Assessment of Landslides of the Hillslopes in Makkah Using Remote Sensing and GIS Techniques
Al Harby, K., El Bastawesy, M., Habeebullah, T., and Mandour, M. (2012). Assessment of Landslides of the Hillslopes in Makkah Using Remote Sensing and GIS Techniques. The Journal of American Science, 8(3), pp. 46-53. (ISI Impact Factor 2012: 0.5)
Abstract:
The landslides of Makkah hillslopes have been assessed using remote sensing, GIS and fieldwork techniques. The geology and geomorphology of Makkah is controlled the urban development of the city on limited alluvial plains, footslopes and rock-cut parcels of the piedmonts. High resolution satellite images were utilized to determine rock-cut slopes, land use and land cover maps, which were created by geographic information system (GIS) and verified in the field. The development of regolith covers hillslopes is controlled by the dominant geological setting, structures, weathering mechanisms and palaeohydrological setting. The stability conditions of debris materials on hillslopes have been affected by the ongoing rock-cutting processes of the piedmont. The simple slopes covered by regolith of different shapes and dimensions are in stable conditions, as the surface roughness, which is high and could retain the limited landslides. On the other hand, compound slopes are mantled by abandoned terraces of various-sized sediments and assigned as the most susceptible for landslides. The relict palaeohydrological features and abandoned terraces are being gullied by occasional heavy storms and resulting overland flow and runoff. The extent of gulling, mud and debris flows and the buildup of debris at talus cones are characterized by high spatial variability. Furthermore the landslides also depend on the morphometrical parameters of abandoned terraces, profiles of hillslopes and upslope contributing areas of the overland flow and runoff. However these slow and occasional landslides may have very limited impact on urban areas, but further complication could arise as, for example, a key electricity distribution station in Makkah is constructed on the top of local piedmont being gullied by occasional storms. Moreover, the buildup of dumping sites for waste rock fills has also induced significant changes in the landforms of Makkah, which has blocked certain active alluvial channels used to covey flash floods.
[Kalid Al Harbi, Mohammed El Bastawesy, Turki Habeebullah and Mousad Mandour. Assessment of Landslides of the Hillslopes in Makkah Using Remote Sensing and GIS Techniques] Journal of American Science 2012; 8(3): 46-53]. (ISSN: 1545-1003). http://www.americanscience.org Paper information: submitted 21 December 2011, Acccpeted 13 March 2012.
Key word: Landslides, Hillslopes, Makkah, Remote Sensing, GIS
Introduction
The landslides are very complex process; the instability of slopes can be triggered by variety of mechanisms and causes including, but not limited to, earthquakes (Refice and Capolongo, 2002), dynamics of soil moisture (Talebi e al., 2007), weathering mechanisms (Chigira et al., 2002) and heavy precipitation processes (Tarolli et al., 2011). This control is likely to vary with the composing geological materials structures, and the landform (Clague, 1980). However, the currently activeprocesses are determined, to some extent, by the form evolution; the slopes may possess relict features formed under different climatic conditions. Moreover, denudation, transportation and accumulation of landslide materials are strictly applicable to certain points throughout the whole slope length and vary considerably over space and time. The scale of landslides may range from spontaneous creeping that only extent few meters in dimension, to rare gigantic slides or avalanches, which could cover up to several kilometers in size and thus affecting sizeable populations (Horn and Scott, 1975). The detritus of landslides is also various, and it can be entirely composed of rock fragments, others of soils only, and a few are of mixed materials. For considerations of effects on people and engineering works, the speed at which a landslide develops and moves is the single most important feature (Youssef et al., 2009). Few defenses are available against rapid and unexpected movements that frequently result in damage, injuries and fatalities. However, landslides which move very slowly or over longer period of times will seldom cause causalities, as mitigation measures can be taken. Although the impact of landslides can be considerable, but the processes itself is highly complex and therefore assessment can be also difficult (Carrara et al., 1991).
Therefore, different methodologies are being proposed to assess susceptibility of various landslide hazards (Saha et al., 2002). The simplest approach to analyze a landslide depends on direct field observation of mass movement occurred during past landslides, or mapping the interpreted recent landslides from available aerial photographs and high-resolution satellite images (Wieczorek, 1984). Monitoring of susceptible areas can be achieved using installed survey networks and control stations, where target prisms are placed on and around areas (i.e. on stable ground) of anticipated instability. Thus, angles and distances between them are regularly measured to detect any movement on slopes and to obtain quantitative estimates. Additionally, air born Synthetic Aperture Radar (SAR) can also be used to generate a high quality Digital Elevation Model (DEM), and to detect delicate surface disturbances (e.g. Furneu and Achachi, 1996; Massonet, 1997).
These different observations and measurements can be correlated with other morphologic and the driving force to obtain quantitative index for landslide analysis, and to propose a numerical scheme for landslide analysis (Montgomery, et al., 1991). Geographic Information System (GIS) proved very efficient to compute certain morphometrical parameters from DEM as well as compiling, manipulating and analyzing different co-registered parameters (Terlien et al., 1995) Of course the weighted parameters are very subjective and elaborated on certain experience, types of landslides and geological and geomorphologic setting, thus their regional application can be totally misleading. Therefore, it remains necessary to understand control and distribution of landslides in certain areas to determine the potential hazard. This paper will investigate the susceptible landslides of Makkah city, which is mainly built on sets of alluvial channels bounded by steep mountain ranges. The complex geological and geomorphologic setting for the study area has confined the urban growth of Makkah at the foot slopes of surrounding mountains. Notably, considerable areas of piedmonts and foot slopes are being cut and cleared for urban development. Therefore, it is necessary to assess the human impact on the stability and equilibrium conditions of Makkah hillslopes, and to determine the potential landslide hazards.
with the Red Sea rifting (Fig 1). The geomorphology has controlled the unique urban pattern of Makkah metropolitan city, which has sprawled in radial direction on the limited surface areas of the complex alluvial channels always being separated by the steep mountain ranges. It is estimated that approximately 9000 hectares of alluvial channels and footslopes of the mountain were converted into urban areas from 1978 to 2000 (Al Ghamdi and Al Naggar, 2002). The Wades of Makkah dissecting the mountain ranges are characterized by complex and interlocking patterns. This complex pattern of intersecting alluvial areas are very common in the dry land setting and reflect the morphotectonic evolution of these drainage basins, where the paleo-channels (i.e. palaeohydrology) were used to flow through different directions than the contemporaneous flow pathways (e.g. El Bastawesy et al., 2010). However, the restricted attachment of urban neighborhoods, were overcome through tens of tunnels and rock-cut corridors through these mountains ranges. Because of the disappearance of land parcels suitable for urban development, it is now common in Makkah to cut the piedmont and footslopes of the neighbouring mountains in order to create new suitable plots for buildings, especially in the areas near the Holy Mosque of Makkah. Similarly, the footslopes of the mountains bordering the Holly places (i.e Arafat, Muzdalepha and Mena) were also cut to provide more spaces and infrastructures for millions of pilgrims are annually gathered for few days to perform Hajj. Due to the importance attached to the holly places, multiple rock fall mitigation measures were adopted including, concrete barriers, berms and Gabion walls, grouted dowels and shotcrete lining (Fig 2). While mitigation measures in the other urban areas included terracing of the cut-slopes and supporting some cut-slopes with shot Crete lining and addition to considering a safety-zone between urban and the cut-slopes.
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