468 



NA TURE 



[September 7, 1905 



Elsewhere there are rivers in India, rising in districts 

 subject to certain heavy periodical rainfall, and carrying 

 their vi-aters on to distant plains of very uncertain rain- 

 fall. At a small expense channels can sometimes be con- 

 structed drawing off from the flooded river water sufficient 

 thoroughly to saturate the soil, and render it fit to be 

 ploughed up and sown with wheat or barley, which do not 

 require frequent watering. The canal soon dries up, and 

 the sown crop must take its chance ; but a timely shower 

 of rain may come in to help it, or well irrigation may 

 mature the crop. These, which are known in India as 

 inundation canals, are of high value. 



Southern India. 



In Southern India there are three great rivers, drawing 

 their supply from the line of hills called the Ghats, running 

 parallel to and near the western coast, and after a long 

 course discharging into the Bay of Bengal on the east 

 coast. Against the Ghats beats the whole fury of the 

 tropical S.W. monsoon, and these rivers for a few months 

 are in high flood. As they approach the sea they spread 

 out in the usual deltaic form. Dams have been built across 

 the apex of these deltas, from which canals have been 

 drawn, and the flood waters are easily diverted over the 

 fields, raising a rice crop of untold value in a land where 

 drought and famine are too common. But for the other 

 months of the year these rivers contain very little water, 

 and there is now a proposition for supplementing them 

 with very large reservoirs. 



A very bold and successful piece of irrigation engineering 

 was carried out a few years ago in South India, which 

 deserves notice. A river named the Periyar took its rise 

 in the Ghats, and descended to the sea on the west coast, 

 where there was no means of utilising the water, and a 

 good deal of money had periodically to be spent in con- 

 trolling its furious floods. A dam has now been built 

 across its course, and a tunnel has been made through the 

 mountains, enabling the reservoir to be discharged into a 

 system of canals to the east, where there is a vast plain 

 much in need of water. 



In the native State of Mysore, in Southern India, there 

 are on the register about 40,000 irrigation reservoirs (or 

 tanks, as they are called), or about three to every four 

 square miles, and the nature of the country is such that 

 hundreds may be found in the basin of one river — small 

 tanks in the upper branches and larger ones in the lower, 

 as the valley widens out — and these require constant watch- 

 ful attention. From time to time tropical rainstorms sweep 

 over the country. If then even a small tank has been 

 neglected, and rats and porcupines have been allowed to 

 burrow in the dam, the flood may burst through it, and 

 sweep on and over the dam of the next village, lower down. 

 One dam may then burst after another, like a pack of 

 cards, and terrible loss occurs. 



In this State of Mysore a very remarkable irrigation 

 reservoir is now under construction at a place called Mari 

 Kanave. Nature seems here to have formed an ideal site 

 for a reservoir, so that it is almost irresistible for the 

 engineer to do his part, even although irrigation is not so 

 badly wanted here as elsewhere. The comparatively narrow 

 neck of a valley containing 2075 square miles is being 

 closed by a masonry dam 142 feet high. The reservoir 

 thus formed will contain 30.000 million cubic feet of water, 

 but it is not considered that it will fill more than once 

 in thirty years. Nor is there irrigable land requiring so 

 great a volume of water. Much less would be sufficient, 

 so such a high dam is not needed ; but the construction 

 of a waste weir to prevent the submergence of a lower dam 

 would require such heavy excavation through one of the 

 limiting hills that it is cheaper to raise the dam and utilise 

 a natural hollow in the hillside for a waste weir. 



Irrigation in Egypt. 

 No lecture on irrigation would be complete without 

 describing what has been done in Egypt. You are gene- 

 rally familiar with the shape of that famous little country. 

 Egypt proper extends northwards from a point in the Nile 

 about 780 miles above Cairo — a long valley, never eight 

 miles wide, sometimes not half a mile. East and west 

 of this lies a country broken into hills and valleys, wild 



NO. 1 87 I, VOL. 72] 



crags, level stretches, but everywhere absolutely sterile, dry 

 sand and rock, at such a level that the Nile flood has 

 never reached it to cover its nakedness with fertile deposit. 

 A few miles north of Cairo the river bifurcates, and its 

 two branches flow each for about 130 miles to the sea. As 

 you are probably aw-are, with rivers in a deltaic state the 

 tendency is for the slope of the country to be away from 

 the river, and not towards it. In the Nile Valley the river 

 banks are higher than the more distant lands. From an 

 early period embankments were formed along each side of 

 the river, high enough not to be topped by the highest 

 flood. At right angles to these river embankments others 

 were constructed, dividing the whole valley into a series 

 of oblongs, surrounded on three sides by embankments, on 

 the fourth by the desert heights. These oblong areas vary 

 from about 50,000 to 3000 acres. I have said the slope of 

 the valley is away from the river. It is easy, then, when 

 the Nile is low, to cut short deep canals in the river banks, 

 which fill as the river rises and carry the precious mud- 

 charged water into these great flats. There the water 

 remains for a month or more, some three or four feet 

 deep, depositing its mud, and then at the end of the flood 

 it may either be run off direct into the receding river, or 

 cuts may be made in the cross embankments and the 

 water passed off one flat after another, and finally rejoin 

 the river. This takes place in November, when the river 

 is rapidly falling. Whenever the flats are firm enough to 

 allow a man to walk over them with a pair of bullocks, 

 the mud is roughly turned over with a wooden plough, or 

 even the branch of a tree, and wheat or barley is imme- 

 diatelv sown. So soaked is the soil after the flood that 

 the seed germinates, sprouts, and ripens in April without 

 a drop of rain or any more irrigation, except what, perhaps, 

 the owner may give from a shallow well dug in the field. 

 In this manner was Egypt irrigated up to about a century 

 ago. The high river banlis which the flood could not 

 cover were irrigated directly from the river, the water being 

 raised as I have already described. 



The Barrage. 



With the last century, however, appeared a very striking 

 figure in Egyptian history, Muhammed Ali Pasha, who 

 came from Turkey a plain captain of infantry, and before 

 many years had made himself master of the country, yield- 

 ing only a very nominal respect to his suzerain lord, the 

 Sultan at Constantinople. 



Muhammed Ali soon recognised that with this flood 

 system of irrigation only one cereal crop was raised in the 

 year, while with such a climate and such a soil, with a 

 teeming population and with the markets of Europe so 

 near, something far more valuable might be raised. Cotton 

 and sugar-cane w'ould fetch far higher prices ; but they 

 could only be grown at a season when the Nile is low, and 

 they must be watered at all seasons. The water-surface 

 at low Nile is about 25 feet below the flood-surface, or 

 more than 20 feet below the level of the country. A canal, 

 then, running 12 feet deep in the flood would have its bed 

 13 feet above the low-water surface. Muhammed Ali 

 ordered the canals in Lower Egypt to be deepened ; but 

 this was an enormous labour, and as they were badly laid 

 out and graded they became full of mud during the flood 

 and required to be dug out afresh. Muhammed Ali was 

 then advised to raise the water-surface by erecting a dam 

 (or, as the French called it, a barrage) across the apex 

 of the delta, twelve miles north of Cairo, and the result 

 was a very costly and imposing work, which it took long 

 years and untold wealth to construct, and which was no 

 sooner finished than it was condemned as useless. 



Egyptian Irrigation since the English Occupation. 

 With the English occupation in 1883 came some English 

 engineers from India, who, supported by the strong arm 

 of Lord Cromer, soon changed the situation. The first 

 object of their attention was the barrage at the head of 

 the delta, which was made thoroughly sound in six years 

 and capable of holding up 15 feet of water. Three great 

 canals were taken from above it, from which a network 

 of branches are taken, irrigating the province to the left 

 of the western, or Rosetta branch of the river, the two 

 provinces between the branches, and the two to the right 

 of the eastern, or Damietta branch. 



