=Wadi Alaqi=, the greatest of all the Egyptian wadis draining westwards to the Nile, has its head on the main watershed near Gebel Is, close to the 22nd parallel in longitude 35° 27′. Its main channel, over 350 kilometres in length, pursues a general westerly course, winding at first, past the old mining centres of Darahib and Alfawi, towards Gebel Muqsim, on the 34th meridian, and then, curving round to the north of that mountain, it turns to the north-west, past the gold mines of Um Gariart, and enters the Nile Valley opposite the large village of Dakka, in latitude 23° 8′. The area of its basin is unknown, much of it being unexplored, but it probably comprises no less than four square degrees of the earth’s surface, or 44,000 square kilometres. Its heads and upper tributaries lie among high mountainous tracts partly in Egypt and partly in the Sudan, and occasionally the rainfall in these southern parts of the eastern desert is sufficient to convert the usually dry wadi into a temporary stream for a part or all of its length. That it may on the rare occasions of sufficient rainfall discharge no inconsiderable quantity of water into the Nile is proved by Linant’s experience about 1830, when he records that the torrent from the Wadi Alaqi into the Nile was so great as to prevent his _dahabîa_ sailing up the river past the point of influx, even with a good wind and all sails set.[87] A great flow of water down the Wadi Alaqi also occurred in the autumn of 1902 as a consequence of heavy rains in the mountainous country east of the meridian 34° 30′. This torrent was observed by Mr. John F. Wells, who was then manager of the Um Gariart mine. In the early morning news was brought to the mine that great waters were coming down the wadi. Except for a slight rainfall at the heads of the Wadis Qoleib and Haimur, the drainage of which did not appreciably swell the flood of the main wadi, there had been no rain within one hundred kilometres of the mine, and when the alarm was given, at 6.30 a.m., only a small trickling of water down the wadi was visible, and the news was thought to be an exaggeration. But an hour later the whole wadi was a raging torrent, and by nine o’clock there was a mighty stream, over 300 metres wide and from one to two and a half metres deep, rushing past the mine. The flow continued for about two and a half days. On this occasion the stream, in spite of its magnitude at Um Gariart, did not reach the Nile; after flowing for some seventy kilometres past the mines, it entered a wide depression at Hagab Kara, some forty kilometres from the mouth of the wadi, where it formed a great pool and sank into the sand. Mr. Wells informs me that the water did not penetrate the sandy and gravelly floor of the wadi to the bed rock (the thickness of the sandy and gravelly layer at Um Gariart is fourteen metres) till three months later, and then the rock, though damp, did not absorb enough water to yield any supply to wells sunk in it.