Wadi Abu Hireiq, draining the mountains of the same name, originates about latitude 22° 27′. On leaving the high mountains its channel divides, part of the drainage going north-east as Wadi Merdiyeb, and part south-east as Wadi Abu Hireiq. This latter wadi passes between the main mountains and a high isolated range of hills for about seven kilometres, then curves round to the eastward to join Wadi Hasium. There are numerous loopings and branchings of the wadis in this neighbourhood, caused by the feeders from the hills and by the presence of isolated hill masses, which the drainage lines frequently encircle, and it becomes impossible to say which of the various channels is the main wadi, so that the name Wadi Abu Hireiq is applied to all of them collectively.
Wadi Odruk is a small wadi draining between two groups of high hills south-west of Gebel Um Rasein; it joins one of the channels of Wadi Abu Hireiq about four kilometres above its junction with Hasium.
Wadi Nilateib, another small wadi further north, drains the south end of Gebel Um Rasein and the north-east faces of the hills close south-west of it. Coursing at first south-east for about three kilometres, it then curves round the foot of Gebel Um Rasein to join Wadi Hasium by two channels. There is a clear passage from the heads of both Wadi Odruk and Wadi Nilateib into Wadi Merdiyeb. All the wadis hereabouts contain plenty of trees and scrub, especially in their upper parts; as Wadi Hasium is approached they become more sandy and barren. It is, of course, the presence of vegetation available for grazing which determines the possession of a name by such small wadis as these two.
The drainage from the east face of Gebel Um Rasein joins Wadi Hasium directly by many small channels, which appear not to bear any special name.
Wadi Medarai, which forms the Wadi Ibib by its junction with Hasium, ten kilometres due east of Gebel Um Rasein, has its main head in Gebel Medarai, its length along its main channel being about twenty-five kilometres. By numerous tributaries, many of which contain abundance of trees and scrub, it drains the whole of the high hill country between Gebel Medarai and Gebel Um Rasein, and it also takes a part of the drainage from Kwat Hewah. One of its heads is said to lead to a rather difficult pass, south of Gebel Medarai, into the Wadi Kirwau, a tributary of Feqoh. For the first ten kilometres or so of its length, Wadi Medarai courses a little north of east; it then receives the feeder from Kwat Hewah above referred to, and changes its direction to a little south of east, passing close north of Gebel Um Rasein on its way to join Wadi Hasium on the sandy plain of the numerous feeders of Wadi Medarai from the hills west and north of Um Rasein, the principal is Wadi Merdiyeb, which originates ten kilometres south-west of Gebel Um Rasein by the splitting of Wadi Abu Hireiq. From this point of origin, it runs in a north-easterly direction in a rather sinuous course among the hills for about twelve or thirteen kilometres, joining Wadi Medarai close north of Gebel Um Rasein. Another little feeder of Wadi Medarai, though only about two kilometres long, is of some importance from its leading to Bir Um Rasein, a small well among the north foot-hills of Gebel Um Rasein.
Vegetation ceases to be abundant both in Wadi Medarai and in Wadi Hasium before their junction to form Wadi Ibib, and Wadi Ibib itself is for the most part a barren sandy ill-defined channel coursing north-eastward across a dreary plain for some fifty-seven kilometres to Mersa Shab. In this fifty-seven kilometres its fall is very nearly 300 metres, giving an average slope of only a little over five metres per kilometre. The slope of the lower part of Wadi Hasium is rather steeper than this, while that of Wadi Medarai is about twice as great.
But though Wadi Ibib itself is barren, it has some great tributaries which contains abundance of trees and scrub in their upper reaches, as well as several wells. The principal of these tributaries are the Wadis Soaorib and Um Bishtit, which with their feeders drain the mountains of Soaorib, Qidmib, Orgem, and Um Bishtit, while other smaller tributaries drain the lower hills north-east of Um Bishtit and Gebel Hamra Dom.
Wadi Soaorib originates in the midst of high mountains a little south of latitude 22° 10′, between the southern portion of Gebel Soaorib and the range which extends southwards from Hadal Aweib Meisah. At its head is a difficult pass westward into the head of Miti Kwan, a tributary of Alaqi. Curving at first eastward, it soon takes on a north-westerly direction, and in latitude 22° 11′ 30″ reaches a small open space called Mitba; here it is met by several tributary wadis of which the principal is the Wadi Haiyo, draining the eastern slopes of Gebel Soaorib. From Mitba the direction of Wadi Soaorib becomes more northerly, and about nine kilometres below Mitba it turns to the west, emerging from the mountains into the more open country which forms the south end of the great plain already referred to. Here it is joined by the Wadi Hankuk, draining north-eastward from Gebel Adar Qaqa, and a few kilometres further on by the Wadi Dishlo, which drains the western flanks of Hadal Aweib Meisah and enters Soaorib from the east. About three kilometres below the point of influx of Wadi Dishlo, Wadi Soaorib is joined from the south-west by another tributary which drains the west side of Gebel Um Seleim. From this point onwards, Wadi Soaorib courses a little east of north in a not very well defined course for about twenty-two kilometres over a gently falling sandy plain, joining Ibib to the north-west of the sand-swathed hills called Baqari Daba. In this part of its course, Wadi Soaorib receives small feeders from among the hills west of it on the plain, the principal of them draining north-eastward between the hills called Kulet Meiqrum and Kulet Tinasal. It also receives more important tributaries from the mountains to the east of it, the principal of these being the Wadis Eimya and Qidmib. Wadi Eimya drains the western face of Gebel Qidmib, while Wadi Qidmib drains the northern parts of the same mountain. Wadi Qidmib has two main heads; the western one lies between two high mountain ridges, and contains a well called Bir Qidmib, while the eastern one leads to a steep pass by which Wadi Meisah can be reached. Before reaching Wadi Soaorib, Wadi Qidmib is joined by other feeders draining the western flanks of Gebel Orgem and Baqari Daba.
From its head at the pass into Miti Kwan to its junction with Ibib, Wadi Soaorib has a length of about fifty kilometres. The level of the pass is unknown, but from Mitba to Ibib the level of the wadi floor falls from 505 metres above sea to 260 metres in a length of about forty-one kilometres, giving an average slope of six metres per kilometre. Most of the upper portions of Wadi Soaorib and its tributaries are well stocked with trees and bushes, but as the wadi crosses the sandy plain it becomes more and more barren. The place where it enters on the plain in latitude 22° 20′ marks a tribal boundary, the upper parts, including Wadi Dishlo, belonging to the Balgab Arabs, while the lower parts, including Wadis Eimya and Qidmib, are Kurbeilab territory.
Wadi Um Bishtit, which joins Wadi Ibib some five kilometres lower down its course than does Wadi Soaorib, heads in a small open space in latitude 22° 26′ and longitude 35° 35′. At its head there are two easy passes, one leading northward into the head of Wadi Habliai, another tributary of Wadi Ibib, and the other southward into the heads of Wadi Meisah. Just below its head Wadi Um Bishtit is joined by the small Wadi Delawet, draining the hills close to the south; while a little lower down is another small tributary from a rocky gorge among the south hills, which is important as leading to Bir Um Bishtit. This well, which was filled by downwash when I visited it in March 1908, is situated in the floor of the gorge at a sharp bend, about a kilometre up from the main wadi. According to the guides, it requires excavating about five metres deep, and yields water in quantity for about a year after rain, but when there has been no rain for a year only small supplies can be got, as it fills slowly; at the time of my visit there was no necessity to open the well because there was plenty of water in galts in the mountains of Meis-heit-ar, a little further south. The well is easy of access, and lies at 330 metres above sea-level.