A thermo‐hydro‐mechanical model for unsaturated soils based on the effective stress concept

A simple thermo‐hydro‐mechanical (THM) constitutive model for unsaturated soils is described. The effective stress concept is extended to unsaturated soils with the introduction of a capillary stress. This capillary stress is based on a microstructural model and calculated from attraction forces due to water menisci. The effect of desaturation and the thermal softening phenomenon are modelled with a minimal number of material parameters and based on existing models. THM process is qualitatively and quantitatively modelled by using experimental data and previous work to show the application of the model, including a drying path under mechanical stress with transition between saturated and unsaturated states, a heating path under constant suction and a deviatoric path with imposed suction and temperature. The results show that the present model can simulate the THM behaviour in unsaturated soils in a satisfactory way. Copyright © 2010 John Wiley & Sons, Ltd.     

Environmental isotope study of seawater intrusion in the coastal aquifer (Syria)

Seawater intrusion into the shallow aquifer in the Syrian coast, north of Latakia (Damsarkho, Ras Ibn Hani) and south of Tartous (Al Hamidieh, Ein Zarka) was studied using hydrochemical and isotopic techniques. The electrical conductivity (EC) distribution map north of Latakia revealed that mixing in this area is the consequence of a frontal intrusion of seawater within the fresh groundwater aquifer which, in turn, results from intensive pumping since the 1960s which has lowered the water table inland below sea level. In Ein Zarka, south of Tartous, in contrast, the EC distribution revealed that seawater intrusion is due to local up-coning as a result of intensive pumping. The deuterium and oxygen-18 relationship is that of a mixing line with a slope of 5.55, indicating an intrusion between freshwater and seawater. In addition, the relationship between oxygen-18 and chloride reveals that the mixing has a dominant role compared to evaporation process. The mixing ratios are estimated to be between 6 and 10% north of Latakia, while they do not exceed 3% south of Tartous. A tritium model was applied to compute the “mean transit time”, which is estimated to be around 10 years, on average, to reach the equilibrium that existed originally between the fresh groundwater and seawater, provided that severe pumping is completely halted and the aquifer is naturally recharged by rainfall and deep percolation of irrigation water, thereby allowing the restoration of the hydraulic gradient. This paper is dedicated to the memory of Dr. Y. Yurtsever.     

Relationship between point rainfall, average sampled rainfall and ground truth at the event scale in the Sahel

Geostatistical techniques are used to quantify the reference mean areal rainfall (ground truth) from sparse raingaugenetworks. Based on the EPSAT-Niger event cumulative rainfall, a linear relationship between the ground truth considered as the mean area rainfall estimated from the densely available raingauge network and the area rainfall estimated from sparse network are derived. Also, a linear relationship between the ground truth and point rainfall is established. As it was reported experimentally by some authors, the slope of these relationships is less than one. Based on the geostatistical framework, the slope and the ordinate at the origin can be estimated as a function of the spatial structure of the rainfall process. It is shown that the slope is smaller than one. For the special case of one gauge inside a fixed area or a Field Of View (FOV), an areal reduction factor is derived. It has a limit value which depends only on the size of the area and the spatial structure of the rainfall process. The relative variance error of estimating the FOV cumulative rainfall from point rainfall is also given.     

Configuration of the limestone aquifers in the central part of Egypt using electrical measurements

The Western Desert of Egypt is an area of natural expansion for agricultural, industrial, and civil activities. This expansion has led to a great demand for groundwater. In the central part of Egypt, on the western limestone plateau, vertical electrical sounding and borehole geophysical logging were conducted to delineate aquifer boundaries. The measurements were interpreted using the lithological information from the drilled wells as a constraining factor. Fractured chalky limestone sediments represent the main aquifer, which is covered by sand and gravel deposits and which rests directly on partially saturated and highly resistive massive limestone. Discontinuous clay layers, which overlie the aquifer unit, were detected in the southern part of the study area as well as a relatively thin marly limestone layer in the northern part. The integrated analyses carried out represent a significant and cost-effective method for delineating the main aquifer in this area. In turn, future well locations can be placed with more confidence than before, in accordance with the evaluation of the potentiality of the groundwater aquifers in the area. Although the groundwater is normally brackish, it can serve the acute demands for water, especially for agricultural purposes.     

Salt karst and tectonics: sinkholes development along tension cracks between parallel strike‐slip faults,Dead Sea,Jordan

This work deals with the tectonic interpretation of an alignment of more than 300 sinkholes stretching along the Jordanian coast of the Dead Sea, Ghor Al Haditha area. Its dimensions are 6 km long with a width of 600 m. Sinkholes appeared during the last decades as a consequence of the very rapid lowering of the lake level. The linear shape was inferred from ground collapse inventories carried out between 1991 and 2008. The lineament is replaced and analyzed in its structural setting at regional and local scales. Its direction (N 24° E) is sub‐parallel to the ones displayed by many focal mechanisms, especially the one associated with the earthquake of the 23 April, 1979 (mb = 5·1; N 20° E ± 5°), which is representative of all focal mechanisms calculated on a fault plane compatible with the general direction of the Jordan‐Dead Sea Transform fault system for the east coast of the Dead Sea area. The alignment of sinkholes is constituted by 13 minor linear segments separated by as many empty spaces. Four minor linear units present an en‐echelon arrangement from which one can deduce the presence of a local extensional stress field. In this context, the sinkhole locations provide information of subsurface discontinuities interpreted as hidden fractures. In a close future, such results could support the work of decision‐makers and engineers in the projected development of the area. Copyright © 2009 John Wiley & Sons, Ltd.     

Microearthquake studies in Egypt carried out by the geological survey of Egypt

Extensive microearthquake studies have been conducted in Egypt as a joint project between scientists from the Egyptian Geological Survey and Mining Authority (EGSMA) and U.S. scientists. At this stage, a great part of the data has been analyzed and two intensively active areas have been located: one in the Abu Dabbab area of the Eastern Desert, the second at the mouth of the Gulf of Suez near Gubal Island (Daggett et al., 1980). Both sites have been reported to be the epicenters of large earthquakes in 1955 and 1969, respectively. A few scattered earthquakes have also been located in the northern part of the Red Sea, some of which lie along its median axis (Daggett et al., 1986) adding to evidence for the medial opening of the northern Red Sea. After the occurrence of an earthquake (M = 5.5) in the Aswan region on 14 November 1981, continuous recording of the many aftershocks was carried out by EGSMA for about seven months from December 1981 to July 1982, when the temporary network was replaced by a network of telemetered seismographs installed and operated by Helwan Institute of Astronomy and Geophysics in cooperation with scientists from Lamont and Doherty Geological Observatory (LDGO). The majority of epicenters are concentrated in the vicinity of G. Marawa about 65 km upstream of Aswan Dam, along the E-W Kalabsha fault. The observed focal mechanism is consistent with a right-lateral strike-slip motion on the Kalabsha fault. Analysis of Aswan microearthquakes has been done by EGSMA in cooperation with scientists from California Division of Mines and Geology (CDMG).     

Geothermal potential of Egypt

One hundred and sixty samples of groundwater from nearly all parts of Egypt have been collected and chemically analyzed in order to assess the country's geothermal potential. The samples considered to be thermal include 20 wells (T > 35°C), 4 springs (T > 30°C) and 1 spring not included in the present inventory. The remaining samples, together with data from the literature, establish background chemistry. The hottest springs are located along the east shore of the Gulf of Suez: Uyun Musa (48°C) and 'Ain Hammam Faraoun (70°C). Additional warm springs are located along both shores of the Gulf of Suez and this region is the most promising for geothermal development. The Eastern Desert of Egypt, particularly the coastal area adjacent to the Red Sea has above normal heat flow ( ~ 72.0 < mWm⁻²) and therefore some geothermal potential although only one thermal well (Umm Kharga: 35.8°C) could be located, In the major oases of the Western Desert (Kharga, Dakhla, Farafra and Bahariya), the regional temperature gradient is low (< 20°C/km), but many of the wells tap deep artesian aquifers and produce large volumes of water in the 35–43°C range. Such wells constitute a low temperature geothermal resource. None of our samples in northern Egypt can be considered thermal including several reported “hot springs.” Application of the silica, NaKCa. and NaKCaMg geothermometers does not indicate the presence of a high temperature geothermal resource at any area we visited.     

Overexploitation and cumulative drought trend effect on Ras El Ain karstic spring discharge (Khabour Sub-basin,Syria)

The effects of climate change and overexploitation are being strongly perceived in the studied area and the springs discharge is obviously affected. In this paper, Ras El Ain spring discharge and precipitation were analyzed by normalized methods on an yearly timescale. The deficit of Ras El Ain spring discharge due to overexploitation factors and drought effects was estimated. Cumulative drought analyses were carried out using SPI10 and SQI10. Finally, the decreasing trends of the spring discharge due to the deficiency in rainfall were analyzed. The main results reveal that the annual mean deficit of Ras El Ain spring discharge due to overpumping was between 32 and 45%, whereas, annual mean deficit related to drought was between 22 and 35% on average, during the last 30 years (post-1984). The moving averages of SPI and SQI delineate very well the drought periods during last three decades. The cumulative droughts using SPI10 and SQI10 reveal that wet period (pre-1984) with positive values was characterized by high precipitation and spring discharge. Overexploitation period (1984–1989) is distinguished by decreasing SQI10 values whereas, SPI10 is almost stable. The response of the karst system to the precipitation signal has been changed, during the drought period (1990–2000), and the spring behaviour has been modified due to the first overexploitation period. Finally, overexploitation period (2001–2008) is related to the second phase of groundwater intensive pumping for irrigation purposes. Consequently, this period is completely catastrophic causing the drying up of the spring. The decreasing trends analyzed using DPI and DQI showed annual decreasing rates relative to the mean values of ?0.268% and ?0.105%, respectively. Thus, the results of theoretical model reveal that precipitation will decrease by about \(\hbox {DPI} = -20.7\)% and the discharge will decline by about ?9.2% by 2050. Consequently, the declining discharge due to climatic variation under natural conditions as pre-1984 was about 10%. Whereas, the catastrophic drying up of the spring was probably the consequence of the anthropogenic effects. Accordingly, it requires the development of sustainable water resources management program to reduce long-term drought risks, restore the groundwater reservoir and minimize the overexploitation effects on spring discharge.