Abstract
Catastrophic mass movement of rocks and torrents affected the Abu El-Reesh area, northeast of Aswan City. The present article aims to evaluate the potential catastrophic movement of rocks, delineate the risk zones, and suggest suitable solutions to avoid the potential risks in this area. The sedimentary succession of Abu El-Reesh area is mainly represented by the Nubian sandstone sequence of Upper Cretaceous (up to 60 m thick) forming a huge scarp at the eastern border of the study area. This sequence comprises two vertically successive rock formations: Timsah Shale Formation and Umm Barmil Sandstone Formation. The Timsah Shale Formation forms the lower part of the sedimentary succession with a thickness of 6-40 m. It is composed of shale beds with intercalations of sandstones, siltstones, and mudstones. This formation is overlain by the Umm Barmil Sandstone Formation, representing the cap rock of the succession, with a thickness of 4-20 m. The western scarp face has an irregular concave slope, with slope angles ranging from 22 degrees to 46 degrees in the lower part of scarp and become steep (60 degrees -86 degrees ) at its upper part. The drainage patterns are mainly coarse dendritic and discharge into the Nile River, passing through densely populated zones. These zones are exposed to the torrents during rare rainfall events. Three sets of vertical joints (trending NNW, NNE, and WNW) dissect the cap rocks and intersect with the horizontal bedding planes to form separated cubes and polygonal blocks. Potential catastrophic movement of rocks in Abu El-Reesh area is related to several reasons, including: existence of competent sandstones underlain by incompetent shales, dissection of the coherent cap rock due to intersection of vertical joint sets and bedding planes, presence of exposures with steep slopes, rainfall, and human activities (mining works, sewage water, and irrigation). Based on the dominance of either one or more of these reasons, three subareas (El-Khalasab, El-Shadeeda and El-Aqaba) represent the main risk zones, subjected to rock movements and torrents in the study area. Several solutions have been suggested for avoiding the risks related to the potential catastrophic movement of the rocks and torrents in the study area. The fractured rock masses at the top of scarp should be released either mechanically or manually. All buildings that were built on the slope surface of the scarp should be removed. Also, buildings which were constructed in the inlets of wadis and through the rain spillways should be removed. An unsafe boundary separating safe building borders from unsafe zone (with average width 50 m from the base of scarp) is delineated. As a result, resettlement for people living in this unsafe zone should be transferred to another safe area. Copyright 2010 Saudi Society for Geosciences