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Morphologic Characteristics and Migration Rate Assessment of Barchan Dunes in the Southeastern Western Desert of Egypt

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Morphologic Characteristics and Migration Rate Assessment of Barchan Dunes in the Southeastern Western Desert of Egypt Geomorphology 257 (2016) 57–74 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph Morphologic characteristics and migration rate assessment of barchan dunes in the Southeastern Western Desert of Egypt M.A. Hamdan, A.A. Refaat ⁎, M. Abdel Wahed Geology Department, Faculty of Science, Cairo University, Giza, Egypt article info abstract Article history: This work explores the morphologic characteristics of aeolian dune sand in the southeastern part of Western De- Received 3 May 2015 sert of Egypt. It aims to assess the movement of barchan dunes and evaluate their environmental influence on the Received in revised form 6 December 2015 Toshka Project. Morphometric investigation of barchan dunes in the Toshka area revealed that most barchans Accepted 30 December 2015 have high length/width (a/c) ratios (fat to pudgy), while one-fifth of the studied barchans have lower a/c ratios Available online 31 December 2015 and so appear normal in their morphologic forms. Statistical analysis of the main parameters of barchan dunes in Key words: Toshka and other desert regions in the Kharga (Egypt), Kuwait, Southern Morocco, California and Southern Peru Barchan dune demonstrates that barchans of the Toshka area are distinctive in their appearance. They are characterized by dis- dune migration tinct aspect with higher values of length and width and greater growth in height. The high-energy wind environ- dune encroachment hazard ment in addition to the large amount of drifting sand are principal factors responsible for the unique shape of Western Desert of Egypt Toshka barchans. The migration rate of barchan dunes in four chosen test locations, within the central and western Toshka area, ranges from about 3 to 10.82 m/year. The calculated average migration rate of these dunes is about 6 m/year in a SSW direction. Sand encroachment is more extensive in the central and western parts of the investigated Toshka area. Risk evaluation of sand dune movements in the southeastern part of the Western Desert points to medium to high sand encroachment risk values. These may represent serious hazards to the newly-established Toshka Project, threatening roads, as well as cultivated lands in the area. © 2015 Elsevier B.V. All rights reserved. 1. Introduction characterized by high dune sand accumulation. The area has been cho- sen to serve as a model for the assessment of dune migration because it Many areas in the Western Desert of Egypt are characterized by high is affected mainly by strong trade winds which exert a strong control on accumulations of wind-blown sand (Fig. 1). Modern aeolian sand of the the mechanism of dune formation as in the eastern range of the Great Western Desert of Egypt has been the subject of scientific interest since Sahara Desert (Besler, 2008). It also represents the focal area of many the beginning of the 20th century (e.g. Beadnell, 1910; Ball, 1927; dune streams and sand accumulations that migrate from other regions Bagnold, 1931, 1941). Numerous geologic, geomorphologic, textural, of the Western Desert of Egypt into the northern Toshka area (Fig. 1). mineralogical, geochemical and source-area genetic studies of the Hence, the Toshka area is considered to be an ideal region for dune mea- sand dunes followed (e.g. Embabi, 1970; El-Baz et al., 1979; Besler, surements and can be used as a model for other regions in the Western 1986, 1998, 2000, 2008; Haynes, 1989; Stokes et al., 1998; Hamdan Desert of Egypt and North Africa. and Refaat, 1999; Hamdan, 2003; El Gammal and Cherif, 2006; Abou Sand dunes are a common feature of many desert regions all over El-Magd et al., 2013; Khedr et al., 2013a, 2013b; Refaat and Hamdan, the world and they may exist in many different types. Barchan dunes 2015; Hamdan et al., 2015). Several studies have been concerned with are the simplest and most common dune type as it maintains a crescent estimating the rate of desert dune movement in many areas of Egypt, shape and occurs in areas characterized by steady winds coming from a especially in the Western Desert (Table 1). Sand dune movements are similar direction throughout the year, providing there is not enough considered to be a specific threat to roads, irrigation networks, water re- sand to cover the entire regional surface (Sauermann et al., 2000). Bar- sources, urban areas, agriculture and infrastructure of the Toshka pro- chan dunes are well developed in many parts of the Egyptian Western ject (Wahby, 2004). Desert, including the Toshka area, as well as in many deserts areas not The southeastern part of the Egyptian Western Desert is largely rep- only on the surface of the Earth (e.g. Bagnold, 1941; Finkel, 1959; resented by the Toshka area; it covers about 50,000 km2 and is Long and Sharp, 1964; Hastenrath, 1967; Hesp and Hastings, 1998; Sauermann et al., 2000; Parteli et al., 2007) but also on the surface of ⁎ Corresponding author. Mars (e.g. Goudie and Bourke, 2008; Bourke and Balme, 2008). More- E-mail address: [email protected] (A.A. Refaat). over, several types and forms of barchan exist in these deserts, http://dx.doi.org/10.1016/j.geomorph.2015.12.026 0169-555X/© 2015 Elsevier B.V. All rights reserved. 58 M.A. Hamdan et al. / Geomorphology 257 (2016) 57–74 Fig. 1. Map of the Western Desert of Egypt showing the distribution of the major sand dune fields (modified after El-Baz, 1979). The study area is located in the southeastern part of the Western desert of Egypt. Numbers inside the circle refer to dune migration rates of the Toshka area and other regions in the Western Desert of Egypt where arrows refer to the direction of dune migration at each area. The number at the head of each arrow refers to the corresponding reference: 1 = Beadnell (1910);2=Ashri (1973);3=Embabi (1979);4=Sharaky et al. (2002); 5 = El Gammal and Cherif, (2006); 6 = Abou El-Magd et al. (2013); 7 = Present study. depending upon several factors, such as wind strength and direction, Western Desert of Egypt. Finally, the degree of sand dune encroachment amount of drifting sand, topography and vegetation. The current and its effect on the Toshka Project is evaluated. paper is a comparative study that highlights the main morphometric characteristic features of Toshka barchans and other barchan shapes from different deserts of the world. Evaluation of the main factors 2. Geomorphologic features that control the morphology and existence of these dunes are discussed. The study area is located in the southeastern part of the Western De- A further aim of this study is to investigate the distribution of aeolian sert of Egypt between 22° and 24° 00′ Nand30°15′ and 33° E (Fig. 2). dune sands in the Toshka area and to identify their types using remote With the exception of Sinn el Kadab Plateau and its pediments, which sensing and GIS techniques. The study assesses the rate of barchan lie more than 300 m above sea level and bounding the Toshka Depres- movement in the Toshka area in comparison with other regions in the sion from the north, the study area is relatively flat and most of it is M.A. Hamdan et al. / Geomorphology 257 (2016) 57–74 59 Table 1 Rate of dune movement in the east of the Nile Delta and different locations in the Western Desert of Egypt, with their references. Location area Time period (year) Rate (m/year) Reference East of the Nile Delta 1898–1990 4.5 Cornish (1900) Kharga Depression 1908–1909 15 Beadnell (1910) Kharga Depression 1971 12 Ashri (1973) Kharga Depression 1978 20–100 Embabi (1979) Dakhla Depression 1990 0.5–14 Sharaky et al. (2002) Abu Moharik dunes 1974, 1984–2001 17.5 El Gammal and Cherif, (2006) –northern of the Bahariya oasis 7.5 –middle part of the dune field 11.5 –southern end near the Kharga depression Toshka area 2000–2006 1.3–19.3 Abou El-Magd et al. (2013) 1987–2007 6.024 Present study occupied by the Toshka Plain (Depression), ranging in elevation from el Kadab Plateau and Lake Nasser from the east, while the Egyptian- 150 to 250 m above sea level. Sudanese Border represents its southern boundary. The evolution of the Toshka Plain is mainly controlled by the existence of a series of 2.1. Sinn el Kadab Plateau folds and faults (El Shazly et al., 1977). The Toshka Plain is characterized by outcrops of isolated Nubian sandstone hills and short, wide wadies The extensive Sinn el Kadab plateau, which is underlain mainly by that in the past drained into the Nile Valley. Precambrian igneous and limestone, consists broadly of horizontal beds of late Cretaceous to metamorphic rocks, early Cretaceous Nubian sandstone and Quaternary early Eocene age. It is bounded eastwards and southwards by a precip- Nile sediments are all exposed in the Toshka area (Fig. 3). itous escarpment, overlooking the Nile Valley from its eastern side, while northwards the plateau extends beyond the area under consider- 2.3. Lake Nasser ation to the Kharga Depression (Fig. 1). The escarpment is mainly con- trolled by major faults that are generally trending in N-S and E-W Lake Nasser, the world's largest man-made lake, is a reservoir in the directions (Fig. 3). course of the River Nile, formed by construction of the Aswan High Dam in 1960. It is located at the border Egypt and Sudan between latitudes 2.2. The Toshka Plain (Depression) 21.8°N to 24.0°N and longitudes 31.3°E to 33.1°E. Its surface area is about 5200 km2 with a maximum water capacity of 165 km3 and a This plain occupies the central part of the study area and attaining an mean depth of 25 m; its surface elevation is 175 m above sea level.
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