مجلة النيلين لعلوم الارض

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Flash Floods Risk Assessment of Sharg Alneel area, Khartoum State, Sudan Using Remote Sensing, GIS and Geophysical Techniques
(جامعة النيلين, 2017) Esamaldeen Ali; Khalid A. Elsayed Zeinelabdein; Khatab A. Rahamtallah
Abstract This study was carried out to investigate the geological sources that may cause the flash floods of Shareg Alneel area in the eastern part of Khartoum City, Sudan which lead to damage of property and the infrastructures of the residential areas. In this study, remote sensing technique using Landsat-8 images together with Shuttle Radar Topography Mission (SRTM) elevation data and geophysical techniques (resistivity and gravity) have been adopted. Wadi Soba, Green valley and Wadi El Sileit are the main seasonal water courses in the study area that drain into the Blue Nile with a regional parallel pattern. The results show that relatively steep slope from east to west may represent one of the factors contributing to the flood hazard during the rainy season. Also, it can be noted from band ratio technique that high concentration of clay sediment is located close to the River Nile and along these three valleys. This result was confirmed by resistivity technique which shows an existence of considerable amount of clayey sediments that obstruct water infiltration. The residual gravity reveals that the three valleys are characterized by relatively lower gravity anomaly indicating thicker sediments than the surrounding plains. From the obtained results, Flood hazard map has been created which divided the area into low, moderate and high risk areas. Accordingly, it was conducted that that the residential areas were superimposed over high risk zones. This study recommends re-planning of residential areas and construct dykes in the upper stream of the main valleys to decrease the flood hazard effects.
Litho-Tectonic Evolution around Third Cataract, Sudan: An integrated Remote Sensing, Lithological, Structural and Geochemical Approaches
(جامعة النيلين, 2017) Esamaldeen Ali; Mohamed Y. Abdegalil; Abu Elhassan Musa; Nuha E. Mohamed
Abstract This Study is focused on the geology of the area around the Third Cataract, Sudan. In terms of combined remote sensing, petrological, structural and geochemical criteria this article presents detailed lithological and tectonic evolution of this region. For preliminary visual interpretation of the different lithological units and structural elements a digital image processing has been applied using Landsat 8 OLI images that are verified by precise ground truthing. Petrography, geological and structural field relationships have led to preliminary classification of rock units into: Undifferentiated orthogneisses and migmatites; Low to medium-grade metavolcano-sediments; Syn-orogenic intrusions; Late to post-orogenic intrusions; Cretaceous sandstone formation; Cainozoic volcanics and Quaternary to Recent sediments. Geological map has been created at scale of 1:75,000. In this study, three deformation episodes are identified (D1, D2 and D3), where D1 is associated with the formation of tight to isoclinal recumbent fold (F1) with north-dipping fold plane and sub horizontal trending axes verging to the east. Deformation took place in green schist-facies rocks that is thought to be related to the arc-accretion event. D2 gave rise to open upright fold (F2) which folded the axial surfaces of (F1) with fold axes plunging gently to the NNW. NNW–SSE sinistral strike slip movement is a main characteristic of D3 deformation. The geochemical results show a clear calc-alkaline trend of the metavolcanics units that were derived from volcanic arc magmas. Whereas the granitic rocks classify as calc-alkaline metaluminous to slightly peraluminous, and is considered as I-type granites. Rb versus (Y+Nb) discrimination diagram indicates volcanic arc granites.