September 7, 1905] 



NATURE 



469 



In Upper Egypt, with one very important exception (the 

 lbr;ihiniieh Canal, which is a perennial one), the early 

 flood system of irrigation, yielding one crop a year, pre- 

 vailed until very recently, but it was immensely improved 

 after the British occupation by the addition of a great 

 number of masonry head sluices, aqueducts, escape weirs, 

 &c., on which some 800,000!. was spent. With the com- 

 pletion of these works, and of a complete system of drain- 

 age, to be alluded to further on, it may be considered that 

 the irrigation system of Egypt was put on a very satisfactory 

 basis. There was not much more left to do, unless the 

 volume of water at disposal could be increased. 



Probably no large river in the world is so regular as the 

 Nile in its periods of low supply and of flood. It rises 

 steadily in June, July, and August. Then it begins to go 

 down, at first rapidly, then slowly, till the following June. 

 It is never a month before its time, never a month behind. 

 It is subject to no e.xceptional floods from June to June. 

 Where it enters Egypt the difference between maximum and 

 minimum Nile is about 25 feet. If it rises 35 feet higher 

 the country is in danger of serious flooding. If in former 

 days its rise was 6 feet short of the average there existed 

 a great risk that the floods would not cover the extensive 

 flats of Upper Egypt, and thus the ground would remain 

 as hard as stone, and sowing in November would be im- 

 possible. Fortunately the good work of the last twenty 

 years very much diminishes this danger. 



The Assuan Dam and Reservoir. 



In average years the volume of water flowing past Cairo 

 in September is from thirty-five to forty times the volume 

 in June. By far the greater part of this flood flows out to 

 the sea useless. How to catch and store this supply for 

 use the following May and June was a problem early 

 pressed on the English engineers in Egypt. 



During the time of the highest flood the Nile carries along 

 with it an immense amount of alluvial matter, and when 

 it was first proposed to store the flood-water the danger 

 seemed to be that the reservoir would in a few years be 

 filled with deposit, as those I have described in India. 

 Fortunately it was found that after November the water 

 was fairly clear, and that if a commencement were made 

 even as late as that there would still be water enough 

 capable of being stored to do enormous benefit to the 

 irrigation. 



A site for a great dam was discovered at Assuan, 600 

 miles south of Cairo, where a dyke of granite rock crosses 

 the valley of the river, occasioning what is known as the 

 First Cataract. On this ridge of granite a stupendous 

 work has now been created. A great wall of granite 6400 

 feet long has been thrown across the valley, 23 feet thick 

 at the crest, 82 feet at the base. Its height above the 

 rock-bed of the river is 130 feet. This great wall or dam 

 holds up a depth of 66 feet of water, which forms a lake 

 of more than 100 miles in length up the Nile Valley, con- 

 taining 38,000 million cubic feet of water. 



The dam is pierced with 180 sluices, or openings, 

 through which the whole Nile flood, about 360,000 cubic 

 feet per second, is discharged. A flight of four locks, 

 each 260x30 feet, allows of free navigation past the dam. 

 The foundation-stone of this great work was laid in 

 February 1899, and it was completed in less than four 

 years. At the same time a very important dam of the 

 pattern of the barrage north of Cairo was built across 

 the Nile at Assiut, just below the head of the Ibrahimieh 

 Canal, not with the object of storing water, but to enable 

 a requisite supply at all times to be sent dowii that 

 ■canal. 



The chief use of the great Assuan reservoir is to enable 

 perennial irrigation, such as exists in Lower Egypt, to be 

 substituted in Upper Egypt for the basin system of water- 

 ing the land only through the Nile flood ; that is, to 

 enable two crops to be grown instead of one every year, 

 and to enable cotton and sugar-cane to take the place 

 of wheat and barley. But a great deal more had to be 

 done in order to obtain the full beneficial result of the 

 work. About 450,000 acres of basin irrigation are now 

 being adapted for perennial irrigation. Many new canals 

 "have had to be dug, others to be deepened. Many new 

 masonry works have had to be built. It is probable the 



NO. 187 I, VOL. 72] 



works will be finished in 1908. There will then have been 

 spent on the great dam at Assuan, the minor one at 

 Assiut, and the new canals of distribution in Upper Egypt 

 about six and a half millions sterling. For this sum the 

 increase of land rental will be about 2,637,000/., and its 

 sale value will be increased by about 26,570,000!. 



Drainage. 

 In the great irrigation systems which I have been 

 describing, for a long time little or no attention was paid 

 to drainage. It was taken for granted that the water 

 would be absorbed or evaporated, and get away some- 

 how without doing any harm. This may hold good for 

 high-lying lands, but alongside of these are low-lying 

 lands into which the irrigation water from above will 

 percolate and produce waterlogging and marsh. .Along 

 with the irrigation channel should be constructed the 

 drainage channel, and Sir W. Willcocks, than whom there 

 is no better authority on this subject, recommends that 

 the capacity of the drain should be one-third that of the 

 canal. The two should be kept carefully apart — the canal 

 following the ridges, the drain following the hollows of 

 the country, and one in no case obstructing the other. 

 This subject of drainage early occupied the attention of 

 the English engineers in Egypt. In the last twenty years 

 many hundred miles of drains have been excavated, some 

 as large as 50 feet width of bed and 10 feet deep. 



Irrigation in America. 

 If it is to Italy that we should look for highly finished 

 irrigation works and careful water distribution, and to 

 India and Egypt for widespreading tracts of watered land, 

 it is to America that we naturally look for rapid progress 

 and bold engineering. In the Western States of America 

 I there is a rainfall of less than 20 inches per annum, the 

 consequence of which is a very rapid development of 

 irrigation works. In i88g the irrigation of these Western 

 States amounted to 3,564,416 acres. In 1900 it amounted 

 to 7,539,54s acres. Now it is at least 10,000,000 acres. 

 The land in these States sells from los. to il. per acre if 

 unirrigated. With irrigation the same land fetches SI. 10s. 

 per acre. The works are often rude and of a temporary 

 nature, the extensive use of timber striking a foreigner 

 from the Old World. Some of the American canals are 

 on a large scale. The Idaho Company's canal discharges 

 2585 cubic feet, the Turlook Canal in California 1500 

 cubic feet, and the North Colorado Canal 2400 cubic feet 

 per second. These canals have all been constructed by 

 corporations or societies, in no case by Government. On 

 an average it has cost about 32s. per acre to bring the 

 water on to the land, and a water-rate is charged of 

 from 2/. 8s. to 4/. per acre, the farmer paying in addition 

 a rate of from 2S. to los. per acre annually for mainten- 

 ance. Distributary channels of less than 5 feet wide cost 

 less than 100/., up to 10 feet wide about 150!. per mile. 



The Introduction of Irrigation into a Country. 



It is evident that there are many serious considerations 

 to be taken into account before entering on any large 

 project for irrigation. Statistics must be carefully collected 

 of rainfall, of the sources of water supply available, and 

 of the amount of that rainfall which it is possible to store 

 and utilise. The water should be analysed if there is 

 any danger of its being brackish. Its temperature should 

 be ascertained. It should be considered what will be the 

 elTect of pouring water on the soil, for it is not always 

 an unmixed benefit. A dry climate may be changed into 

 a moist, and fever and ague may follow. In India there 

 are large tracts of heavy black soil, which with the 

 ordinary rainfall produce excellent crops nine years out 

 of ten, and where irrigation would rather do harm than 

 good. ' But in the tenth year the rains fail, and without 

 artificial irrigation the soil will yield nothing. So terrible 

 may be the misery caused by that tenth year of drought 

 that even then it might pay a Government to enter on a 

 scheme of irrigation. But it is evident that it might not 

 pay a joint-stock company. 



in all cases it is of the first importance to establish by 

 law the principle that all rivers or streams above a certain 

 size are national property, to be utilised for the good of 



