:Adda rivers, flowing from the See also:Maggiore and See also:Como lakes . The severest drought never exhausts these reservoirs, and the heaviest rain can never convert these rivers into the resistless floods which they would be but for the moderate See also:ing See also:influence of the great lakes . The Ticino and Adda do not rise in floods more than 6 or i ft. above their ordinary level, Irrigation canals . or fall in droughts more than 4 or g ft. below it, and their water is at all seasons very See also:free from silt or mud . Irrigation cannot be practised in more favourable circumstances than these . The great lakes of Central Africa, See also:Victoria and See also:Albert See also:Nyanza, and the vast swamp See also:tract of the See also:Sudan, do for the Nile on a gigantic See also:scale what Lakes Maggiore and Como do for the rivers Ticino and Adda . But for these great reservoirs the Nile would decrease in summer to quite an insignificant stream . India possesses no great lakes from which to draw rivers and canals, but through the plains of northern India flow rivers which are fed from the glaciers of the See also:Himalaya; and the See also:Ganges, the See also:Indus, and their tributaries are thus prevented from diminishing very much in volume . The greater the See also:heat, the more rapidly melts the See also:ice, and the larger the quantity of water available for irrigation . The canal system of northern India is the most perfect the See also:world has yet seen, and contains works of See also:hydraulic engineering which can be equalled in no other country . In the deltas of southern India irrigation is only practised during the See also:monsoon season . The Godaveri . See also:Kistna and Kaveri all take their rise on the Western See also:Ghats, a region where the rainfall is never known to fail in the monsoon season . Across the See also:apex of the deltas are built great weirs (that of the Godaveri being 21 M. long), at the ends and centre of which is a system of sluices feeding a network of canals . For this monsoon irrigation there is always abundance of water, and so long as the canals and sluices are kept in repair, there is little trouble in distributing it over the fields . Similar in See also:character was the ancient irrigation of Egypt practised merely during the Nile flood—a system which still prevails in See also:part of Upper Egypt . A detailed description of it will be found below . Where irrigation is carried on throughout the whole year, even when the supply of the river is at its lowest, the See also:distribution of the water becomes a very delicate operation . It is generally considered sufficient in such cases if during any one crop one-third of the See also:area that can be com- manded is actually supplied with water . This encourages a rotation of crops and enables the precious liquid to be carried over a larger area than could be done otherwise . It becomes then the See also:duty of the engineer in See also:charge to use every effort to get its full value out of every cubic See also:foot of water . Some crops of course require water much oftener than others, and much depends on the temperature at the time of irrigation . During the See also:winter months in northern India magnificent See also:wheat crops can be produced that have been watered only twice or thrice . But to keep sugar-cane, or See also:indigo, or See also:cotton alive in summer before the monsoon sets in in India or the Nile rises in Egypt the field should be watered every ten days or fortnight, while rice requires a See also:constant supply of water passing over it . Experience in these sub-tropical countries shows the See also:absolute See also:necessity of having, for successful irrigation, also a system of thorough drainage . It was some time before this was discovered in India, and the result has been the deterioration of much See also:good land . In Egypt, See also:prior to the British occupation in 1883, no See also:attempt had been made to take the water off the land . The first impression of a great alluvial See also:plain is that it is absolutely See also:flat, with no drainage at all . Closer examination, however, shows that if the prevailing slopes are not more than a few inches in the mile, yet they do exist, and scientific irrigation requires that the canals should be taken along the crests and drains along the hollows . In the See also:diagram (fig . I) is shown to the right of the river a system of canals branching out and afterwards rejoining one another so as to allow of no means for the water that passes off the field to See also:escape into the See also:sea . Hence it must either evaporate or sink into the soil . Now nearly all rivers contain some small percentage of See also:salt, which forms a distinct ingredient in alluvial plains . The result of this drainless irrigation is an efflorescence of salt on the surface of the field . The spring level rises, so that water can be reached by digging only a few feet, and the land, soured and water-logged, relapses into barrenness . Of this description was the irrigation of See also:Lower Egypt previous to 1883 . To the See also:left of the diagram is shown (by See also:firm lines) a system of canalslaid out scientifically, and of drains (by dotted lines) flowing between them . It is the effort of the British See also:engineers in Egypt to remodel the surface of the fields to this type . Further See also:information may be found in See also:Sir C . C . See also:Scott-Moncrieff, Irrigation in Southern See also:Europe (See also:London, 1868) ; Moncrieff, " Lectures on Irrigation in Egypt," Professional Papers of the See also:Corps of Royal Engineers, vol. xix . (London, 1893) ; W . Willcocks, Egyptian Irrigation (2nd ed., London, 1899) . II . Water Meadows.—Nowhere in See also:England can it be said that irrigation is necessary to ordinary See also:agriculture, but it is occasion-ally employed in stimulating the growth of grass and meadow herbage in what are known as water-meadows . These are in some instances of very early origin . On the See also:Avon in See also:Wiltshire and the See also:Churn in See also:Gloucestershire they may be traced back to See also:Roman times . This irrigation is not practised in the drought of summer, but in the coldest and wettest months of the year, SEA trngabion, dasazbutary Cmlalr . Drainage ithes the water employed being warmer than the natural moisture of the soil and proving a valuable protection against See also:frost . Before the systematic See also:conversion of a tract into water-meadows can be safely determined on, care must be taken to have good drainage, natural or artificial, a sufficient supply of water, and water of good quality . It might indeed have been thought that thorough drainage would be unnecessary, but it must be noted that porous subsoils or efficient drains do not act merely by carrying away stagnant water which would otherwise cool the See also:earth, incrust. the surface, and retard plant growth . They, cause the soil to perform the See also:office of a See also:filter . Thus the earth and the roots of See also:grasses absorb the useful matters not only from the water that passes over it, but from that which passes through it . These fertilizing materials are found stored up in the soil ready for the use of the roots of the See also:plants . Stagnation of water is inimical to the See also:action of the roots, and does away with the advantageous processes of flowing and percolating currents . Some of the best water-meadows in England have but a thin soil resting on See also:gravel and flints, this constituting a most effectual system of natural drainage . The fall of the water supply must suffice for a fairly rapid current, say Io in. or t ft. in from too to Distribution of the water . 200 yds . If possible the water should be taken so far above the meadows as to have sufficient fall without damming up the river . If a dam be absolutely necessary, care must be taken so to build it as to secure the fields on both sides from possible inundation; and it should be constructed substantially, for the cost of repairing accidents to a weak dam is very serious . Even were the See also:objects of irrigation always identical, the conditions under which it is carried on are so variable as to preclude calculations of quantity . See also:Mere making up of necessary Quantity water in droughty seasons is one thing, protection of water. against frost is another, while the addition of soil material is a third . Amongst causes of variation in the quantity of water needed will be its quality and temperature and See also:rate of flow, the See also:climate, the season, the soil, the subsoil, the artificial drainage, the slope, the aspect and the crop . In actual practice the amount of water varies from 300 gallons per See also:acre in the See also:hour to no less than 28,000 gallons . Where water is used, as in dry and hot countries, simply as water, less is generally needed than in See also:cold, See also:damp and northerly climates, where the higher temperature and the action of the water as manure are of more See also:con-sequence . But it is necessary to be thoroughly assured of a good supply of water before laying out a water-meadow . Except in a few places where unusual dryness of soil and climate indicate the employment of water, even in small quantity, merely to avoid the consequences of drought, irrigation works are not to be commenced upon a large area, if only a part can ever be efficiently watered . The engineer must not decide upon the plan till he has gauged at different seasons the stream which has to supply the water, and has ascertained the rain-See also:collecting area available, and the rainfall of the district, as well as the proportion of storable to percolating and evaporating water . Reservoirs for storage, or for equalizing the flow, are rarely resorted to in England; but they are of absolute necessity in those countries in which it is just when there is least water that it is most wanted . It is by no means an injudicious plan before laying out a system of water-meadows, which is intended to be at all extensive, to prepare a small trial See also:plot, to aid in determining a number of questions See also:relating to the nature and quantity of the water, the porosity of the soil, &c . The quality of the water employed for any of the purposes of irrigation is of much importance . Its dissolved and its See also:sus- pended matters must both be taken into See also:account . Clear arable land . If it is to be used for warping, or in any way for adding to the solid material of the irrigated land, then the nature and amount of the suspended material are necessarily of more importance than the character of the dissolved substances, provided the latter are not positively injurious . For use on ordinary water-meadows, however, not only is very clear water often found to be perfectly efficient, but water having no more than a few grains of dissolved See also:matter per See also:gallon answers the purposes in view satisfactorily . Water from See also:moors and See also:peat-bogs or from gravel or ferruginous See also:sandstone is generally of small utility so far as plant food is concerned . River water, especially that which has received town sewage, or the drainage of highly manured land, would naturally be considered most suitable for irrigation, but excellent results are obtained also with See also:waters which are uncontaminated with manurial matters, and which contain but 8 or so grains per gallon of the usual dissolved constituents of spring water . Experienced See also:English irrigators generally commend as suitable for water-meadows those streams in which See also:fish and waterweeds abound . But the particular plants present in or near the water-supply afford further indications of quality . Water-See also:cress, sweet See also:flag, flowering See also:rush, several potamogetons, water milfoil, water See also:ranunculus, and the reedy sweet watergrass (Glyceria a.quatica) See also:rank amongst the criteria of excellence . Less favourable signs are furnished by such plants as Arundo Donax (in See also:Germany) j Cicula virosa and Typha latifolia, which are found in stagnant 'and torpid waters . Water when it has been used for irrigation generally becomes of less value for the same purpose . This occurs with clear water as well as with turbid, and obviously arises mainly from theloss of plant food which occurs when water filters through or trickles over poor soil . By passing over or through See also:rich soil the water may, however, actually be enriched, just as clear water passed through a See also:charcoal filter which has been long used becomes impure . It has been contended that irrigation water suffers no See also:change in See also:composition by use, since by evaporation of a part of the pure water the dissolved matters in the See also:remainder would be so increased as to make up for any matters removed . But it is forgotten that both tta plant and the soil enjoy See also:special See also:powers of selective absorption, which remove and See also:fix the better constituents of the water and leave the less valuable . Of the few leguminous plants which are in any degree suitable for water-meadows, See also:Lotus corniculatus See also:major, Trifolium hybridum, and T. pratense are those which generally flourish best; T. repens is less successful . Amongst grasses See also:Seed:= for the highest See also:place must be assigned to ryegrass, especially Y meadows. to the See also:Italian variety, commonly called Lolium italicum . The mixture of seeds for See also:sowing a water-meadow demands much See also:consideration, and must be modified according to See also:local circumstances of soil, aspect, climate and drainage . From the See also:peculiar use which is made of the produce of an irrigated meadow, and from the conditions to which it is subjected, it is necessary to include in our mixture of seeds some that produce an early crop, some that give an abundant growth, and some that impart sweetness and good flavour, while all the kinds sown must be capable of flourishing on irrigated soil . The following mixtures of seeds (stated in pounds per acre) have been recommended for sowing on water-meadows, Messrs See also:Sutton of See also:Reading, after considerable experience, regarding No . I. as the more suitable: 1 . II . 1 . IT . Lolium perenne 8 I2 Festuca pratensis . . 0 2 Lolium italicum 0 8 Festuca loliacea . 3 2 Poa trivialis . 6 3 Anthoxanthum odoratum o I See also:Glycerin fluitans 6 2 Phleum pratense . . 4 2 Glyceria aquatica . 4 I See also:Phalaris arundinacea 3 2 Agrostis See also:alba . . 0 I Lotus corniculatus major 3 2 Agrostis stolonifera . 6 2 Trifolium hybridum . . o I Alopecurus pratensis 0 2 Trifolium pratense . . o r Festuca elatior . . 3 2 In irrigated meadows, though in a less degree than on sewaged land, the reduction of the amount or even the actual suppression of certain See also:species of plants is occasionally well marked . Sometimes this action is exerted upon the finer grasses, but happily also upon some of the less profitable constituents of the See also:miscellaneous herbage . Thus Ranunculus bulbosus has been observed to become quite rare after a few years' watering of a meadow in which it had been most abundant, R. acris rather increasing by the same treatment; Plantago See also:media was extinguished and P. lanceolata reduced 70% . Amongst the grasses which may be spared, Aira caespitosa, Briza media and Cynosurus cristatus are generally much reduced by irrigation . Useful grasses which are increased are Lolium perenne and Alopecurus pratensis, and among those of less value Avena favescens, Dactylis glomerata and Poa pratensis . Four ways of irrigating land with water are practised in England: (I) bedwork irrigation, which is the most efficient although it is also the most costly method by which Methods. currents of water can be applied to level land; (2) catchwork irrigation, in which the same water is caught and used repeatedly; (3) subterraneous or rather upward irrigation, in which the water in the drains is sent upwards through the soil towards the surface; and (4) warping, in which the water is allowed to stand over a level field until it has deposited the mud suspended in it . There are two things to be attended to most carefully in the construction of a water-meadow on the first or second of these plans . First, no portion of them whatever should be on a dead level, but every part should belong to one or other of a See also:series of true inclined planes . The second point of See also:primary importance is the See also:size and slope of the See also:main conductor, which brings the water from the river to the meadow . The size of this depends Quality water, of water is usually preferable for grass land, thick for water . Changes in irrigated herbage . upon the quantity of water required, but whatever its size its bottom at its origin should be as See also:low as the See also:bed of the river, in order that it may carry down as much as possible of the river mud . Its course should be as straight and as near a true inclined See also:plane as possible . The stuff taken out of the conductor should be employed in making up its banks or correcting inequalities in the meadow . In bedwork irrigation, which is eminently applicable to level ground, the ground is thrown into beds or ridges . Here the con-Bedwork. ductor should be led along the highest end or See also:side of the meadow in an inclined plane; should it terminate in the meadow, its end should be made to See also:taper when there are no feeders, or to terminate in a feeder . The main drain to carry off the water from the meadow should next be formed . It should be cut in the lowest part of the ground at the lower end or side of the meadow . Its dimensions should be capable of carrying off the whole water used so quickly as to prevent the least stagnation, and discharge it into the river . The next process is the forming of the ground in-tended for a water-meadow into beds or ridges . That portion of the ground which is to be watered by one conductor should be made into beds to suit the circumstances of that conductor; that is, instead of the beds over the meadow being all reduced to one See also:common level, they should be formed to suit the different swells in the ground, and, should any of these swells be considerable, it will be necessary to give each side of them its respective conductor . The beds should run at or nearly at right angles to the See also:line of the conductor . The breadth of the beds is regulated by the nature of the soil and the supply of water . Tenacious soils and subsoils, with a small supply of water, require beds as narrow as 30 ft . Porous soils and a large supply of water may have beds of 40 ft . The length of the beds is regulated by the supply of water and the fall from the conductor to the main drain . If the beds fall only in one direction longitudinally, their crowns should be made in the See also:middle; but, should they fall laterally as well as longitudinally, as is usually the case, then the crowns should be made towards the upper sides, more or less ac-cording to the lateral slope of the ground . The crowns should rise i ft. above the adjoining furrows . The beds thus formed should slope in an inclined plane from the conductor to the main drain, that the water may flow equably over them . The beds are watered by " feeders," that is, channels gradually tapering to the lower extremities, and their crowns cut down, wherever these are placed . The depth of the feeders depends on their width, and the width on their length . A bed 200 yds. in length requires a feeder of 20 in. in width at its junction with the conductor, and it should taper gradually to the extremity, which should be i ft. in width . The taper retards the See also:motion of the water, which constantly decreases by overflow as it proceeds, whilst it continues to fill the feeder to the brim . The water overflowing from the feeders down the sides of the beds is received into small drains formed in the furrows between the beds . These small drains discharge themselves into the main drain, and are in every respect the See also:reverse of the feeders . The depth of the small drain at the junction is made about as great as that of the main drain, and it gradually lessens towards the taper to 6 in. in tenacious and to less in porous soils . The depth of the feeders is the same in relation to the conductor . For the more equal distribution of the water over the surface of the beds from the conductor and feeders, small masses, such as stones or solid portions of earth or See also:turf fastened with pins, are placed in them, in order to retard the momentum which the water may have acquired . These " stops," as they are termed, are generally placed at See also:regular intervals, or rather they should be left where any inequality of the current is observed . Heaps of stones See also:answer very well for stops in the conductor, particularly immediately below the points of junction with the feeders . The small or main drains require no stops . The descent of the water in the feeders will no doubt necessarily increase in rapidity, but the inclination of the beds and the tapering of the feeders should be so adjusted as to counteract the increasing rapidity . The distribution of the water over the whole meadow is regulated by the sluices, which should be placed at the origin of every conductor . By means of these sluices any portion of the meadow that is desired can be watered, whilst the See also:rest remains dry; and alternate watering must be adopted when there is a scarcity of water . All the sluices should be substantially built at first with stones and See also:mortar, to prevent the leakage of water; for, should water from a leak be permitted to find its way into the meadow, that portion of it will stagnate and produce coarse grasses . In a well-formed water-meadow it is as necessary to keep it perfectly dry at one time as it is to place it under water at another . A small sluice placed in the side of the conductor opposite to the meadow, and at the upper end of it, will drain away the leakage that may have escaped from the See also:head sluice . To obtain a See also:complete water-meadow, the ground will often require to be broken up and remodelled . This will no doubt be attended with cost; but it should be considered that the first cost is the least. and remodelling the only way of having a complete water-meadow which will continue for years to give See also:satisfaction, To effect a remodelling when the ground is in stubble, let it be ploughed up, harrowed, and cleaned as in a summer See also:fallow, the levelling-boxemployed when required, the stuff from the conductors and main drains spread abroad, and the beds ploughed into shape—all operations that can be performed at little expense . The meadow should be ready by See also:August for sowing with one of the mixtures of grass-seeds already given . But though this plan is ultimately better, it is attended with the one great disadvantage that the soft ground cannot be irrigated for two or three years after it is sown with grass-seeds . This can only be avoided where the ground is covered with old turf which will bear to be lifted . On ground in that See also:state a water-meadow may be most perfectly formed . Let the turf be taken off with the See also:spade, and laid carefully aside for relaying . Let the stript ground then be neatly formed with the spade and See also:barrow, into beds varying in breadth and shape according to the nature of the soil and the See also:dip of the ground—the feeders from the conductor and the small drains to the main drain being formed at the same time . Then let the turf be laid down again and beaten firm, when the meadow will be complete at once, and ready for irrigation . This is the most beautiful and most expeditious method of making a complete water-meadow where the ground is not naturally sufficiently level to begin with . The water should be let on, and trial made of the work, whenever it is finished, and the motion of the water regulated by the introduction of a stop in the conductors and feeders where a change in the motion of the current is observed, beginning at the upper end of the meadow . Should the work be finished as directed by August, a good crop of See also:hay may be reaped in the succeeding summer . There are few pieces of land where the natural descent of the ground will not admit of the water being collected a second time, and applied to the irrigation of a second and lower meadow . In such a case the main drain of a watered meadow may form the conductor of the one to be watered, or a new conductor may be formed by a prolongation of the main drain; but either expedient is only advisable where water is scarce . Where it is plentiful, it is better to supply the second meadow directly from the river, or by a continuation of the first main conductor . In the ordinary catchwork water-meadow, the water is used over and over again . On the steep sides of valleys the plan is easily and cheaply carried out, and where the whole course of the Catch- water is not long the peculiar properties which give it work value, though lessened, are not exhausted when it reaches that part of the meadow which it irrigates last . The See also:design o any piece of catchwork will vary with local conditions, but generally it may be stated that it consists in putting each conduit See also:save the first to the See also:double use of a feeder or distributor and of a drain or See also:collector . In upward or subterranean irrigation the water used rises upward through the soil, and is that which under ordinary circumstances would be carried off by the drains . The system has received considerable development in Germany, where the elaborate method invented b |