Megals are more likely to run dry than the larger springs, owing to their smaller collecting area. Any attempt to increase the flow of springs by blasting or excavation would probably only give an increase in yield at the expense of constancy; the throttling of the efflux is doubtless in many cases the chief reason for the perennial character of the yield of a spring, the rainfall being insufficient to maintain greater supplies than the springs yield at present.
Wells.
The wells of South-Eastern Egypt are mostly shallow excavations in the alluvia of the wadi floors, tapping the drainage waters which slowly percolate underground Nilewards and seawards from the mountain ranges. They are naturally more frequent in the districts near to the mountain ranges than in the lower reaches of the wadis, and the best wells are usually in well-defined trunk wadis which collect the drainage from myriads of smaller valleys. The wells sunk in the wadis at points remote from the mountain ranges are of immense importance to travellers crossing from the Nile, forming as they do the only supplies in an otherwise waterless journey of several days.
On an average, water is reached at a depth of eight to ten metres; occasionally, where the wadi is crossed underground by a rocky bar, the natural damming enables water to be reached at very shallow depths. The shafts dug by the Arabs are generally wide and very crooked, in order to permit of a man descending to fill a water-skin. Usually a “well” consists of three or four such shafts sunk in proximity. Occasionally, especially in the Bisharin country, the shafts are lined with rubble masonry, and rough timbers may be stretched across the mouth to facilitate hoisting by ropes. There is never any hoisting gear except at mines; rope is too much prized by the Arabs for it to be possible to leave ropes unguarded at a well, so each caravan uses its own rope and skins. Occasionally, the shaft is so cranked that the water cannot be seen from above. The reason for this is chiefly laziness in excavation; it is easier to deepen a well by driving out laterally a short distance and then sinking a narrow pit, throwing out the excavated material into the larger main shaft, than to hoist all to the surface. Near the wells one usually finds hods, or mud basins, into which the Arabs pour the hoisted water for their animals to drink. Frequently there are high hods for camels and low ones for sheep and goats.
After every considerable rainfall the wells become filled up with stony downwash, and have to be dug out afresh. There is no protective wall to prevent infilling; and, contrary to what might at first be thought, it is not laziness which conditions this circumstance. To the Arab, wells are a last resource. After rain, all the galts (rock basins) are full of good water. The Arab knows that the supplies in these galts will evaporate, while those in the wells, covered in by alluvium, are safe from loss by this cause. He therefore draws his supplies from galts as long as he can, and only when these are empty does he open the wells. The main wells never fail except after unusually prolonged drought, and then the condition of the Arab is sore indeed. The Bisharin do not drink much water, preferring to nourish themselves on the milk of their flocks and herds; but in times of drought the milk supply falls off because there is not sufficient moist vegetation for the animals to feed on.
The quality of water from the wells varies enormously with their situation and at different times. When water is abundant, it is generally good; but as the supply falls off and the wells have to be deepened, the slow infiltration carries abundance of sodium, calcium, and magnesium salts from the rocks, and the water is then often very unpleasant. The following analyses by Mr. Lucas of water-samples from some of the wells in 1906 will give a good general idea of the salts present; the figures give milligrammes per litre (parts per million):—
| Sikait Well. | Bir Masur. | Bir Metawit. | Bir Abu Hamamid. | Bir Shadli[115] | Bir Helie. | ||
|---|---|---|---|---|---|---|---|
| I. | II. | ||||||
| Total solid matter in solution | 7,360 | 880 | 4,020 | 1,720 | 2,380 | 2,980 | 4,040 |
| Cl | 1,263 | 57 | 1,027 | 225 | 555 | 749 | 323 |
| SO3 | 2,530 | 263 | 1,042 | 318 | 540 | 776 | 1,447 |
| CaO | [116] | 200 | 350 | 330 | 310 | [116] | 610 |
| MgO | [116] | 29 | 116 | 87 | 69 | [116] | 211 |
| Equivalent of Cl as NaCl | 2,075 | 94 | 1,687 | 370 | 912 | 1,231 | 530 |
| Equivalent of SO3 asNa2SO4 | 1,850 | 1,377 | 466 | 550 | 960 | 1,377 | 2,569 |
| Alkalinity to methyl orange calculated asNaHCO3 | 500 | 222 | 550 | 848 | 298 | 260 | 651 |
All the above waters were quite drinkable, though that of the Sikait well was rather disagreably salty.
An analysis of the water of one of the Halaib wells in 1895 is given by Dr. Natterer,[117] who found (in parts per million):—
| Cl | 336 |
| SO4 | 449 |
| CO3 | 48 |