41. Dakhla oasis.
—This, by far the most important and prosperous of the Egyptian oases, lies three days’ march west of Kharga, or about 300 kilometres due west of Armant in the Nile valley. The site is a depression lying at the foot of the great east and west Cretaceous escarpment, bounded to the south by the undulating desert of Nubian sandstone, which stretches unchanged almost to the heart of the continent. The inhabitants of Dakhla, numbering over 17,000, are distributed among 12 villages and form a practically self-supporting community. The cultivable land within the oasis (400 square kilometres) amounts to nearly 50,000 acres, of which one half is under cultivation; in addition several extensive areas of alluvium covered ground exist outside the oasis proper, notably on the Gabbari road between Dakhla and Kharga. Owing to the difficulty of drainage, salines, saltyland, marshes and pools occupy some 7,000 acres.
There are nearly 130,000 adult palm trees in Dakhla, a large export trade in dates being carried on with the Nile valley; the finest crops of wheat and barley are raised, while the fruits of the oasis, oranges, apricots, mulberries, etc., are abundant and of excellent quality.
Taxes are levied as follows:—(1) Mature date-palms are taxed 11⁄2 piastres each per annum; (2) Modern wells (i.e. biyâr, made with the existing boring plant) pay 50 piastres per annum per qirat of water; (3) Ancient wells (aiyûn) pay the same, except that in some cases those used for irrigating palmgroves are exempt. There are 71⁄2 trees and 11⁄2 acres per inhabitant, and the total tax paid by the community is about £E. 2,500.
The water-supply of the oasis is derived from an underground bed of sandstone, 55 metres thick, underlying a dense impervious red clay 45 metres in thickness; the upper part of the latter is conspicuous throughout the oasis, underlying the alluvium and forming the base of the surrounding escarpments in many localities. Below the water-bearing sandstone lies a black clay, never yet penetrated by the boring rods; it is probable that other water-tables exist below and such would be invaluable for the irrigation of those parts of the oasis where the present supply is unsatisfactory. There seem to be no natural springs extant at the present day, the whole of the water-supply being through boreholes, both ancient and modern. The old wells, known as ain, aiyûn, appear to be mostly of early Egyptian and Roman construction, and number over 400; exactly similar wells have been sunk by boring plant during the last few decades and are called bîr, biyâr; there are over 160 of these; all are true artesian wells. At the present day the method in vogue is as follows:—a two metre square timbered shaft is sunk by hand to the base of the red clay and within this is built up a watertight wooden pipe, 35 cm. in diameter, made of ‘sunt’ (a species of thorny acacia), the surrounding space being packed with clay. Sinking is continued in the sandstone with the boring machine until a satisfactory flow of water is obtained. Many of the older wells in the oasis have become choked up, and although some have been successfully cleaned out by the inhabitants, but the process is costly and laborious and frequently fails. The work is done by divers, a small but hardy class only found in Dakhla and Farafra.
The output of wells is determined in a somewhat rough and ready manner by measuring the depth of water passing over a weir fixed in the stream. It is reckoned in qirats, one qirat being a water-section of 64 square centimetres; from some test observations in Kharga Dr. Ball deduced the average value of a qirat, as measured in that oasis, as 230 litres a minute. The total water-output in Dakhla (1096 qirats) may thus be taken as approximately representing a discharge of 132 million cubic metres per annum, and taking the cultivated lands as 25,500 acres the duty is 6,130 acres per cubic metre per second. That the water-supply could be largely increased, and the limits of cultivation greatly extended, admit of no doubt, but with the free hand accorded the natives during the last few decades a considerable amount of damage has been done throughout the oasis by the injudicious sinking of wells. Promiscuous boring is fatal, and strict and efficient control of all boring operations imperative. Considering the number of wells abandoned owing to a slight fall in the water-level having caused them to cease running at the surface, the importance of lifting appliances, in the shape of shadûfs, saqias, or windmills, is evident, but until a few years ago the oasis was destitute of such appliances; a number of saqias have recently been fixed in the village of Mushîa and have met with success, but it is not an easy matter to persuade the inhabitants to have recourse to lifting appliances of any description.
Some of the Dakhla wells are of considerable depth; Bir-el-Dinaria, the most northerly in the oasis, is 144 metres deep and its water emerges with a temperature of 39·5° C. The best wells yield 9 or 10 qirats, though before the modern boring operations the output of some was as much as 16. The terms ‘artesian’ and ‘thermal’ may fairly be applied to the Dakhla wells, and it is noteworthy that the temperatures as a whole increase from south to north. The thermal character of the springs may be considered to be due to the great depths from which the water is derived, the actual temperature at the point of exit being dependent on local conditions, such as the depth of the well and the rate at which the water finds its way to the surface. It is probable that the water-bearing table has its outcrop in the rainy regions of Darfur, although some of its water may be derived by direct infiltration from the Nile in its upper reaches.
PLATE XXI.
THE EGYPTIAN OASES
Scale 1 : 6.000.000
