Wadi Beds Research Articles

Infiltration-recharge through wadi beds in arid regions

Abstract Groundwater recharge in arid regions is intermittent and usually occurs as a result of flood flow transmission losses in dry wadi channels. Hydrograph characteristics play a dominant role in determining the amount of channel abstraction in relation to the width of the wetted perimeter and the time of inundation, and the subsequent groundwater recharge. Large variations in the magnitude of channel losses result mainly from the diversity in inflow volumes. The magnitude of groundwater recharge in relation to bed transmission losses is dependent on flood volume and duration, soil moisture content and physical soil profile characteristics. Runoff volume and duration are the dominant factors influencing the cumulative infiltrated volume and recharge to shallow water tables. Taking into consideration the influence of various hydrological and channel characteristics, several regression equations are suggested to estimate the transmission losses from a wadi bed and the groundwater recharge.

The role of light and water in the establishment of mullein (Verbascum sinaiticum and V. fruticulosum) in a gravel wadi bed

Two mullein species Verbascum sinaiticum Benth. and Verbascum fruticulosum Post became established side by side in an erratically flooded gravel bed of the Zin basin in the Negev Highlands. In the laboratory, mass and uniform germinating V. sinaiticum seed lots enhanced the germination of less alert seeds from the same or closely related species if the seeds were germinated in clusters in the same petri-dish. Such a ‘population effect’ appears to be a novel phenomenon in seed biology. Potassium nitrate (50–100 mM) delays and inhibits germinability in light-requiring seeds, probably due to a gradual change in osmolarity. The causal event described in this study results in a unique niche which enables the establishment of distinctly different biennial and perennial mullein species.

Distribution behaviour of common plant species along physiographic gradients in two wadi beds of Southern Sinai

This study is an analysis of the relationships between the distribution of common plant species in the beds of Wadi El-Sheikh and Wadi Saal near Saint Katherina area in southern Sinai, and variations in altitude, gravel percentage and soil texture. The absolute density of eight perennials and the presence of nine annuals were estimated in 86 stands using 100, 2 m × 2 m quadrats in each. Altitude and the percentages of gravel, sand, silt and clay were determined in each stand. The perennials were more sensitive than annuals to variations in these physiographic factors. The notable changes in the abundance of perennials along their gradients indicated that the vegetation in the study area can be characterized into discrete units. The distribution of perennials was more related to altitude and the percentage of gravel rather than to the percentages of sand, silt and clay.

الاستعاضة الاصطناعية للمياه الجوفية من رسوبيات الأودية

A series of field experiments and theoretical analyses of different infiltration-recharge processes in the alluvial system are presented. Theoretical analysis of one-dimensional vertical infiltration, lateral recharge, and recharge through the unsaturated wetting front were carried out. Field studies indicate that the soil heterogeneity and flood hydrograph characteristics have a prominent influence on the amount and duration of recharge. Infiltration-recharge equations for a clogged surface layer condition seem to be the best suited for estimation of recharge in most wadis in the Kingdom. In addition, it was shown that the infiltration-recharge process can be enhanced (35%) through artificial recharge schemes involving the construction of a series of inflatable-deflatable rubber dams across the wadi bed for the conditions in wadi Tabalah. These dams may be used to increased the duration and contact area of runoff and may result in a significant increase in the amount of recharge.

Recent Rainfall Changes and Their Impact on Hydrology and Water Supply in the Semi- Arid Zone of the Sudan

1980s, with 1984 the driest year on record and all annual rainfalls from 1980 to 1987 well below the long-term mean. In White Nile Province annual rainfall in 1965-84 was 40 per cent below 1920-39 levels; wet season length has contracted by 39-51 per cent; and the frequencies of both large and minor daily rainfalls have declined by up to 51 per cent. Hydrological consequences in North West White Nile have included reduced frequencies of wadi flows and overland flow; a major decline in shallow aquifer recharge and perched water-table levels in wadi bed and inselberg front locations (but little effect on deep regional aquifer levels); and earlier exhaustion in the dry season of shallow wells, surface pools and reservoirs. The significant decline in large rainstorm frequency has outweighed any tendency of land degradation (via reductions in infiltration capacity due to overgrazing, mechanized agriculture and deforestation) to enhance run-off levels. In some other parts ofthe Sudan, however, the reverse is true. In order to be useful, models of the hydrological impact of rainfall decline must take into account local physical and human conditions, changes in a range of rainfall parameters, and different types of human response to drought.

Nitrogen in a wadi ecosystem, Fezzan, Libya

Total ammonium nitrogen contents for three desert grasses, Panicum turgidum, Pennisetum divisum and Stipagrostis scoparia, and for a leguminous shrub, Retama retam, are reported together with determinations of the extractable nitrate and ammonium nitrogen, the cation exchange capacity and the total and inorganic carbon contents of the wadi bed alluvium in which they grow. The determinations are for plants from the Fezzan, Central Sahara. Comments are made on the nitrogen cycle for this desert site. We believe that these are the first data of their kind for the Central Sahara.

Compliance of a biennial mullein (Verbascum sinaiticum Benth.) to erratic desert floods in the Negev highlands, Israel

Wadis of the Negev desert highlands are characterised by irregular flash floods and, consequently, their beds typically comprise coarse gravel. The biennial Verbascum sinaiticum Benth. tends to establish temporary stands on such wadi gravel beds, and these exhibit a contagious pattern of distribution. V. sinaiticum, which is native to the Afro-montane region, acquires a fugitive character in the Negev. Its seeds germinate mainly on the third or fourth days after wetting. Optimal germination was obtained in continuous light at 25°C; a gradual increase in Nacl, up to 80 m M caused a delay in germination and reduced the daily rate. Irregular fluctuation of the water regime and the unstable nature of the wadi beds are essential for the establishment of V. sinaiticum. Flash floods are also necessary for its existence: they provide periodic reformation of the disturbed habitat, removal of potential competitors, dispersion of the seeds of V. sinaiticum and wash-out of excess salts. Another mullein, V. fruticulosum Post, a perennial herb, occupies the shoulders of the same wadis, as well as the terraces above them. Its distribution is sparse and the pattern tends to be random. The rôle of floods in the allopatric distribution of the two species of Verbascum is discussed.

Jebel Tageru. A contribution to the flora of the southern Libyan Desert

During an archaeological field campaign in Northern Sudan a survey to Jebel Tageru was undertaken. Situated on the southern edge of the Libyan desert, the mountain plateau seems to offer favourable conditions for plant growth. A description of the survey and the vegetation types of different habitats, e.g. the wadi beds, the alluvial plain and the sand dunes, is given. An annotated list is appended. It contains the names of 38 plant species collected during the survey, most of which belong to the floristic category of the Saharo-Sindian Region.

Sudanian Elements in the Flora of Israel

In the Dead Sea Rift Valley of Israel, a northern tongue of penetration of Sudanian elements exists that has traditionally been regarded as composed of Miocene relicts. We postulate that most of these elements have penetrated the area since the end of the Pleistocene. The principal habitats harboring Sudanian elements in Israel are described, including the pseudo-savanna in wadi beds, cliffs and rock formation, oases and in the Dead Sea Rift as well as a variety of secondary habitats outside the Rift. In addition, a statistical analysis of the 116 species in the flora of Israel considered to be Sudanian elements is presented, covering growth form, phytogeographic distribution, dispersal mechanisms, and degree of endemism. Special attention is given to the arboreal elements, including 49 species of trees, shrubs, and perennial vines. A comparison is made between the habitats of these species in East Africa and in Israel: significant habitat shifts were found in some cases. Although paleo-macrofossils are almost non-existent in the area, other evidence, such as low degree of endemism, disjunctiveness, and adaptations to aridity and long-distance dispersal indicate that the great majority of the Sudanian elements in the Dead Sea Rift are of recent origin. The relationships between the typical evergreen Mediterranean elements with paleotropical origins and the extant Sudanian elements in Israel are discussed. Within the portion of the Syrian-African Rift lying between the Red Sea to the south and the watershed of the Jordan River in the Golan Heights, a large number of Sudanian elements, plants as well as animals, are found considerably farther north than anywhere else in their distribution range and in many cases growing under ecological conditions quite different from their norm. In addition, a handful of Sudanian species also occur in the low-lying coastal plain of Israel, almost entirely cut off from the Dead Sea Rift Valley and the bulk of the Sudanian region proper (Fig. 1). Climatic and geological conditions in the Dead Sea Rift Valley explain in part the presI A. Shmida wishes to express his considerable debt of gratitude to the late Prof. M. Zohary who introduced him (and dozens of other students) to the intricacies and unique attributes of the Israeli flora. We thank G. E. Wickens who reviewed the manuscript with meticulous care, helped gather information for some of the distribution maps, and made valuable suggestions for improvement of the text. J. B. Gillett and P. Quezel also kindly reviewed the manuscript and provided stimulating comments and suggestions. Our thanks also go to Sandy Greenberg, Seemah Shemesh, and Marion Milner who provided computer and typing assistance, to Nancy R. Morin and Dr. Marjorie Tiefert for patient and professional editorial guidance, and to Miri Shmida who drew the figures. The assistance of J. Dransfield in preparing Figure 5 is gratefully acknowledged. Any errors or inaccuracies therein are entirely the responsibility of the authors. Finally we thank the numerous guides of the Israeli Society for the Protection of Nature who helped us locate some of the rare and little-known populations of Sudanian plants in Israel. We gratefully acknowledge financial assistance received during the course of this research from the Bath-sheva de Rothschild Fund to A. Shmida and the Clifford M. Hardin Fund of the Fund for Higher Education to J. A. Aronson. 2 Department of Botany, The Hebrew University of Jerusalem, Jerusalem, Israel. 3Rudolf and Rhoda Boyko Institute for Agriculture and Applied Biology, Institutes for Applied Research, Ben-Gurion University of the Negev, P.O. Box 1025, Beer-Sheva 84110, Israel. ANN. MissouRi BOT. GARD. 73: 1-28. 1986. This content downloaded from 157.55.39.253 on Sat, 11 Jun 2016 07:14:14 UTC All use subject to http://about.jstor.org/terms 2 ANNALS OF THE MISSOURI BOTANICAL GARDEN [VOL. 73

Development of sustained land use by understanding soil and landscape formation in the desert fringe area of NW-Egypt

A soil survey was carried out in a small area on the mediterranean coast in north-west Egypt, 20 km east of Marsa Matrouh. The objective was to give a scientific contribution to land use planning in the coastal zone. Between plateaus and depressions the following soil units have been found (description according to the FAO-classification): a Calcic Yermosol (petrocalcic, saline and sodic phase), a Calcic Yermosol with exposed calcrete, a Haplic Yermosol and a Luvic Yermosol (sodic phase). In wadi beds Calcaric Fluvisols and on wadi banks Calcaric Regosols were determined. Analysed as characteristic soils were a Calcic, a Haplic and a Luvic Yermosol. From analysis and field observations site qualities were derived. In all profiles and depths the soils have high pH values, a moderate salt content and a high calcium carbonate content. The nutrient supply is neither a limiting nor a differing factor. Rooting depth, water capacity and position are important site qualities. They were compared with the demands of potential crops for the area (olives, figs, date palms, barley, water melons, alfalfa). So suitable areas for the crops were found. The deep Luvic Yermosol fit for all crops, the extremely shallow Calcic Yermosol (petrocalcic phase) is unsuitable for all crops. Measures for the improvement of rainfed agriculture are recommended.

Development of sustained land use by understanding soil and landscape formation in the desert fringe area of nw-Egypt

A soil survey was carried out in a small area on the mediterranean coast in north-west Egypt, 20 km east of Marsa Matrouh. The objective was to give a scientific contribution to land use planning in the coastal zone. Between plateaus and depressions the following soil units have been found (description according to the FAO-classification): a Calcic Yermosol (petrocalcic, saline and sodic phase), a Calcic Yermosol with exposed calcrete, a Haplic Yermosol and a Luvic Yermosol (sodic phase). In wadi beds Calcaric Fluvisols and on wadi banks Calcaric Regosols were determined. Analysed as characteristic soils were a Calcic, a Haplic and a Luvic Yermosol. From analysis and field observations site qualities were derived. In all profiles and depths the soils have high pH values, a moderate salt content and a high calcium carbonate content. The nutrient supply is neither a limiting nor a differing factor. Rooting depth, water capacity and position are important site qualities. They were compared with the demands of potential crops for the area (olives, figs, date palms, barley, water melons, alfalfa). So suitable areas for the crops were found. The deep Luvic Yermosol fit for all crops, the extremely shallow Calcic Yermosol (petrocalcic phase) is unsuitable for all crops. Measures for the improvement of rainfed agriculture are recommended.

Evolution of reg soils in Southern Israel and Sinai

Reg soils (mostly Camborthids and Gypsiorthids) cover some 15% of the Negev and Sinai deserts. Analytical data of seven profiles on depositional surfaces of increasing age in the Negev show clear relationships between ages of surfaces and soil profile features, exemplified in the development of the cambic, salic and gypsic horizons.The youngest soil, a Coarse Desert Alluvium soil (Typic Torriorthent) of dry wadi beds, up to a few thousand years old, has little profile differentiation and is generally non-saline or slightly saline. On the higher terraces connected with the Lisan Formation (about 70 000–12 000 years B.P.) clear profile differentiation and the beginning of development of cambic horizons can be discerned, evident in their colour-textural p differences. The soils are already saline and somewhat gypsiferous. Both soils are not yet defined as Regs because of their negligible or restricted profile differentiation.Reg soils on the older and higher geomorphic surfaces in the Arava Rift Valley, several hundred thousand years old, have well-differentiated profiles, with cambic, salic and gypsic horizons. Below their stony desert pavements, typical Reg soils have light coloured vesicular horizons, over mellow, very pale brown loam, frequently with laminar structure, almost completely stone-free layers. The reddish brown loamy to clay loam B horizons are very saline and show intensive salt weathering of gravels. Gypsic and petrogypsic horizons occur at depth. Such Reg soils represent the stable surfaces and soils of deserts and were developed over a long period of desert weathering.

Groundwater flow systems in the arid crystalline province of Southern Sinai

ABSTRACT A hydrogeological research project was conducted in the arid crystalline province of the Southern Sinai. To gain a better understanding of regional groundwater flow patterns, Landsat images as well as air photos were used. Three main flow systems were investigated: (1) The flow system occurring along longitudinal regional crustal fractures with the direction parallel to the Gulf of Elat Rift; this system captures the flow in the main wadi beds draining eastwards. (2) The flow system found in shallow fractured rocks, capturing the flow in small tributaries in the upper part of the drainage basin. (3) The system of dikes governing the flow regime in wadi beds draining westwards. The preliminary estimate of the recharge into the fractured crystalline aquifers and the interconnected gravel bed aquifers is in the order of magnitude of 10–15% of the total precipitation.

Eco-physiological studies on desert plants X. Contribution to the autecology of the desert chasmophyte Stachys aegypticca Pers.

Stachys aegyptiaca Pers. is a desert calcicolous chasmophyte. Its growth in the Egyptian Desert is confined to the limestone formations of the Northern Arabian Desert, Sinai and the Isthmic Desert. The plant lives under harsh climatic conditions: high summer temperatures with mean maxima above 35°C and low rainfall ranging from 9.4 mm/annum at El-Tor to 87.3 mm/annum at Hemme.The vegetation dominated by Stachys aegyptiaca is a pioneer stage in the development of the wadi bed ecosystem. Other chasmophytes are the main associates of the Stachys community. The studied plant has been recorded among the associates of numerous plant communities.Runoff, accelerated by the rugged topography in areas where the plant grows, and the stoniness of the substratum contribute to securing ample water supply to the plant.The daily march of the transpiration rate was investigated in two seasons. It has been clear that there is an obvious regulation of transpiration in summer.The osmotic pressure of the plant sap was determined at regular monthly intervals throughout one year. The average osmotic value is 17 atm, ranging from 13.8 atm in April to 19.3 atm in November.

Natural Environment and Water Use

Yemen Arab Republic is located in the south-western corner of the Arabian Peninsula. The area lies between parallels of latitude 12°30' and 17°30'N. and meridians of longitude 42°30' and 46°30T. Yemen was known as “Arabia Felix” and had high civillization in ancient age. But since its hard natural environments, the development of this country fell behind the time. Among of them, water supply problem is the most important matter. In response to the request made by the Government of the Yemen Arab Republic, the preliminary survey of the “Rural Water Supply Projects were carried out by the Japan International Cooperation Agency (JICA). In this paper at first, we elucidate the background of water supply problems and the feature of geohydrological condition of this country. Next, we clarify the mode of occurrence and movement of groundwater which is restricted by the condition mentioned above.The summary of this paper is as follows : 1. Topographical feature.i. Yemen's main watershed runs from north to south and divides the country into two parts, western half and the eastern half.ii. The main watershed or central highland is comparatively flat and in some areas tectonic basins are pointed out.2. Hydrological feature.i. As shown in Figure 7, the highest annual rainfall falls in the central highlands and the lowest in the eastern lowlands and the western lowlands.ii. Springs are observed in the wadi beds and support some small streams in the mountain area.3. Hydrogeological feature.i. Geological succession is shown under.(lower to upper) Basement complex-Pre-CambrianWajid sandstone-OrdovicianKohlan series-Lower JurassicAmran series-Upper JurassicTawilah group and Medj-Zir series--Cretaceous to PaleoceneYemen volcanics-Upper Cretaceous to TertiaryBaid formation-Miocene to PlioceneQuaternary basalts-Alluvium ii. Main aquifer in this country is Alluvium, Quaternary basalts and Yemen volcanics. On the other hand the rest can be regarded as aquitard or aquiclude, (especially basement complex as aquifuge).iii. As shown in Figure 12, aquifers are exposed in the central highlands and in the eastern and the western lowlands and aquitards or aquicludes are exposed in the mountain area.4. Mode of occurrence and movement of groundwater.i. From mentioned above condition, the central highlands can be regarded as recharge area of groundwater.ii. For the most part, perennial streams in the mountain area are feeded by the outflow of groundwater from the central highlands.iii. In Tihama plain and the eastern lowlands alluvium underlies a thick cover of eolian deposits and for its high infiltration capacity, surface flow change into groundwater rapidly.

Competition between two desert varieties of Medicago laciniata (L.) Mill. under controlled conditions.

Two varieties of Medicago laciniata common in the Negev desert of Israel reveal a distinct pattern of distribution within two different plant communities: M. laciniata var. laciniata occupies northern slopes and wadi beds within the association of Artemisia herba-alba, and M. laciniata var. brachyacantha occupies more arid southern slopes within the Zygophylletum dumosi association. Recent field trials have shown that interaction within the plant community restricts distribution of the two varieties, particularly on the northorn slopes.Using the de Wit model on competition, an attempt was made to determine whether the distribution found in nature can be explained on the basis of competition for space. Intervariety competition was measured under controlled conditions in a phytotron under two water regimes. It was found that under both "wet" and "dry" conditions, the two varieties utilize the same space (RYT=1) and similar quantities of water, and both produce similar amounts of dry matter. According to the total dry matter, the varieties have about the same competitive ability under wet as well as under dry conditions.However, under the dry treatment the relative crowding coefficient, based on seed yield, is very different from one: k lb>2. The relative reproductive rate αlb < 1, found under both water regimes, indicates that var. brachyacantha will replace var. laciniata through competition for the same space. This is not in accordance with the observations that var. brachyacantha is absent in the less arid northern slope. A possible explanation is discussed.Reciprocal thinning of the one variety from various mixtures grown under the "dry" regime, when followed by irrigation to field capacity, sharply increases the consumption of water by the plants left, proportional to the number of plants removed. This does not occur in cultures grown under the "wet" regime. It is suggested that such competition for water under optimal water conditions may be due to the occurrence of associations of roots. The possible formation of root associations and its ecological significance of their effect on water consumption are discussed.

Allopatric Distribution of Two Varieties of Medicago Laciniata (L.) Mill. in the Negev Desert

Medicago laciniata (L.) Mill. is a winter annual represented in the Negev by two varieties: M. laciniata var. laciniata and M. laciniata var. brachyacantha Boiss. The first variety has larger pods with markedly longer spines (Fig. 1) and occurs in relatively less arid habitats (Heyn 1963). In the Negev, near Sede Boqer (300 52' 49 N, 340 51' 27 E), it occupies northern slopes and wadi beds dominated by the association of Artemisietum herbaealbae (Zohary 1962; Friedman 1969). The second variety occurs in more arid habitats, such as southern slopes and hill tops dominated by the association of Zygophylletum dumosi. Thus, the populations of the two varieties occupy distinct adjacent territories and meet along the base of the southern slopes where intermediate forms occur within a narrow strip (Fig. 2). Rodents and ruminants are common in the area and are capable of carrying the spiny pods tangled in their fur from one slope to another. Seeds are also dispersed by these animals through their faeces since a few at least remain viable after passing through the ruminant digestive system. Seed longevity of both varieties is considerable. Germination of 20-year-old seed was tested and was found to be 8500 after 48 h. The aim of the present study was to investigate the factors controlling the distribution of the two varieties. The growth, development and yield of each variety was evaluated under the relevant environmental conditions with and without the effect of the associated plant communities.

Recognoscering på den nordlige del af Oman halvøen. En foreløbig rapport

Recognoscering på den nordlige del af Oman halvøen. En foreløbig rapport

Phytogeographical Distribution in Egypt

In spite of a rich variety of natural conditions, the flora of Egypt is not very rich in the number of species; a considerable number of species is limited to certain territories only (Mediterranean, Sinai, Gebel Elba). Consequently, there are some 700 common species, meanwhile other species are rare or very rare. The total number of species makes about 2 000. Botanical life in Egypt is predominantly concentrated to the Cairo and Alexandria Universities. A leading personality is Prof. Dr. V. Täckholm, the author of the "Flora of Egypt", the co-foundress of the herbarium collections at the botanical library, and an outstanding pedagogue at the Cairo University who has educated a new generation of botanists in Egypt. A prevailing part of the Egyptian territory is covered by deserts with arid conditions. Phytogeographical distribution is mentioned in books by Muschler, Hassib, Täckholm. All these classifications are based upon the natural geographical reality. The Nile Valley is considered a single whole yet it is evident at first sight that its northern part differs greatly from the southern one, both in quantitative and qualitative presence of species. These problems are at the present the subject of studies of Egyptian botanists. Similar natural conditions occur in the Nile delta where there are vast areas of saline soils and shore communities of brackish lakes. From the botanical point of view the most interesting phenomenon is the weed vegetation which serves as basis for a more detailed phytogeographical distribution of the Nile Valley, and differentiation of the delta from the valley itself. The coast of the Mediterranean is divided into two parts: the east pelusitic part, affected strongly by the vegetation of the eastern Mediterranean, and the west mareotic part displaying a relationship to the coastal vegetation of North Africa. Thanks to a rich rainfall, the Mediterranean is one of the territories in Egypt which display the richest variety of species. The Libyan desert, situated to the west of the Nile, is he easternmost extremity of the Sahara desert. The vegetation is predominantly concentrated on the flat wadi beds whereas the vast plateau and the moving sand dunes most often have no vegetation. The Arabic desert to the east of the Nile is a typical rocky desert with an intensely rugged relief. The vegetation displays a closer relationship to similar deserts on the Arabian peninsula than to the Libyan desert. The smallest desert is the Isthmic desert, situated to the north of the Arabic desert, and continuing in Asia in the central part of the peninsula of Sinai. The vegetation of this desert does not show any great differences being much influenced by the vegetation of the Libyan as well as Arabic desert; moreover the influence of the Negev desert may be also felt on the peninsula of Sinai. Oases form isolated islands in the Libyan desert. With regard to its position, the largest basis Fajtúm is a phytogeographical part of the Nile Valley. Other oases occur at greater distances from the Nile Valley. Since the primeval times there has existed an intensive agriculture in these parts; remains of original vegetation may be found in places with spontaneous issues of water which forms small lakes. Remarkable are climax communities including the palm Hyphaena thebaica. At the present time, the oases Charga and Dachla are strongly affected by the intensive agricultural development which makes the number of introduced weed species increase. Sinai, the mountainous part of the southern territory of the peninsula of Sinai, belongs to the most distinguished botanical territories of Egypt. There are many endemic species concentrated here together with a series of species occurring isolated from the territory of their distribution. The vegetation of the coast of the Red Sea does not display any rich variety of species as do the territories along the Mediterranen. There are, however, more marine Angiosperms. In the southern part of the coast occurs mangrove shrubbery, Gebel Elba, a mountain ridge along the Egypto-Sudanese boundary is the only territory with original accacia forests. For many species this is the northernmost point of their distribution. The mountain ridge Abenat, most probably is a separate phytogeographical whole situated on the boundary of Egypt, Libya and Sudan. It is quite possible that some relationship will be found to the neighbouring although higher mountain ridges, such as Tibesti or Gebel Marra.

Water from the Desert: Some Ancient Egyptian Achievements

IN egypt, 6000 years ago, when the latest rainy interlude began to wane, neo? lithic tribesmen from both sides flocked into the Nile Valley and there perforce exchanged pastoral existence for an agricultural one. The nomads who remained in the eastern desert could do little more than follow the scanty rains; west of the Nile, where there is no wadi network to concentrate the fall, the rain evaporated as it fell, the water table sank out of reach and the victory of nature over nomadic man was complete. Within few generations the peasant Egyptian had become, in Winkler's phrase, a stranger to the desert, the land of his forefathers. Some centuries later, when the kingdoms of Upper and Lower Egypt had united, the coordination of labour into vast gangs had strengthened man's hand, and now and again he began to fight back. To the deserts the new strangers returned to seek gold and copper, turquoise and ornamental stone; and, to sustain their assaults, water was necessary. The Bedouin cousins of the Egyptians had done no more than scoop out few shallow holes. Now, some unknown Pharaoh, with an architect far ahead of his time, attacked the problem in the grand style of the Pyramid Age. The oldest dam in the world.?Seven miles south-east of Helwan, in the Wadi el-Garawi, one may still see the abutments of the Sadd el-Kafara, the Dam of the Pagans, the first of its kind in history and one whose failure was so catastrophic that nothing of the sort was attempted again till over 3000 years had passed.1 Its age is not in dispute. From the style of its masonry and the nature of the potsherds lying in the workmen's huts about 200 yards from the site, Professor Schweinfurth who discovered the dam in 1885,2 Mr. Ernest Mackay who visited it in 1915 3 and Mr. Guy Brunton who accompanied me to the site in 1935,4 all agreed in ascribing its erection to the period of the Illrd or IVth Dynasties, from 2950 to 2750 B.C. For an initial experiment in dam construction, the size of the structure is surprising: I took the measurements quoted myself in June 1945. It is 348 feet long at the top and about 265 feet at the base; the lintel stood 37 feet above the lowest point in the wadi floor; and, passing through the great breach, one sees that the dam was composite. That is, it was made up of two separate rubble masonry dams, each 78 feet thick at the base, with space of 120 feet at ground level between them, which was later filled in with over 60,000 tons of shingle from the wadi bed and rubble from the hillsides. Beyond that, some 30,000 cubic yards of rubble masonry, say 40,000 tons, were employed in the construction of the upstream and downstream dams?a task that must have occupied the energies of many hundreds of men and animals for whole season in this desert place, 9 miles from the Nile cultivation.