From the mouth of Wadi Meneiga, Wadi Kreiga courses about 15° north of east, as a fairly wide wadi with a stony floor, with high hills on either side from which small feeders enter. The first large feeder, the Wadi Abiad, enters from the north-west, six kilometres below the mouth of Wadi Meneiga; it is a steeply falling wadi, which, like all wadis bearing the name of Abiad, has a floor of light-coloured granitic sand. Some eight kilometres lower down, two feeders enter from opposite sides: that from the north is called Wadi Eberer, while that from the south bears the name of Wadi Shigeg. Neither of these has been followed up far, and their length is unknown; but they are believed to be of no great extent. Below this point the country opens out considerably, and the wadi anastomoses round low hills, while its floor becomes less stony and more easy under foot. The various channels unite again about eight kilometres further down, where the wadi receives a tributary from the north-west just before it passes the high hill mass which forms the southward extension of Gebel Beida. This tributary leads to an easy pass, forming a direct road to Bir Beida. Lower down several lateral feeders come into Kreiga from either side, and the wadi emerges on to a sandy plain with scattered low hills. Across this plain Kreiga takes a more northerly direction for about sixteen kilometres to join the Wadi Hodein. The length of Wadi Kreiga from the mouth of Wadi Meneiga to Wadi Hodein is about fourty-one kilometres. Its fall between these points is from 405 metres to about 70 metres above sea-level, giving an average slope of eight metres per kilometre; the slope in the upper parts, where the wadi bed is stony, is of course somewhat greater, and that in its lower more sandy reaches is somewhat less than this average.
Wadi Kolaiqo is a very ill-defined drainage line heading in the low hills called Gebel Kolaiqo, and coursing north-east for about thirty kilometres across the sandy coast-plain to reach the sea about latitude 23° 0′. It is very sandy, and absolutely barren except for a little scrub in its upper parts. It would hardly have been noticed had not the triangulation station on the hill at its head been occupied.
Wadi Shab, with a basin of about 1,250 square kilometres, drains the eastern and southern portions of the great group of mountains of which Gebel Gerf is the centre, and reaches the sea in latitude 22° 52′, a little to the north of Mersa Shab. It has a great number of heads, most of which bear special names, the name Shab being applied collectively to them from the locality near the hill of Qrein Salama, about forty kilometres from the sea, where they begin to unite together into one great trunk channel. From the circumstance that its heads are situated in a high mountain mass where the rainfall is relatively great, and moreover have steeply falling stony beds which absorb but little of the precipitation, the upper portions of Shab and its feeders are well stocked with trees. Only in the last stages of its course to the sea, where the absorption of its drainage by the sandy coast plain becomes great, does the abundance of vegetation fall off and the channel become barren. Its principal heads and feeders are Wadi Radad (fed by Wadi Shellal el Sharqi), Wadi Tikosha, Wadi Muqur (fed by Wadi Ti Ilak), Wadi Qadiloi (fed by Tilat Tihu Shana), Wadi Baaneit, Wadi Kilanai, Wadi Um Saha, Wadi Diqdib, Wadi Sherefa el Sharqi, and Kwat Hewah. At least three of these contain good water sources, Bir Muqur, Bir Baaneit, and Bir Diqdib being situated in the upper parts of the wadis bearing the same names. The various heads and feeders of Shab will be described in detail below, commencing from the northernmost one.
Wadi Radad may be more properly described as a tributary than as one of the heads of Wadi Shab, as it joins the trunk wadi some fifteen kilometres below the other feeders. It originates in a rugged tract of high hills near Bir Meneiga, and courses eastward for about thirty-six kilometres, joining Wadi Shab on the coast-plain near the low hills of Ti Qireira, about twenty-four kilometres up from the point where Wadi Shab enters the sea. It has not been surveyed in detail, but its course was mapped from the triangulation station of Gebel Gerf and from other occupied stations whence portions of it were visible.
Wadi Shellal el Sharqi, a large feeder of Wadi Radad, originates in the mountains between Bir Diqdib and Bir Muqur. It has many heads, the best known of which is one coming from the west, leading to a pass into Wadi Shellal el Gharbi, a tributary of Wadi Madi; while another, a little further south, leads to another pass into Wadi Um Reddam and forms a possible road to Bir Sararat Seyet. Wadi Shellal el Sharqi follows generally a northward course, with a rapid fall, and joins Wadi Radad about eighteen kilometres below the head of the latter.
Wadi Muqur heads in the eastern mountains of the Gerf group, which are sometimes called Gebel Muqur. Here the drainage from several steeply falling rocky gullies collects into a single winding gorge shut in by the mountains. The limit to which camels can go up the gorge is marked by a well called Bir Muqur. At the time of my visit to this, in February 1908, the well was filled up by debris, through which, however, the water constantly rose and trickled into pools in a series of rock basins at slightly lower levels. The flow was at the rate of about five litres per minute, the overflow from the basins running to waste at this rate in the sand of the wadi. The water was of excellent quality. The Arabs state that when the water ceases to flow as a spring they dig out the debris and use the place as a well. Below the well, Wadi Muqur pursues a winding course north-eastward for about two and a half kilometres; then, receiving the short Wadi Ti Ilak, draining the mountains to the west, it turns sharply eastward and emerges from the high hills into lower country about three kilometres further on. In the lower country the wadi changes its direction to east-north-east, receiving many feeders from among the low hills west of Qrein Salama, and its bed divides and anastomoses into a series of channels, which eventually unite just before it enters Wadi Shab, five kilometres north-east of Qrein Salama. From near its head at Bir Muqur to its junction with Shab, Wadi Muqur has a length along its main channel of about nineteen kilometres; it falls from 470 metres above sea-level at the well to 200 metres at its junction with Shab, so that the average gradient is about fourteen metres per kilometre.
A few kilometres before reaching Wadi Shab, Wadi Muqur is joined by the Wadi Tikosha, draining the moderately high hills which lie between Wadi Radad and Gebel Muqur, and winding among low hills over the plain.
The Wadis Qadiloi and Baaneit drain from the east faces of Gebel Muqur and the mountains and hills close south and east of it, into Wadi Shab. There is an eastward extension of hills from Gebel Muqur, partly drained by Tilat Tihu Shana, which flows into Wadi Qadiloi; south of this extension there is a sort of bay, occupied by lower hills separating Wadi Qadiloi from Wadi Baaneit, through which several cross channels connect the two wadis. Bir Baaneit is a small well in Wadi Baaneit, near its head; it is said to yield water always, but refills slowly, so that only six to ten camels can be watered at once. A little below the well, Wadi Baaneit leaves the hills and courses north-east across a rapidly falling stony plain. On the plain, south of the main channel, are the two ruins called Darahib Baaneit. They are built of rubble stone set in plaster, with stucco facing in places, and appear to be ancient Moslem tombs, the larger one having evidently once supported a dome; there are about twenty Arab graves near the ruins.
South of Wadi Baaneit the plain is crossed by many drainage channels coursing north-east to join Wadi Shab, and the plain is covered here with quite a park-like growth of acacia trees. The principal channel, which comes from the hills about four kilometres south Bir Baaneit, is called Wadi Kilanai.
A little south of Wadi Kilanai the plain cuts far back to the west, and the drainage entering this portion comes from the heart of the Gerf mountains to the north-west. A large isolated granite hill-mass called Kilia Arib and numerous smaller hills break the monotony of the plain and cause much branching and looping of the drainage channels. The principal artery draining the south parts of Gebel Gerf is the Wadi Diqdib, which originates on the south flanks of the highest peaks, right in the heart of the mountain mass. In one of the heads is a well called Bir Diqdib, which, though of great service to the Koatil Arabs who inhabit this district with their camels and other animals, is of little importance to the traveller because of its situation in a closed-in wadi and thus not being on any route. From its head, Wadi Diqdib courses south-westward for fifteen kilometres or more among the mountains, receiving many feeders, before it emerges on to the plain. On leaving the mountains it splits up, part of its drainage going round by the north side of Kilia Arib, and part by the south, in each case by a number of anastomosing channels.