466 



NA TURE 



[September 7, 1905 



subject is water — living, life-giving water. It can surely 

 never be a dry subject ; but we all know that with the best 

 text to preach on the preacher may be as dry as dust. 



Irrigation : What it Means. 



Irrigation may be defined as the artificial application of 

 water to land for the purposes of agriculture. It is, then, 

 precisely the opposite of drainage, which is the artificial 

 removal of water from lands which have become saturated, 

 to the detriment of agriculture. A drain, like a river, goes 

 on increasing as affluents join it. An irrigation channel 

 goes on diminishing as water is drawn off it. Later on 

 I shall show you how good irrigation should always be 

 accompanied by drainage. 



In lands where there is abundant rainfall, and where it 

 falls at the right season of the year for the crop \vhich it 

 is intended to raise, there is evidently no need of irrigation. 

 But it often happens that the soil and the climate are 

 adapted for the cultivation of a more valuable crop than 

 that which is actually raised, because the rain does not 

 fall just when it is wanted, and there we must take to 

 artificial measures. 



In other lands there is so little rain that it is practically 

 valueless for agriculture, and there are but two alternatives 

 — irrigation or desert. It is in countries like these that 

 irrigation has its highest triumph ; nor are such lands 

 always to be pitied or despised. The rainfall in Cairo is 

 on an average 14 inches per annum, yet lands purely agri- 

 cultural are sold in the neighbourhood as high as 150!. an 

 acre. 



This denotes a fertility perhaps unequalled in the case of 

 any cultivation depending on rain alone, and this in spite 

 of the fact that the Egyptian cultivator is in many respects 

 very backward. The explanation is not far to seek. All 

 rivers in flood carry along much more than water. Some 

 carry alluvial matter. Some carry fine sand. Generally 

 the deposit is a mixture of the two. I have never heard 

 of any river that approached the Nile in the fertilising 

 nature of the matter borne on its annual floods ; with the 

 result that the plains of Egypt have gone on through all 

 ages, with the very minimum of help from foreign manures, 

 yielding magnificent crops and never losing their fertility. 

 Other rivers bring down little but barren sand, and any 

 means of keeping it off the fields should be employed. 



Primitive Means of Irrigation. 

 The earliest and simplest form of irrigation is effected 

 bv raising water from a lake, river, or well, and pouring 

 it over the land. The water may be raised by any me- 

 chanical power, from the brawny arms of the peasant to 

 the newest pattern of pump. The earliest Egyptian sculp- 

 tures show water being raised by a bucket attached to one 

 end of a long pole, turning on an axis with a heavy counter- 

 poise at the other end. In Egypt this is termed a shadoof, 

 and to this day, all along the Nile banks, from morning 

 to night brown-skinned peasants may be seen watering their 

 fields in precisely this way. Tier above tier they ply their 

 work so as to raise water 15 or 16 feet on to their land. 

 By this simple contrivance it is not possible to keep more 

 than about 4 acres watered by one shadoof, so you may 

 imagine what an army is required to irrigate a large 

 surface. Another method, largely used by the natives of 

 Northern India, is the shallow bucket suspended between 

 two strings, held by men who thus bale up the water. A 

 step higher is the water-wheel, with buckets or pots on 

 an endless chain around it, worked by one or a pair of 

 bullocks. This is a very ordinary method of raising the 

 water throughout the East, where the water-wheel is of 

 the rudest wooden construction and the pots are of rough 

 earthenware. Yet another method of water-raising is very 

 common in India from wells where the spring level may 

 be as deep as 100 feet or more. A large leathern bag is 

 let down the well by a rope passing over a pulley and 

 raised by a pair of bullocks, which haul the bag up as they 

 run down a slope the depth of the well. An industrious 

 farmer with a good well and three pairs of good bullocks 

 can keep as much as 12 acres irrigated in Northern India, 

 although the average is much less there. The average cost 

 of a masonry well in India varies from 20I. to 40Z., accord- 

 ing to the depth required. But it is obvious that in many 

 places the geological features of the country are such that 



NO. 1871, VOL, 72] 



well-sinking is impracticable. The most favourable con- 

 ditions are found in the broad alluvial plains of a deltaic 

 river, the subsoil of which may be counted on as contain- 

 ing a constant supply of water. 



Pumps and Windmills. 

 All these are the primitive water-raising contrivances of 

 the East. Egypt has of late been more in touch with 

 Western civilisation, and since its cotton and sugar-cane 

 crops yield from 6/. to 8/. or even lol. per acre, the well- 

 to-do farmer can easily afford a centrifugal pump %vorked 

 by steam power. Of these there are now many hundreds, 

 fixed or portable, working on the Nile banks of Egypt. 

 Where wind can be counted on the windmill is a very 

 useful and cheap means of raising water. But everything 

 depends on the force and the trustworthiness of the 

 wind. In the dry Western States of America wind power 

 is largely used for pumping. It is found that this power 

 is of little use if its velocity is not at least six miles per 

 hour. (The mean force of the wind throughout the whole 

 United States is eight miles per hour.) Every windmill, 

 moreover, should discharge its water into a tank. It is 

 evident that irrigation cannot go on without cessation day 

 and night, and it may be that the mill is pumping its best 

 just when irrigation is least wanted. The water should, 

 therefore, be stored till required. In America it is found 

 that pumping by wind power is about two-thirds of the cost 

 of steam power. With a reservoir 5 to 15 acres may be 

 kept irrigated by a windmill. Without a reservoir 3 acres 

 is as much as should be counted on. Windmills attached 

 to wells from 30 to 150 feet deep cost from 30/. to 70/. 



Artesian Wells. 



Up to now the artesian well cannot be counted on as of 

 great value for irrigation. In the State of California there 

 are said to be 8097 artesian wells, of a mean depth of 

 210 feet, discharge 012 cubic feet per second, and original 

 cost on an average 50/. Thirteen acres per well is a large 

 outturn. 



In Algeria the French have bored more than 800 artesian 

 wells, with a mean depth of 142 feet, and they are said 

 to irrigate 50,000 acres. But these are scattered over a 

 large area. Otherwise, the gathering ground would prob- 

 ably yield a much smaller supply to each well than it now 

 does. In Queensland artesian wells are largely used for 

 the water supply of cattle stations, but not for irrigation. 



Well Irrigation. 

 It is evident that where water has to be raised on to the 

 field there is an outlay of human or mechanical power which 

 may be saved if it can be brought to flow over the fields 

 by gravitation. But there is one practical advantage in 

 irrigating with the water raised from one's own well or 

 from a river. It is in the farmer's own hands. He can 

 work his pump and flood his lands when he thinks best. 

 He is independent of his neighbours, and can have no dis- 

 putes with them as to when he may be able to gel water 

 and when it may be denied to him. In Eastern countries, 

 where corruption is rife among the lower subordinates of 

 government, the farmer who sticks to his well knows that 

 he will not require to bribe anyone ; and so it is that in 

 India about 13 millions of acres, or 30 per cent, of the 

 whole annual irrigation, is effected by wells. Government 

 may see fit to make advances to enable the farmer to find 

 his water and to purchase the machinery for raising it ; or 

 joint-stock companies may be formed with the same object. 

 Beyond this all is in the hands of the landowner himself. 



Canal Irrigation. 



Irrigation on a large scale is best effected by diverting 

 water from a river or lake into an artificial channel, and 

 thence on to the fields. If the water surface of a river 

 has a slope of 2 feet per mile, and a canal be drawn from 

 it with a surface slope of i foot per mile, it is evident that 

 at the end of a mile the water in the canal will be i foot 

 higher than that in the river ; and if the water in the river 

 is 10 feet below the plain, at the end of 10 miles the 

 water in the canal will be flush with the plain, and hence- 

 forth irrigation can be effected by simple gravitation. 



When there is no question of fertilising deposit, and only 

 pure water is to be had, the most favourable condition of 



