Samy Ismail Elmahdy

Groundwater potential modelling using remote sensing and GIS: a case study of the Al Dhaid area, United Arab Emirates

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) DEM and LANDSAT images of spatial resolution 30 m were used to construct groundwater potential zones (GPZ) map by integrating geological fractures, drainage network, slope and relief, and convergence index maps of the study area. Weight and score of each map were developed according to their level of contribution toward groundwater accumulation and spatial distribution of groundwater wells. The area that has very high potential for groundwater is located at the foot of Oman Mountains and Al Dhaid Depression covering an area of about 59.33 km², which is 4.40% of the study area. Further hydrological map and data on hydraulic properties of shallow aquifer, as recorded from observation wells in the regions, have been used to validate the produced GPZ map. The validation result showed sufficient agreement between the produced GPZ map.

Remote sensing and GIS applications of surface and near-surface hydromorphological features in Darfur region, Sudan

Groundwater modelling and mapping in a region partly inaccessible using traditional techniques is practically very difficult, and time and cost consuming. However, integration of remote sensing and GIS enables more reliable mapping and analysis of hydromorphological elements such as palaeolakes. In the present study, a set of automated morphometric techniques of fitting a bivariate quadratic surface in a moving window of size 3 × 3 was used and modified to map and analyse hydromorphological elements in northwestern Sudan. Geomorphometry results indicate that the palaeodrainage network incision and depressions may have received most of the rainwater during late Quaternary wet phases. The results revealed that of the total 2000 km2 coverage of the unnamed depression, about 49.6% was classified as accumulation zone with a recharge area of about 992 km2, while the Wadi Fesh Fesh and Oyo depressions were shown to have the smallest areas of accumulation zone, approximately 31.3% and 37.3%, respectively. Validation of the methods was made by comparing trends and textural features from a Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) with 30 m spatial resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) DEM and 0.6 m spatial resolution Quickbird images and geological maps of the study area. The maps obtained showed a strong correlation, indicating that the proposed methods are very efficient tools for regional mapping and analysing hydromorphological elements in arid regions and remote and inaccessible regions.

Natural hazards susceptibility mapping in Kuala Lumpur, Malaysia: an assessment using remote sensing and geographic information system (GIS)

Intensive geological fractures and their associated karst features in tropical regions are often associated with unpredictable environmental and geotechnical engineering problems. This requires precise modelling using modern techniques. A 20 m spatial resolution Digital Elevation Model (DEM), a Geographic Information System (GIS) and Weighted Spatial Probability Modelling (WSPM) were integrated to predict the occurrence of flooding, landslides, sinkholes and earth subsidence in Kuala Lumpur, Malaysia. Five essential thematic layers were extracted using set of automated algorithms and then they were weighted. Layers included were geological fractures, stream network, micro-depressions, slope and lithological contact. All these thematic layers were assigned weights according to their level of contributions to the occurrence of flooding, landslide, sinkholes and earth subsidence. The map demonstrated that areas having very high geohazard susceptibility show an area of 4.155 km2 (8%), whereas the areas characterized by low susceptibility for the occurrence of geohazard is approximately 16.394 (31.5%) of total Kuala Lumpur area. The natural hazard probability model was validated by comparing its results with the published landslide locations and geophysical and geotechnical maps of Kuala Lumpur and the comparison showed strong agreement.

Influence of geological structures on groundwater accumulation and groundwater salinity in Musandam Peninsula, UAE and Oman

The hydrological setting and groundwater quality of Musandam Peninsula was studied to investigate the influence of geological structures on the groundwater accumulation and groundwater salinity. Five sets of modified morphometric maps were used to reduce errors and carry out the geological structures. The modification was modified by applying mean filter to the Digital Elevation Model (DEM) then applying Soble filter with 10% threshold and equalization enhancement. D8 and algorithms were used to reveal the drainage basins and drainage networks of the entire area. The algorithm determines into which neighbouring pixel any water in a central pixel will flow naturally. Flow direction in a DEM is calculated for every central pixel of input blocks of a 3 × 3 window, all the time comparing the value of the central pixel in the window with the value of its eight neighbours. The spatial association between geological structures and drainage networks was studied using 2D graph and rose diagrams. Flood basin model was applied to simulate the Arabian Gulf water intrusion into the coastal aquifer. The concentrations of solutes in groundwater samples collected from Wadi Al Bih well field and well locations were correlated with the geological structure trends and intersections. The results of the study reveal that the drainage basins, drainage network and groundwater quality are structurally controlled by subsurface geological structure displacements.

Automatic detection of near surface geological and hydrological features and investigating their influence on groundwater accumulation and salinity in southwest Egypt using remote sensing and GIS

This study employs two automated algorithms, the topographic fabric and the deterministic eight-node (D8), to reveal near surface geological fractures and their associated paleodrainages network from a 90 m DEM of the Shuttle Topographic Radar Mission sensor. The topographic fabric algorithm, which calculates the slope and aspect which define a vector normal to the earth’s surface and then compute direction cosines of normal vector at each point, was used to auto-detect fault zones. The deterministic eight-node (D8) algorithm, which determines in which neighbouring pixel any water in a central pixel will flow naturally, was used to delineate paleodrainages concealed beneath sand sheets. Seven sets of geological structures were recognized. Their major trends were found to be in the S46°W, S58°W, S81°W, N107°W, N–S, E–W and N152°W and share similar trends of the revealed paleodrainages. The results suggest a strong spatial relationship between the features extracted from DEM and groundwater potential.

Mapping of tecto-lineaments and investigate their association with earthquakes in Egypt: a hybrid approach using remote sensing data

This study integrates quantitative methods to detect surface and near-surface geological linear structures from digital elevation model. A set of altitude, slope and shaded relief maps was enhanced by applying Sobel filter with 10% threshold and percentile stretch to detect geological fractures and their displacements over regional scale. Topographic fabric grain algorithm, which classifies point lines into the ridge/valley and quantifies the degree to which all the ridges and valleys are aligned in the same direction, was used to auto-detect lineaments. About 1300 linear features were computed and their orientations were statistically analysed using rose diagrams. The enhanced morphometric maps successfully visualized fault zones and their displacements and detected the regional fault zones cutting across the entire Egypt. Their trends were found to be in the NE–SW, NNE–SSW, NW–SE, NNW–SSE, N–S, E–W and WNW–ESE directions. The results obtained using the integrated methods were compared with those in geological and seismic maps of Egypt and showed strong agreement in several places. This proposed method may be useful for mapping concealed geological structures, where geophysical surveying is difficult and geological information not available.

Application of a weighted spatial probability model in GIS to analyse landslides in Penang Island, Malaysia

In the current study, Penang Island, which is one of the several mountainous areas in Malaysia that is often subjected to landslide hazard, was chosen for further investigation. A multi-criteria Evaluation and the spatial probability weighted approach and model builder was applied to map and analyse landslides in Penang Island. A set of automated algorithms was used to construct new essential geological and morphometric thematic maps from remote sensing data. The maps were ranked using the weighted probability spatial model based on their contribution to the landslide hazard. Results obtained showed that sites at an elevation of 100–300 m, with steep slopes of 10°–37° and slope direction (aspect) in the E and SE directions were areas of very high and high probability for the landslide occurrence; the total areas were 21.393 km2 (11.84%) and 58.690 km2 (32.48%), respectively. The obtained map was verified by comparing variogram models of the mapped and the occurred landslide locations and showed a strong correlation with the locations of occurred landslides, indicating that the proposed method can successfully predict the unpredictable landslide hazard. The method is time and cost effective and can be used as a reference for geological and geotechnical engineers.

Geological Lineament Detection, Characterization and Association with Groundwater Contamination in Carbonate Rocks of Musandam PeninsularUsing Digital Elevation Model (DEM)

Geological lineaments play vital role in groundwater recharge, groundwater discharge toward the sea. For this purpose, topographic fabric algorithm which uses a digital elevation model (DEM) to create maps of ridges and valleys was used to carry out all geological lineaments crosscutting the entire Musandam Peninsula, UAE and Oman. Six sets of geological lineaments deform the carbonate aquifer of Musandam Peninsula, UAE and Oman. Their orientations were found to be in the NW-SE,NNW-SSE,NE-SW,NNE-SSW, WNW-ESE and E-W directions. The most notable of these lineaments are tensional and dipping to the E-W, NNE-SSW and N-S. The extracted geological lineaments were spatially correlated with previously groundwater samples collected from Al Bih well field. The results of the study reveal that the Musandam carbonate aquifer is structurally controlled by geological lineaments that have been produced by successive tectonic events, significantly influencing groundwater salinity and groundwater temperature of Al Bih well field indicat- ing the efficient of the proposed method.

Groundwater of Abu Dhabi Emirate: a regional assessment by means of remote sensing and geographic information system

Mapping of geological, topographical, and hydrological elements is critical for understanding and assessing the regional hydrological setting in an arid region. In this study, a synergistic approach has been developed, which uses a combination of remote sensing data and geographic information system (GIS) to map factors controlling groundwater recharge, discharge, and quality across the Abu Dhabi Emirate. The Spectral Angel Mapper (SAM) algorithm, which uses a n-D angle to match the pixels to reference spectra, was used to map new water-bearing rocks, and the deterministic eight-node (D8) algorithm, which allows flow to only one of the eight neighbors based on the direction of steepest descent, was used to map paleochannels. The terrain category was applied to simulate seawater intrusion from digital elevation model (DEM). New maps of lithology, normalized difference vegetation index (NDVI), and paleochannels were derived and interpreted from multi-sources of remote sensing data. The study indicated that the area was produced by a fluvial and eolian process and recharged by local, intermediate, and regional flows. The results showed that the Oman and Hafeet Mountains are the natural sources of groundwater recharge as well as HCO3, Ca, Na, and Mg in groundwater. The mapped factors were spatially correlated with hydrologic anomalies observed in groundwater wells. The integrated approach is timely, cost-effective, and can be used in arid regions for numerical modeling as well as water balance analysis.

Remote sensing of the Grand Ethiopian Renaissance Dam: a hazard and environmental impacts assessment

ABSTRACT The Grand Ethiopian Renaissance Dam (GERD) is constructed in a mountainous area where limited information has been collected on key environmental factors and which is lacking of information about site condition, hazards and environmental impacts. To deal with problems, the Shuttle Radar Topographic Mission (SRTM) DEM and Advanced Land Observation Satellite Phased Array type L-band Synthetic Aperture Radar (ALOSPALSAR) were used to map factors that can lead to the GERD failure and predict the flooded area in Sudan and seawater intrusion in the Nile Delta, Egypt. The results showed that the Nubian Block and the GERD site are structurally controlled by sets of faults. Their trends are in the NNE–SSW, NE–SW, and NNW–SSE directions and share the similar trends with the shear stress and African Rift, which created some alarm. The results indicated that the maximum extent of the Sudanese inundation area, as estimated from a DEM using a flood basin model, was about 667,228 km2 along the Blue Nile River and was at high risk. The results also showed that one-third of the Nile Delta will experience seawater intrusions when the groundwater table depletes 5 m below sea level.