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Ain Shams University (2019)

Characteristics of the Aeolian Deposits and Their Effects

Elmenshawy, Ehab Abdelsalam Mohamed

Titre : Characteristics of the Aeolian Deposits and Their Effects on Sustainable Development in Some Areas

Auteur : Elmenshawy, Ehab Abdelsalam Mohamed.

Etablissement de soutenance : Ain Shams University

Grade : Doctor of Philosophy (PhD) in Geology 2019

The present study deals with the hazard effects of aeolian deposits on some selected areas in the east Nile Delta (Khanka and Salhiya regions). The study area lies between Latitudes 30 00 00 to 30 50 00 N and Longitudes 31 00 00 to 32 20 00 E covering an area 4136 Km2. The extremely flat surface of the study area is covered by aeolian deposits. Sand dunes are variables in size, patterns and types. These are represented by linear, obstacle dunes and nabkas. The axis of linear dunes oriented toward northwest (NW)- southeast (SE) and east (E)- west (W) directions. This study aims to identify the types, patterns and distribution of aeolian deposits to clarify the mutual environmental impacts of the aeolian sand deposits and the development projects in the study area. The studied dune sands show unimodal distributions with modal classes fall into medium sand size grade with rarely fine and coarse sand size. The statistical grain size parameters of the studied sands are similar. The collected samples are medium sand sized, moderately well to moderate sorted, fine skewed and mesokurtic except the crest of Khanka dunes which are leptokurtic. The roundness and sphericity of Khanka and Salhiya samples are similar in their percentage and mainly fall in subrounded to subangular classes with high sphericity and show relatively higher percentages in Salhiya than Khanka dune sands. Surface of quatrz grains display both mechanical and chemical features. These features are commonly represented by V-shaped, dish shaped depressions, upturned plated, cracks, stepped fracture, upturned plates with silica dissolution (deep holes and linear and triangular grooves) and silica as well as iron precipitations. The mineralogical investigations include the light and heavy minerals identification. The light minerals are composed of quartz with minor of feldspar and mica. The heavy minerals are represented by opaques (ilmenite, magnetite and leucoxene with minor percent of titanite and trace of gold) and non-opaques (zircon, amphiboles, rutile, garnet and pyroxene with rare percent of monazite and epidote). Very rare percent of kyanite, andalusite, apatite and sillimanite are recorded. The analysis of wind regime refer to the predominance of two prevailing wind directions ; northeast and northwest. The most erosive and effective in sand transport is NW direction, which is responsible for drifting sand toward SE direction by 1470 m3 Km-1 year-1 in Khanka area. Northwest wind direction is responsible for drifting sand toward SE direction by 2030 m3 Km-1 year-1 in Salhiya area. Drift Potential (DP) and Resultant Drift Potential (RDP) range from low to high wind energy environment. The wind variability ranges from intermediate to high with unidirectional wind regime. The axis of dune belts in the study areas are match with the annual wind regime. The rate of elongation and direction of linear sand dunes measured by surveying the whole dune outline using total station instrument during different period (12-2013 to 6-2016) is 2.2 and 0.49 m y-1 toward SE direction and the lateral displacement of crest axis is 0.54 and 0.16 m y-1 toward west and east directions in Khanka and Salhiya areas, respectively. The lateral shifting of leeward side is 0.20 and 0.03 m y-1 toward west and east directions in Khanka and Salhiya, respectively. The surface of dune on windward and leeward sides shows deposition and erosion volume of sand during different times for 2 and half years starting from 12-2013 to 6-2016. The volumes of sand during 12-2013 to 6-2016 is variable in both windward and leeward sides but mainly show that the depositional volume is higher than erosional volume which is indicating for activities of dunes and increase their size and extension. The elongation rate of crest axis of linear dunes and direction are determined by using satellite images during different periods (1984, 1989, 1998, 2006 and 2016). The results show gradual decrease of elongation rate with time toward SE direction. The rate of elongation in Khanka and Salhiya areas are 0.0, 9.3, 4.2, 4.7, 3.1 m/y and 0.0, 6.2, 3.1, 0.9 and 1.5 m/y ; respectively. The human activities during 1984 to 2016 led to the disappearance of crest axis of linear dunes in the study area. Also, the human activities were higher during 1998 than other periods in Khanka region, while the highest human activities were recorded during 1989 in Salhiya region. In the study area, agricultural and urban activities increase on the expense of dunes and desert areas. The agricultural areas increased than urban areas in the dunes of Salhiya meanwhile urban areas increased than agriculture covers in Khanka dunes. Temperature changes of Khanka and Salhiya regions for the same period increase for minimum and maximum during 1998 to 2006. Salhiya region shows low relative increase than Khanka region, this is due to increase of reclamation areas than urban areas and vice versa in Khanka area.

Présentation étendue (EULC)

Page publiée le 2 avril 2020