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.
| Month. | PARTS IN 100,000 OF WATER | ||
|---|---|---|---|
| Dr. Mackenzie. | Dr. Letheby. | The Mean of the two | |
| January | 31·0 | 16·7 | 27·4 |
| February | 25·3 | 12·6 | 22·1 |
| March | 12·7 | 5·3 | 10·9 |
| April | 15·8 | 6·6 | 13·5 |
| May | 14·7 | 4·8 | 12·2 |
| June | 14·1 | 6·9 | 12·3 |
| July | 13·9 | 17·8 | 14·8 |
| August | 159·0 | 149·2 | 156·6 |
| September | 156·1 | 53·3 | 130·4 |
| October | 110·0 | 37·8 | 92·8 |
| November | 70·8 | 34·4 | 61·7 |
| December | 47·0 | 28·9 | 42·4 |
| Mean | 56·0 | 31·3 | 49·8 |
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:—
| In flood. | In low supply. | |
|---|---|---|
| Organic matter | 15·02 | 10·37 |
| Phosphoric acid | 1·78 | ·57 |
| Lime | 2·06 | 3·18 |
| Magnesia | 1·12 | ·99 |
| Potash | 1·82 | 1·06 |
| Soda | ·91 | ·62 |
| Alumina and oxide of iron | 20·92 | 23·55 |
| Silica | 55·09 | 58·22 |
| Carbonic acid and loss | 1·28 | 1·44 |
| Total | 100·00 | 100·00 |
Comparative analyses of subsoil water in Egypt and Nile water in time of low supply are given below.
| Dissolved matter. | PARTS IN 100,000 | |
|---|---|---|
| Well water. | Summer water in Nile. | |
| Lime | 16·56 | 4·24 |
| Magnesia | 4·53 | 1·00 |
| Soda | 8·20 | 6·20 |
| Potash | ·37 | 1·44 |
| Chlorine | 13·60 | ·67 |
| Sulphuric acid | 5·93 | 2·16 |
| Nitric acid | ·17 | Traces |
| Silica, alumina and oxide of iron | 1·80 | ·97 |
| Organic Matters | ·60 | 1·75 |
| Carbonic oxide and loss | 12·26 | 4·03 |
| 64·02 | 22·46 | |
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.