The 'Sadd' of the Upper Nile: its Botany compared with that of similar Obstruc- tions in Bengal and American waters. BY C. W. HOPE. INTRODUCTORY. HE Cataracts on the Nile are well-known obstacles to T navigation between its mouth and the Soudan, but they are beginning to yield to the attacks of modern engineers, who are throwing dams across the river, and providing side channels through which navigation will be carried on by means of locks. These cataracts are caused by barriers of granite rock which cross the bed of the river. But it is not so well known that an almost more serious obstruction to navigation is caused by the accumulation of a few species of plants floating in the Bahr-al-Jebel, or Mountain Nile, beginning about 435 miles south of Khartum, and extending thence .southwards for about 350 miles; and that this accumulation also seriously reduces the flow of water north- wards to the Lower Soudan and Egypt. The great Equatorial Lakes store the rainfall of vast catchment basins, and so regulate its off-flow northwards by means of the Mountain Nile ; but this function is greatly neutralized by the vegetable accumulation which begins 715 miles northward, in a com- paratively flat country, and which reduces the velocity of the current, and also causes the water of the river to spill right and left over the country and go to waste in shallow lakes and lagoons, where it is subject to evaporation to a serious extent. [Annul, of Botany, Vol. XVI. No. LXJ1I. September, igog.] Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 496 Hope.—The 'Sadd' of the Upper Nile. Previous to 1863 both the Bahr-al-Jebel, or Kir, and its eastern branch, the Bahr-al-Zaraf, had been navigable, but in March of that year the Nile, below their junction with the waters coming in from the west and northward—thence northwards called the White Nile, or Bahr-al-Abiad—was found to be blocked by ' an accumulation of vegetable flotsam, and it cost the crew of the Tinne" Expedition two days' hard labour to take their vessel through a channel which had been partially cleared by their predecessors. The obstruction rapidly increased, and thirty vessels had to be employed for five weeks to open a permanent passage. Matters went from bad to worse, till, in 1874, Ismael Ayub Pasha cleared the main route by the White Nile and the Kir. But in 1878 ' the White Nile rose to an unusual height, and enormous quantities of vegetable debris were carried off by the current. A formation of bars (blocks) on an unprecedented scale was the result, and communication between the Upper and Lower Nile was not restored until 1880.' If the Kir and the White Nile, with their comparatively strong current, were thu9 obstructed, it was natural that the more sluggish Bahr-al- Ghazal should contain more extensive though less compact accumulations. ' In 1881 Gessi Pasha spent three and a half months on a part of the voyage westward usually performed in five hours, and lost half of his men by starvation. Between the mouths of the Kir and the Bahr-al-'Arab there were twenty distinct dams.' The above information has been found in the' Encyclopaedia Britannica'; but—fully to realize what the Nile'Sadd'is—it i3 necessary to read the Report by Sir William Garstin, K.C.M.G., as to Irrigation projects on the Upper Nile, &c, accompanying a despatch by Lord Cromer, His Majesty's Agent and Consul General at Cairo, which was published as a Blue Book in July, 1901. In Part II of his Report, 'Points for future Study,' we find a section ' The Sudd.' (The spelling of this word is various in these papers, and the pronunciation consequently uncertain; but it seems probable that ' Sudd' is a transliteration into English, and that the word ought to Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 Hopt—TJu 'Sadd' of the Upper Nile. • 497 be pronounced like the first syllable of ' sudden,' and there- fore, to all but Britons, ' Sadd' would be the better guide.) Sir William Garstin says that his Report is the result of his observations made during three consecutive years. In 1900 he had ' the advantage of studying the actual process of its formation on the spot,' as he. was imprisoned for three days in the Gebel River, owing to the ' Sudd having burst in ' (from the side lakes and lagoons) ' and blocked the channel down- stream of the steamer.' ' In 1890—91 a reconnaissance survey of the Bahr-al-Gebel (or Jebel) from Lake No southwards to Gondokoro was finished ; and a map to the scale of 1 inch to 10 kilometres is given with Sir William Garstin's report: it shows very clearly the features of the river's course; the lakes and lagoons met with ; the positions of the ' Sadd ' blocks then found, and the nature of the swamps, whether papyrus or grass. The last block met with, the nineteenth, was just above the 400 kilo- metres point from Lake No, near Ghaba Shamb^, one of the Nile Posts of the Bahr-al-Ghazal Province. Papyrus swamps ceased at about'460 kilometres, and the plant does not seem to have been found south of about 520 kilometres. ' In the Bahr-al-Jebel,' says Sir William Garstin,' the main factors of the " Sadd " are—the papyrus, and the " um-soof" (or omm-soof) reeds. These two, with the earth adhering to their roots, form the real obstacle. Many of the smaller swimming plants, such as the Azolla, the Utricularia, and Ottelia, are mingled with the others; but they certainly do not play any important part in the formation of the obstacle. The ambatch, too, has been unjustly accused of assisting in forming the barrier. This is not the case. This plant does not grow in any great quantity in the vicinity of the Bahr-al- " Gebel, and its stem is so light and brittle that it would break when subjected to great pressure. ' On the Bahr-al-Ghazal, on the contrary, the sudd is chiefly composed of the swimming plants above mentioned. Their breeding places are Lake Ambadi and the other lakes to the south. The Ghazal sudd is much lighter in texture than that Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 498 Hope.— TIie 'Sadd' of the Upper Nile. of the Gebel, and is consequently much easier to remove. At the same time, even in the former river the sudd is at times dangerous, especially if it forms down-stream of a vessel, and if the latter has to work upon it from its up-stream end. The accident to Gessi Pasha's expedition in 1881 proves that even the Bahr-al-Ghazal sudd can be an impassable obstacle under such circumstances.' How these various plants come to be so massed, in the respective rivers, as to form the barrier called ' Sadd,' or ' Sudd,' is very graphically explained by Sir William Garstin ; but the account will not bear abridgement, and it must be read in the Report itself. THE BOTANY OF THE ' SADD.' The mention, in Sir William Garstin's Report, of certain plants, as inhabitants of the swamps and lagoons of the Upper Nile and its branch the Giraffe Nile, and its tributary the Gazelle Nile, and as constitutional parts of the ' Sadd,' has led to an investigation of these plants from a botanical point of view, and the following are the identifications which have been made, and notes as to their characteristics. The Papyrus Plant. The Papyrus plant—Cyperus Papyrus, Linn.—was, in ancient times, widely cultivated in the Egyptian Delta, where it was used for various purposes, but especially in making a writing material; but it is now extinct in Lower Egypt, and it is believed that it was not indigenous there, but probably had been introduced from Nubia. A clump of it grows in the tank- house in the Royal Botanic Gardens, Kew, with many stems, some of which are 9-10 feet in height above the water, while others, also in flower, are only about 6 feet high. A very characteristic picture of a large clump, backed by a tall grass or reed, is to be found in the Gardeners' Chronicle for 1870, p. 314, which was taken from a photograph of the plant as it grew on the Anapo River in Sicily. The plant has been re- cently and authoritatively dealt with by Mr. C. B. Clarke, F.R. S., Downloaded from https://academic.oup.com/aob/article-abstract/os-16/3/495/206486 by University of California, Santa Barbara user on 16 March 2018 Hope.—The 'Sadd' of tlte Upper Nile. 499 in the ' Flora of Tropical Africa,' Part II, vol. viii. Mr. Clarke gives Cyperus Papyrus, described by Linnaeus in his ' Species Plantarum,' as the typical species, and names Cyperus syriacus of Parlatore (which grows on the Jordan) and Papyrus sicula, Parl., and P. antiquorum, Link, as synonyms; and he separates, but only as a variety, P. antiquorum, C. B. Clarke. He gives the habitats of the typical plant as Africa : Upper Guinea, Lower Guinea, South Central Africa, and the Mozambique District; and the habitats of his variety as, in Asia—Palestine; and in Africa—Nile Land, the White and Gazelle Niles, Mozambique, and Zanzibar.