The Nile in 1904

At Assuân the Nile has a mean range of 7.90 metres between high and low supply, with a maximum of 9·80 metres and a minimum of 6.40 metres. The high supply varies between 13,200 and 6,500 cubic metres per second, with a mean of 10,000 cubic metres per second, while the low supply varies between 350 and 1400 cubic metres per second with a mean of 590 cubic metres per second. September is generally the highest month and May the lowest. The mean low water level is R. L. 85.00.

At Cairo the Nile has a mean range of 7·00 metres with a maximum of 9·6 metres and a minimum of 5·3 metres. The high supply varies between 12,000 and 4,800 cubic metres per second with a mean of 7,600 cubic metres per second, while the low supply varies between 1,300 and 250 cubic metres per second, with a mean of 500 cubic metres per second. October is the highest month and June the lowest. The mean low water level is at R. L. 12·25.

Tables 41 to 52 refer to the Nile between Assuân and the Barrage at the head of the Delta proper.

Table 46 gives the Reduced Level of the mean low water level of the Nile at various points between Assuân and Cairo. If, for example, it is known that the water surface at any time of the year at Assiout is R. L. 50.80, we know the mean low water by the Irrigation Department levels is 45.05. The gauge is therefore 5.75, and by turning to Table 37 we know the discharge.

Table 37 gives the discharges of the river for gauges referred to the mean low water level. Between Esna and Kena the table is in excess of the truth, and between Assiout and Beni-Suef it is slightly under. Taken all round the table is reliable, calculated from the means of hundreds of discharges and carefully prepared.

Table 45 gives the slope of the water surface of the Nile in flood and in summer between Assuân and Cairo. Owing to the more winding track of the low supply than of the flood waters, the former is 948 kilometres and the flood 900. The slope in summer is ¹⁄₁₃₀₀₀ and in high flood ¹⁄₁₂₂₀₀.

The other tables need no explanation.

23. The Rosetta and Damietta Branches.

—Plates XVII and XVIII give longitudinal sections of the two branches of the Nile and their cross sections are given on Plate XI.

During winter, summer, and low floods, regulation at the Barrage interferes with the natural discharges of the two branches. The Damietta branch is gradually silting up and decreasing in size, while the Rosetta branch scours in high floods. The mean width of the Rosetta branch is 500 metres, and the mean area of the section in flood is 4000 square metres. The mean width of the Damietta branch is 270 metres and the mean section 2700 square metres. The mean velocity of the floods range from 1.00 metre to 1.60 metres per second. In summer the branches are hermetically closed at their heads and receive only the water which filters into them from the subsoil. This in the Rosetta branch amounts to 20 cubic metres per second, and less in the Damietta branch. It may be noted here that at Cairo the girder bridge at Kasr-el-Nil is 403 metres between the abutments and the smaller bridge is 178 metres, making a total width of 581 metres. The width of the Kafr Zayat bridge on the Rosetta branch is 530 metres, while the old Benha bridge on the Damietta branch is 285 metres. The average depth of water in flood in the two branches may be taken as 7 metres.

The barrage at the head of the Rosetta branch has 61 openings of 5 metres each and one lock 15 metres wide and the other 12 metres. They are all open in high flood. The Damietta barrage has 61 openings of 5 metres and one lock of 12 metres. The depth of water in a high flood is 9 metres. The Rosetta barrage has 10 openings too few, and the Damietta barrage 15 openings too many.

Before the construction of the Barrage in the middle of the 19th century, the maximum discharges of the two branches at the head of the Delta were nearly the same. A little lower down, however, the Rosetta branch had considerably more water than the Damietta. About 2 kilometres below the Barrage there was a branch called the Shalakan branch which flowed from the Damietta into the Rosetta branch. About 20 kilometres below the Barrage, the Bahr Ferounieh took about ¹⁄₃ the total discharge of the Damietta branch and led it into the Rosetta branch. Both these were closed by Mehemet Ali, while at the same time the Bahrs Sirsawiah, Baguria, Shebin, Khadrawiah, Moes, Um-Salama, Bohia and Sogair were also completely closed or provided with regulating heads, which very considerably diminished their discharge. During the time that they had been open the Damietta branch had lost water at every kilometre as it approached the sea, and though 400 metres wide at the head it had a channel only 200 metres wide in its lower reaches. The Rosetta branch on the other hand received the tail waters of many Bahrs and had only one escape, the Bahr Saidi near its tail.

The closing of so many escapes on the Damietta branch has caused this branch in its upper reaches to carry so much water that its tail reaches can not carry it without having the surface of the water raised inordinately and dangerously above the level of the country. An examination of the longitudinal sections will show that while the Rosetta branch in its middle reaches is from 1.50 to 2.00 metres above the level of the country in a high flood, the Damietta branch is from 2.50 to 3.00 metres. They will also show how the slope in the early reaches of the Damietta branch is considerably less than that in the early reaches of the Rosetta branch, which results in the gradual silting up of the former as already noted. The Karanain regulator at the head of the old Bahr Shebin, taking from the Damietta branch below the Bahr Ferouniah, was built in 1842 by Linant Pasha, with its wing wall 60 centimetres higher than any previous flood. By 1870 the Damietta branch had risen 70 centimetres above the wing wall as measured by Linant Pasha. In 1878, though the Damietta branch was relieved by the Gizeh breach in the left bank of the Main Nile which drained into the Rosetta branch, the flood water surface of the Damietta branch at Karanain was 1.50 metres above the wing wall.

The maximum, minimum and mean floods in the Rosetta branch are 6,500, 2,600 and 4,000 cubic metres per second. In the Damietta branch they are 4,600, 1,300 and 2,300 cubic metres per second respectively.

CHAPTER III.
The utilisation of the Nile.

24. The Nile in flood.

—We are now in a position to apply our knowledge of the Nile and its tributaries to an examination of the behaviour of the rivers in flood and in time of low supply. Lake Victoria, the Victoria Nile, and Lake Albert may all be considered as the great equatorial regulators of the Nile. The river, as a river, begins at the outlet of Lake Albert, i.e., at the head of the Albert Nile. Generally at its lowest in April, it rises gradually and reaches its maximum in November. The mean minimum of 600 cubic metres per second is gradually increased to its mean maximum of 900 cubic metres. The regulating effect of the lakes is very evident.

Between Lake Albert and Gondokoro the heavier rains begin late in April and with a break in June and July continue to November. The mean minimum discharge of 600 cubic metres per second in April is increased by alternating rises and falls to the mean maximum of 1600 cubic metres per second in September, which has disappeared by the end of November, when the water of Lake Albert alone remains in the river.

The Gazelle river in no way affects the flood or the low supply. Its great function is to maintain the levels of the great swamps between latitudes 7° and 9°, saturate the soil, and prevent the complete disappearance of the waters of the Albert Nile between January and May. The functions this river performs are humble ones, but deprived of its aid, the Nile north of Khartoum would frequently be dry in April and May.

The Albert Nile at its tail just upstream of the mouth of the Sobat is at its lowest in April and May with a mean low discharge of 375 cubic metres per second, when it is joined by the Sobat river with an approximate mean low discharge of 125 cubic metres per second; making a joint discharge for the head of the White Nile of 500 cubic metres per second as a mean minimum. Now begins one of the most interesting operations of any in the whole valley of the Nile, exceeded only in interest by what happens at Khartoum lower down. The Albert Nile and the Sobat river both rise together, the Albert Nile on a very gentle slope freely overflowing its banks in the Sudd region, and the Sobat river confined within its channel during its highest floods. The White Nile has a very gentle slope, little carrying capacity and is quite incapable of taking on both floods. The water rises at the junction and the Sudd region becomes a reservoir flooded to a depth of 3 metres. As the Sobat river increases its discharge gradually from 75 cubic metres per second in April to 1000 cubic metres per second in October and November (for it is confined to its channel), the Albert Nile decreases the actual discharge it sends down the White Nile and increases what it spreads over the Sudd region. The Albert Nile, having increased its quota for the White Nile from 375 in April to 450 cubic metres per second in September, gives less in October and November and gradually passes on its waters in December, January and February when the Sobat has fallen.

The White Nile at its head near Tewfikieh has its mean minimum of 500 cubic metres per second in April, and increases slowly to its mean maximum of 1500 cubic metres per second in December. During this interval its water surface is raised by 3·50 metres. This water travels very slowly on to Khartoum, where the mean minimum is 450 cubic metres per second in May, the slope is very insignificant, and the trough of the river is 1500 metres wide.

At Khartoum the White Nile meets the Blue Nile. No greater contrast exists in the world. If maximum discharges are alone considered, the little finger of the Blue Nile is thicker than the loins of the White Nile.

The Blue Nile is at its lowest on the 1st May with a mean minimum supply of 200 cubic metres per second rising to a mean maximum flood of 10,000 cubic metres per second on the 1st September. The flood has fallen to 2000 cubic metres per second by the middle of November.

Up to the middle of July the Blue and White Niles keep increasing their discharges steadily at Khartoum, but after that date the Blue Nile gauge and discharge rise rapidly together, and the Blue Nile not only feeds the Main Nile, but flows up the White Nile and arrests its discharge, so that at Duem, 200 kilometres above Khartoum, the White Nile discharge decreases in July and August while the Blue Nile is steadily flowing up the White Nile valley and converting it into a reservoir for the Nile in winter. It is only after the 15th September, when the Blue Nile has begun to fall steadily and continuously that the White Nile discharge really commences and reaches its mean maximum of some 2000 cubic metres per second in October.

The mean minimum discharge of the Nile of 650 cubic metres per second at Khartoum is obtained on the 1st May and the mean maximum of 9000 cubic metres per second on the 1st September. Fed by the White Nile reservoir the river falls comparatively slowly. Whether this peculiar relation of the two rivers to each other could not be taken advantage of to increase the supply in December, January and February, and decrease it in October and November by means of a regulating dam built across the White Nile at Khartoum is worthy of study.

I greatly prefer the idea of storing the flood waters of the White Nile at Khartoum to any storage of the Albert Nile water above the junction of the Sobat river. A regulator above the Sobat junction would store up a very considerable quantity of water, but the quality would be very doubtful and possibly dangerous to health.

At El Damer, south of Berber, the Atbara flows into the Nile. Dry from January to May, the flood begins in June and is at its maximum as a rule in the last week of August; with a mean high flood discharge of 3500 cubic metres per second. This water cannot come on to Assuân without filling up the 200 kilometres downstream of the 6th cataract where the slope of the Nile is gentle and the river lends itself to being used as a reservoir. It is owing to the fact that none of the main feeders of the Nile flow in immediately below cataracts that the rise and fall of the Nile in Egypt, is so regular and constant. If the Sobat, Blue Nile and Atbara all flowed into the White or Main Niles below cataracts we should have floods in Egypt whose sudden changes of level and fluctuations would be an unending source of danger to the country.

It is owing to the earliness of the Atbara high flood and the comparative lateness of the Nile high flood, that the ordinary maximum discharge of the Nile at Assuân is only 10,000 cubic metres per second. This is generally on the 5th September. When the monsoon is early the maximum at Assuân is reached before or on the 5th September; when the monsoon is late the maximum is reached about the 20th September. An early maximum at Assuân is generally followed by a low summer, while a late maximum is generally followed by a high summer supply. Only once has this rule been broken and that was in 1891 when there were two maxima, one on the 4th September and another on the 27th. In this year there must have been an extraordinary fall of rain in Abyssinia in September, for the flood of the 27th September was very muddy, while as a rule the river at Assuân is very muddy in August, less so in September, still less so in October and much less in November when the White Nile is the ruling factor in the supply of the river.

If the September rains in Abyssinia are very heavy, an ordinary flood passes Assuân at the end of September and is disastrous for Egypt. This happened in 1878. Table 26 contains details of this flood, of the minimum flood year 1877 and the mean of the 20 years from 1873 to 1892.

At Assuân the Nile enters Egypt, and it now remains to consider it in its last 1,200 kilometres. The mean minimum discharge at Assuân is 590 cubic metres per second and is reached about the end of May. The river rises slowly till about the 20th July and then rapidly through August, reaching its maximum about the 5th September, and then falling very slowly through October and November. The deep perennial irrigation canals take water all the year round, but the flood irrigation canals are closed with earthen banks till the 15th August, and are then all opened. These flood canals, of which there are some 45, are capable of discharging 2,000 cubic metres per second at the beginning of an ordinary year, 3,600 cubic metres per second in a maximum year, and have an immediate effect on the discharge of the Nile. The channel of the Nile itself and its numerous branches and arms consume a considerable quantity of water (the cubic contents of the trough of the Nile between Assuân and Cairo are 7,000,000,000 cubic metres), the direct irrigation from the Nile between Assuân and Cairo takes 50 cubic metres per second, 130 cubic metres per second are lost by evaporation off the Nile, and 400 cubic metres per second by absorption. Owing to all these different causes, there is the net result that, from August 15th to October 1st, the Nile is discharging 2,400 cubic metres per second less at Cairo than Assuân. During October and November the flood canals are closed, and the basins which have been filled in August and September discharge back into the Nile, and in October the Nile at Cairo is discharging 900 cubic metres per second in excess of the discharge at Assuân and 500 cubic metres per second in excess in November.

The mean minimum discharge at Cairo is 500 cubic metres per second and is attained on the 15th of June; the river rises slowly through July and fairly quickly in August, and reaches its ordinary maximum on the 1st October when the basins are full and the discharge from the basins is just beginning. The ordinary maximum discharge at Cairo is about 7,600 cubic metres per second. Through October the Nile at Cairo is practically stationary, and falls rapidly in November.

North of Cairo are the heads of the perennial canals which irrigate the Delta proper. The canals, with their feeders lower down, discharge 1,200 cubic metres per second, and the ordinary maximum flood at Cairo of 7,600 cubic metres per second is reduced by this amount between Cairo and the sea. Of the 6,400 cubic metres per second which remain, 4,100 cubic metres per second find their way to the sea down the Rosetta branch, and 2,300 cubic metres per second down the Damietta branch. During extraordinary floods the Damietta branch has discharged 4,300 cubic metres per second and the Rosetta branch 7,000 cubic metres per second.

25. The Nile in low supply.

—We have so far considered the Nile in flood, it now remains to quickly dispose of the low supply. After reaching its maximum, the Atbara, which is a torrential river, falls more rapidly than others, and by the end of September has practically disappeared; after the middle of September the Blue Nile falls quickly, while the White Nile with its large basin, gentle flow and numerous reservoirs, falls very deliberately. The mean minimum discharge of the White Nile at Gondokoro in an ordinary year, at the time of low supply, is 600 cubic metres per second. Of the Sobat river it is 100 cubic metres per second. By the time the water reaches Khartoum it is reduced to 450 cubic metres per second. The mean low supply of the Blue Nile is 200 cubic metres per second, giving a mean low supply to the Nile at Khartoum of 650 cubic metres per second. The Atbara supplies nothing. Between Khartoum and Assuân there is a further loss of 60 cubic metres per second, and the mean low supply delivered at Assuân is 590 cubic metres per second. In very bad years the discharge at Assuân has fallen to 400 cubic metres per second.

Lombardini was no untrue prophet when he wrote that he was convinced that the more carefully the discharges were taken and the results known, the more would engineers be astonished at the extraordinary amount of the subsoil water which filtered into the Nile from the head of the White Nile to the sea, and which gave back to the Nile in the months of deflux of the river, the water which had percolated into the soil during the afflux. He predicted that heavy as the evaporation was in April, May and June in the Nile valley, the influx of subsoil water would be found to counterbalance it. When we calculate the extent of the water used in irrigation along the course of the Nile, and compare the discharges at Tewfikieh, Khartoum, Assuân, Cairo and at the tails of the Rosetta and Damietta branches during the time of low supply we can only admire the perspicacity of the greatest hydraulic engineer of the last century.

26. Nile water.

—For the following information I am principally indebted to M. J. Barois’ “Les irrigations en Egypte” just published, and to an article by Mr G. P. Foaden in the Journal of the Khedivial Agricultural Society for January 1903. The colour of Nile water is generally a pale yellow, but in June, when the first indications of the coming flood are given by a continuous gentle rise of the river from its minimum gauge, the water changes to green and remains so for two or three weeks. This green water has a very disagreeable taste and odour, and is especially objectionable when the Nile has been very low and the rise is a slow one. In June 1900 it was extraordinarily bad, and the river water was so poor in oxygen that standing on Kasr-el-Nil bridge at Cairo one could see the surface of the water covered with fish which apparently could only live near the surface. In the deep reaches near Kalabsha in Nubia, the fish died in myriads. This green water is attributed by some to the immense amount of vegetable matter brought down by the White Nile from the Sudd region. Some say that it comes principally with the first rise of the Sobat river. But the generally accepted theory to-day is that the green water is the result of vegetable growths from germs is the water itself, and that wherever or whenever the current becomes exceedingly slack they multiply greatly. Upstream of the Assuân dam in June 1903 the water was extraordinarily green and exceedingly objectionable. As it was shot out of the upper sluices of the dam and broken up into spray on the downstream side of the dam it became so purified that I found it difficult to understand that the water flowing past Elephantine Island was what I had seen at Shellal. The green water is followed by the red water of the Nile flood, which has always thoroughly established itself at Cairo by the 1st of August. This red water comes from the scourings of the volcanic plateau of Abyssinia by the Blue Nile and the Atbara. Rich in mud and rich in manures, this red water is the creator of Egypt. Egypt is nothing more than the deposit left by the Nile in flood. The water is most heavily charged with detritus in August, less in September, and still less in October.

Many analyses have been made of Nile water. Following M. Barois, I place side by side the analysis of Dr. Letheby of 1874/75 and Dr. Mackenzie of 1896/97/98. The year 1874 was an extraordinarily high flood.

From this last column M. Barois concludes that in high floods 100,000,000 tons of solid matter pass Assuân, and 88,000,000 in mean floods. It is unfortunate that we have no analyses of low floods like 1877, 88, 99, 1902 and 1904 which were extraordinarily muddy. The water had little sand but much mud. The sand is scoured out of the bed of the river itself in high floods.

After Dr. Letheby the composition of Nile deposit is as follows:—

Comparative analyses of subsoil water in Egypt and Nile water in time of low supply are given below.

It must be remembered that Nile water in the time of low supply consists in a very appreciable part of subsoil water which has filtered into the Nile.

Mr. Foaden states that, speaking in round numbers, we may say that Nile deposit in flood contains

He values the manure deposited by the Nile annually in a well irrigated basin at £·75. He concludes that Nile water in flood is rich in potash, fairly rich in phosphoric acid and poor in nitrogen.

27. The soil of the Nile valley.

—According to numerous analyses made of Egyptian soil in 1872 by MM. Payen, Champion and Gastinel, the soil of Egypt consists of

Some stiff soils contain 84 per cent argile and some light soils contain 68 per cent sand. As one approaches the Mediterranean the quantity of chloride of soda increases and runs from a fraction to 4, 5, and even 10 per cent.

From the means of ten samples of soil from Kena Mudirieh analysed for me in May by Mr. Frank Hughes of the Agricultural Society we gather that the constituents of the soil are as follows:—

We have here a general sufficiency of phosphoric acid, plenty of potash and lime, and a low proportion of nitrogen.

The salts of the soil, when in excess, are chlorides and sulphates of soda: the carbonates are present in very small quantities indeed.

The following selection from a paper by Mr. Lang Anderson in the December 1903 number of the Journal of the Khedivial Agricultural Society is interesting.

“Voelcker’s analyses of the two samples of soil taken from the drained bed of what was Lake Edku near Alexandria give the following results:—

28. Basin irrigation.

—Considering the times of flood and low supply, the climate of Egypt, the turbidity of the Nile flood, and the deltaic formation of the Nile valley, no better system than basin irrigation as practiced in Egypt could possibly have been devised. If the flood had come in April and May and been followed by a burning summer, or if the actual autumn floods had been followed by the frozen winters of Europe or the warm winters of the Sudan, basin irrigation would have been a failure or a very moderate success; but, given the Egyptian climate, basin irrigation has stood without a rival for 7000 years.

Basin irrigation, as it has been practised in Egypt for thousands of years, is the most efficacious method of utilising existing means of irrigation which the world has witnessed. It can be started by the sparsest of populations. It will support in wealth a multitude of people. King Menes made his first dyke when the Egyptian nation was in its infancy. Egypt, in Roman times, supported a population twice as dense as that of to-day. The direct labour of cultivation is reduced to an absolute minimum.

Shakespeare’s genius has crystallised the system for all time:—

If we cast back our view to the dawn of Egyptian history, we can picture the Nile Valley as consisting of arid plains, sand dunes, and marshy jungles, with reclaimed enclosures on all the highest lands. Every eight or ten years the valley was swept by a mighty inundation. The seeds of future success lay in the resolve of King Menes’ engineers to confine their attention to one bank of the river alone. It was the left bank of the river which history tells us was first reclaimed. A longitudinal dyke was run parallel to the stream, and cross dykes tied it to the Lybian hills. Into these basins or compartments the turbid waters of the flood were led by natural water-courses and artificial canals and allowed to deposit their rich mud and thoroughly saturate the soil; and meantime the whole of the right bank and the trough of the river itself were allowed to be swept by the floods. It must have been on this wild eastern bank that were conducted all the hippopotamus hunts which are crowded on the wall pictures of buildings of the early dynasties. In all probability, the first six dynasties contented themselves with developing the left bank of the Nile. As, however, the population increased, and with it the demand for new lands, it became necessary to reclaim the right bank of the river as well. The task now was doubly difficult, as the river had to be confined to its own trough. This masterful feat was performed by the great Pharaohs of the XIIth Dynasty, the Amenemhats and the Usartsens, who, under the name of Sesostris, usurped the place of Menes in the imagination of the ancient world. They were too well advised to content themselves with repeating on the right bank what Menes had done on the left. By suddenly confining the river they would have exposed the low-lying lands of Memphis and Lower Egypt to disastrous inundations. To obviate this, they widened and deepened the natural channel which led to the Fayoum depression in the Lybian hills, and converted it into a powerful escape to carry off the excess waters of high floods; and so successful were they in their undertakings that the conversion of the Fayoum depression into Lake Mœris was long considered by the ancient world as one of its greatest wonders. They led the flood into the depression when it was dangerously high, and provided for its return to the river when the inundation had come to an end. By this means, they insured the lake against being at a high level during a period of flood. The gigantic dykes of entry and exit were only cut in times of emergency, and were reconstructed again at an expense of labour which even an Egyptian Pharaoh considered excessive. To understand how capable Lake Mœris was to control the floods, and turn a dangerous into a beneficial inundation, I should recommend a study of Sir Hanbury Brown’s “Fayoum and Lake Mœris.” As years rolled on the Nile widened and deepened its own trough, to which it was now confined; and, eventually, the time came when Lake Mœris could be dispensed with without danger. It was gradually reclaimed and converted into the Fayoum with its 350,000 acres of cultivated land.

Basin irrigation holds the flood waters for some 45 days per annum over the whole of the valley. The water is in places 3 metres deep, and in others only 30 centimetres deep, while the average depth is about 1 metre. Now the retention of this water over the land for a period of six weeks permits of the thorough saturation of the subsoil in places where the subsoil is of proper consistency; and this water can be drawn on, in winter and summer, for maturing certain crops and growing others. It was where the subsoil gave a plentiful supply of water, and permitted of intense cultivation throughout the year, that we find all the ancient capitals of Egypt. Abydos has the finest subsoil water in the Nile Valley; Memphis has an excellent supply; while Thebes has the only good subsoil water on the whole of the right bank. Good subsoil water was to the ancient Egyptian world what the presence of a rich gold mine is to one of our new colonies.

Subsoil water supplies the link between basin and perennial irrigation. It explains the reason why modern Egypt is not satisfied with the irrigation which has come down from the remotest antiquity, but is desirous of conferring on the length and breadth of the Nile Valley those advantages which gave Abydos, Memphis, and Thebes their pre-eminence in the past. Any country which possesses rivers and streams whose waters are in flood for six weeks per annum at a suitable season of the year can betake itself to basin irrigation with more or less profit. The science of dams, weirs, and regulators has received such development during recent years that there can be no problem so difficult that it cannot be solved by experience and originality. Basin irrigation allows of the thorough development of countries whose streams have short and turbid floods which precede a fairly cool season; whether such irrigation be the stately irrigation of the Nile Valley, perfected by the science and experience of 7,000 years; or the less perfect, but still highly developed and river-fed tank systems of Madras; or the primitive, but effective basins of Bundelkund, where the impounded water irrigates the crops on the down-stream sides of the basins for one season, and then allows of the basins themselves being dried and cultivated in the next.

The Nile in high flood rises 10 metres above its bed, in a mean flood 9 metres and in a poor flood 7¹⁄₂ metres. The beds of the main basin canals are about 4¹⁄₂ metres, and the cultivated land at the river’s edge about 9 metres above the river-bed. The basins have an average area of 7,000 acres. Where the valley is narrow, they average 2,000 acres each, and where it is wide 20,000 acres; while some of the tail basins are 40,000 acres in extent. Each canal has about seven or eight basins depending on it, of which the last is always the largest. There are masonry regulators at the canal heads, at each crossing of the cross banks, and at the tail escapes into the river. In the more perfect basins the canals and escapes syphon under one another and overlap and supply each other’s deficiencies, so as to meet the requirements of every kind of flood which Egypt can experience. Colonel Ross’s work on the basin irrigation of Egypt is a monument of patient observation and a storehouse of information. Some of the canals like the Sohagia on Plate XIV are veritable rivers, discharging 450 cubic metres per second; but a good average canal discharges 30 cubic metres per second. The largest canal has a width of 75 metres, while the average width is 9 metres. Good basin canals discharge in an average year one cubic metre per second per 700 acres. Forty-five days suffice for a perfect irrigation. The cost of providing basin irrigation in Egypt for basins of 10,000 acres may be taken at £3 per acre thus made up:—Banks, £1·50.; canals, £·75.; masonry works, £·50.; and bank protection, £·25. If the basins are under 5,000 acres, the cost will be nearly double this. The annual cost of maintenance is £·10 per acre; while the lands themselves are rented at £3 per acre. In well irrigated basins no manures are needed, and alternate crops of cereals and legumins have been reaped for centuries without the land having been exhausted in any way whatever. Where the subsoil water is good and double cropping resorted to, then manures have to be applied.

29. Perennial Irrigation.

—The foundation-stone of the conversion of the whole of Egypt from basin to perennial irrigation was laid by Mehemet Ali in 1833, when he began the construction of the Barrages across the Nile branches north of Cairo. These weirs were intended to raise the summer level of the Nile by 3 metres. As the ordinary summer level of the Nile was 1.50 metres above its bed, the weirs were expected to raise it 4.50 metres above the Nile bed. The old basin canals had to be considerably deepened to take in the summer supplies; while in other parts new perennial canals were dug. Perennial irrigation requires canals capable of discharging 1 cubic metre per second per 3500 acres, as against 700 acres for basin irrigation. Some of the perennial canals are very capacious. The two largest discharge 700 and 450 cubic metres per second respectively. There are no artificial canals in the world like them. All the canals are liberally provided with regulators and locks. The energies of the Irrigation Department during the last ten years have been chiefly directed to the provision of sufficient drains to meet that over-saturation of the soil, which all but the best regulated perennial irrigation invariably entails. After many years’ experience in India and Egypt, we are convinced that the construction of drains and escapes should precede, and not follow the canals. It seems fatuous for engineers to be always over-saturating and half-ruining tens of thousands of acres of low-lying lands, during the improvement of hundreds of thousands of acres of high-lying lands, when it would be perfectly easy, with a little foresight, to secure all the advantages without piling up disadvantages. The drains have generally one-third the capacity of the canals. Dry crops require 1 cubic metre per second per 3500 acres; and rice requires the same per 2000 acres. The drains in dry-cropped lands provide for 1 cubic metre per second per 10,000 acres, and in rice lands 1 cubic metre per second per 6000 acres.