Morphotectonic controls on hydro-environmental hazards in rift basins: a case study from Southern Suez Canal Province, Egypt

Abstract

Background

The Southern Suez Canal Province (SSCP) has recently encountered hydro-environmental hazards such as water logging and soil salinization, both of which impede the efficient land use planning.

Purpose

This study aims to assess the hydro-environmental threats to SSCP and identify the key factors that contribute to their occurrence. Previous research has demonstrated that the Gulf of Suez Rifting-related tectonic movements have a significant impact on the entire SSCP region. The influence of tectonic setting on the development of hydro-environmental dangers was not examined in almost any studies.

Methods

Remote sensing, GIS, hydrogeological, and geophysical techniques are used to identify and assess topographic, hydrogeological, and tectonic variables that affect hydro-environmental hazards in the SSCP.

Results

This study found that the distributions of water logging, saturated soil salinization, urban areas, and vegetation cover changed more dramatically between 1984 and 2015. The expansion of water logging area (+10.68 km² rating +0.35 km²/y), saturated saline soil (+24.40 km² rating +0.79 km²/y), and urbanized area (+58.43 km² rating +1.89 km²/y) is strongly associated to the expansion of vegetation cover (+188.13 km² at a rate of 6.07 km²/y). This could imply that growing agricultural expansion and urbanization are influencing the dominance of hydro-environmental hazards in SSCP. The distribution of water logging features identified on the land cover map corresponds closely to a buried horst structure dominating the middle part of the surveyed area.

Conclusion

The lowland water logging features of the SSCP provide support for the hypothesis that the buried horst structure that dominates the Miocene and pre-Miocene strata has an impact on the thickness and groundwater flow regime of the quaternary aquifer that lies above. The present study came to the conclusion that the shallow depth of groundwater, the vast expanse of newly cultivated lands, the impervious clay layer beneath the thin topsoil layer, and the low topography are the key factors influencing the development of water logging and soil salinization features in SSCP.

Introduction

Numerous studies have been conducted to examine the relationship between tectonic structures, geomorphology, and groundwater (Taylor and Howard 2000; Ayazi et al. 2010; Elmahdy and Mohamed 2014 and 2015; Kaplay et al. 2017; Arnous et al. 2020; Haque et al. 2020; Hegazi et al. 2023). These studies proved that structural features such as folding and faulting have a significant impact on groundwater flow patterns. The threats posed by the hydro-environment are significantly influenced by tectonic and structural features, particularly in dry and semi-arid regions (El-Rayes et al. 2017). Fractures, faults, and shear zones increase permeability and improve fluid transport through fractured and sheared rocks, which has several hydro-environmental consequences (Barton et al. 1995; Caine et al. 1996; Evans et al. 1997; Gudmundsson et al. 2001; El-Rayes et al. 2020; Arnous et al. 2020). The SSCP was greatly influenced by tectonic movements that occurred during the evolution of the Gulf of Suez rifting, which occurred in the late Oligocene and continued into the early Miocene (Bosworth et al. 1998). These tectonic deformations were crucial in forming the hydrogeological system of the SSCP. A complicated hydrogeological system was created as a result of the developed structures that split the shallow quaternary aquifer in the research area into a number of sub-hydrogeologic zones. As a consequence, the assessment of hydro-environmental hazards is mostly based on hydro-geomorphological mapping and structural element recognition utilizing geophysical measurements and remote sensing data (El-Rayes 2004, Arnous 2016, El-Rayes et al. 2017, Arnous et al. 2016). Today, rising groundwater levels are an important component in understanding the interplay between geological structures and hydrogeological processes (López and Smith 1996; Newell et al. 1999; El-Rayes and Geriesh 2002; Bedrosian et al. 2012; Borda et al. 2022). Geo-environmental hazards might take numerous forms and are spurred on by a range of natural and human factors. However, they all have the potential to pose challenges for sociocultural evolution and dangers to public safety, individual well-being, and sustainable development goals (Arnous et al. 2011 and Culshaw 2018). Land and water are the two most crucial natural resources on the earth. Therefore, careful planning and management of these resources are extremely necessary. The main strategy for locating land degradation zones and determining the source of recharge, particularly in shallow aquifers, uses hydrogeological surveys, geophysical methods, Remote Sensing (RS), and Geographic Information System (GIS) technology (Arnous and Green 2015; Arnous et al. 2015; El-Rayes et al. 2017; Moubarak et al. 2021). Furthermore, because of the severe environmental repercussions of human and natural activities, it is vital to monitor and detect changes in land cover in order to ensure sustainable development (El-Rayes et al. 2023). This rise in water level causes several hydro-environmental consequences, including soil salinization, water pollution, water logging, and land degradation. In comparison to many conventional methods, remote sensing, GIS, and geophysical techniques have been shown to be more effective at determining how salinized soil and water logging are affected by rising water levels (Metternicht and Zinck 2003; Arnous et al. 2017; Singh 2022; Srinivasan et al. 2022). They could thus provide reasonably practical, informative, and professional rapid assessment tools for locating, monitoring, and precisely mapping structural elements, water recharge zones, land use/cover classes, and identifying the impacts of hydro-environmental hazards (Arnous et al. 2015; Geriesh et al. 2015; El-Rayes et al. 2017). Geospatial and geophysical techniques should be used to locate, assess, and map the hydro-environmental danger features. In this case, the hydrogeological and structural influencing factors were integrated using a geospatial and geo-database system. Therefore, the qualitative and quantitative hazard potentiality of each hydro-environmental feature are determined by the strength of the influencing factor and the vulnerability of the landscape (Alexander 1997; Cutter et al. 2003; Bajracharya et al. 2007; Goswami and Pant 2008; Ebert et al. 2009; Rawat et al. 2011; Arnous et al. 2011; Arnous and Green 2015; Omran et al. 2021; Arnous and Mansour 2023).

Recently, the unwise direct and indirect activities affecting the environment are endangering the SSCP. Due to the rising groundwater level induced by these activities, there were numerous hydro-environmental and soil degradation threats. Water logging and soil salinization pose the biggest obstacles to the development of urban, industrial, agricultural, and infrastructural projects. The unique feature of this study is the development of an integrated framework based on historical seismological events that utilizes many tectonic, hydro-environmental, and topo-hydrological data sets to provide a regional approach to multi-hazard exposure mapping in Rift basins.

The goal of this study is to assess the hydro-environmental hazards that threaten SSCP and to identify the main factors that influence their occurrence. The primary goal of the research is to assess the impacts of buried tectonic features on groundwater flow regime and model the hydro-environmental hazards of the SSCP. This will be accomplished by analyzing, processing, and integrating hydrogeological, geophysical, and remotely sensed data.

Study area

The SSCP is one of the worst affected by water logging, soil salinization, and land degradation in Egypt (Youssef et al. 2021, Arnous and Mansour 2023). It is located in the Egyptian Eastern Desert, near Suez City. It has a total surface area of 1632 km² and is enclosed by Longitudes 32˚22ˋ to 32˚40ˋE and Latitudes 29˚52ˋ to 30˚16ˋN. It is bordered on the north by Bitter Lakes, on the south by Suez City and G. Ataqa, on the east by Sinai, and on the west by G. Geneifa (Fig. 1).

Fig. 1

Location map A and satellite image B of the SSCP

The SSCP is classified as having a desert climate since there is primarily no annual rainfall, and the annual average temperature is 22.7 °C. May experience the driest weather because there hasn't been any rain in that month. The wettest month is November; with an average rainfall of 20 mm. January has the lowest annual average temperature (14.8 °C), while August is the warmest month. In the SSCP, the rate of evaporation generally declines toward the east, with a total annual rate of 98.5 mm. By Suez meteorological station records, the minimum relative humidity is 45.4% and the maximum is 59.9% (Abdel Basset and Hasanean 2006). For the bulk of the year, the SSCP is dominated by wind patterns from the NW, N, and NE (Suez Canal University and UNEP, 1997). The SSCP stands out because of its high wind speed on the Gulf of Suez shore, where wind speeds reach as high as 11.9 m/s.

Geology of the SSCP

The current work employs many effective processing techniques in an attempt to discriminate the rock units in the SSCP using enhanced RS data. The CONOCO geologic map of Egypt (1983) and some previous studies (Barron 1907, Hume 1925, Sadek 1926, Abdallah and Abd El-Hady 1966, and El-Akaad and Abdallah 1971), along with the enhanced satellite images, were used to generate the geological map of the SSCP (Fig. 2). Lithologically, the SSCP covered by a sedimentary succession ranging in age from Cretaceous up to Recent (Fig. 2). The Cretaceous rocks at Gabal Ataqa are composed of dolomitic and marly limestones, shales, and sandstones. The cores of Gabal (G.) Ataqa and G. Geneifa are composed of Eocene limestone and marl with thin clay laminations. The Oligocene rocks are represented by continental sands and gravels, as well as volcanic basalt sheets exposed in the G. Geneifa. The Early Miocene sediments in the Geneifa area are primarily composed of limestone, sandstone, and gypseous clay interbeds that sit uncomfortably on top of the Oligocene sand and gravel (Barakat and Aboul Ela 1971). Upper Miocene rocks are exposed in some areas of G. Geneifa, and they are primarily composed of non-marine sand sediments, sandstones, flints, pebbles, gravels, and occasionally some sandy limestones. These rocks contain some silicified wood (Abdallah and Abd El-Hady 1966). Quaternary deposits in the Isthmus Stretch's lowlands include aeolian sands, alluvium gravels with gypsum lenses, marches and sabkha deposits, and salt crust of varying thickness. Recent sediments exist in the SSCP in the form of sand dunes, limes, sands and clay deposits. Windblown sands and wadi deposits form a thin superficial layer (Fig. 2).

Fig. 2

Geological map of the SSCP created by combining interpreted enhanced TM images with the CONOCO geological map of Egypt

The exposed rock units are stratigraphically divided between pre-rift and syn-rift sequences (Strougo and Abd-Allah 1990; Sallam et al. 2015). The former is composed of Eocene rocks and can be further divided into Observatory, Qurn, wadi Garawi, and wadi Hof formations. The latter is represented by Oligocene and Miocene strata which are unconformably overlain by reworked Pliocene carbonates and Quaternary clastic deposits composed of poorly lithified sands, gravels, and quaternary alluvium (Fig. 3).

Fig. 3

Simplified stratigraphic sequence of the SSCP (adapted from Moustafa and Abd-allah 1991)

Tectonic environment of SSCP

The overall structure of the Northwestern Gulf of Suez Rift basin, comprising the SSCP, is made up of a wide horst relay zone that runs between conjugate divergent border normal faults. The key factors controlling syn-sedimentation at the northern Gulf of Suez rift are the created horst relay zones via the development and propagation of normal faults (Henaish et al. 2023). The primary fault groups WNW–ESE, ENE–WSW, E–W, NW–SE, NE-SW, and NNE-SSW are the dominant structural elements that influence and control the SSCP (Fig. 2). The E–W faults are the oldest and most likely pre-Miocene in age. The WNW–ESE faults are younger than the E–W faults and clearly affected Miocene rocks. Furthermore, the NE–SW structural fault trend is younger than the preceding two systems, and it is likely that it influenced the Quaternary sediments. Due to the drift of Arabia away from Africa, Miocene and post-Miocene extension in northern Egypt created a significant number of NW–SE oriented normal faults and rejuvenated the E–W oriented faults in the Cairo-Suez district by dextral transtension (Moustafa et al. 1998). These faults span over the basal portion of the Quaternary alluvial sediments in a similar Gulf of Suez parallel trend, indicating a recent Quaternary reactivation episode. These tendencies have been revived, according to recent seismicity data acquired over the SSCP (Fig. 4) and revealing seismic activity along the NW–SE and E–W fault lines. These faults are prevalent faults with a minor amount of strike-slip movement (Badawy 2005; Abou Elenean 2007). The Cairo-Suez district, including the SSCP, experienced active crustal deformation and volcanism during the opening of the Red Sea from the Oligocene to the Middle Miocene, resulting in deeply buried complex fault and fold structures of the Syrian-Arc System (Zain El-Din et al. 1994, and Hegazi and Omran 1998). This event is symbolized by a collection of normal faults with a N0-40W trend that are also connected to the Gulf of Suez rifting.

Fig. 4

Seismic epicenters along the SSCP from 1904 to 2017 for events with ML ≤ 4 (Compiled catalog from the International Seismological Centre (ISC), and the Egyptian National Seismic Network (ENSN), coupled with prevalent fault trends

Geomorphology of SSCP

Understanding the geomorphological setting of the SSCP is essential for the sustainable groundwater management and recognizing the hydro-environmental hazards. Hydro-geomorphological features are often utilized to characterize groundwater potential and select ideal sites for water management practices. The landscape of the SSCP is known to be greatly influenced by the tectonic activity of the Gulf of Suez Rifting as well as the climatic changes that influenced the region throughout the successive wet and dry cycles of the Pleistocene period (El-Fayoumy 1968, El-Shazly et al. 1975, Moustafa and Khalil 1994, Hussein 2001, Youssef and Abdallah 2003, Arnous 2004, El-Hefnawy et al. 2006, Arnous et al. 2011, Hagag and Obermeyer 2016).

The SSCP is primarily distinguished by a low elevation of around 1 m above sea level, but the southern and western borders are comparatively of higher relief, ranging from a few meters to the north and increase up to more than 870 m above sea level at G. Ataqa via the southwestern ward slope (Fig. 5). Few spots in the lowlands surrounding the Isthmus Stretch have very low relief down to one meter below sea level and are covered by sabkha deposits.

Fig. 5

The Digital Elevation Model (DEM) of the SSCP

A geomorphological map is produced by differentiating the main geomorphological components of the SSCP from DEM and enhanced satellite data. The SSCP has eight geomorphic components, including structural ridges, structural tableland, semi-flat terrain, isthmus length, low land with aeolian sand dunes, sand dunes belt, lakes and ponds, and Sabkha deposits (Fig. 6). The majority of the SSCP is located in the semi-flat terrain and lowlands of the El Dakruri depression. Exceptionally, a few zones of land rise up to the south at G. Ataqa (855 m), to the west at G. Geneifa (265 m), and to the northeast where sand dunes are developing (El-Fayoumy 1968, Shata and El-Fayoumy 1970, El-Shazly et al. 1975, El-Ibiary 1981, Ramadan 1984, Gereish 1989, Arnous 2004, El-Omla and Aboulela 2012, Arnous 2013, Arnous and Green 2017). The SSCP comprises several ponds, marshes, and sabkhas, but Youssif El-Sebaay Water Pond stands out since it was produced as a result of extensive agricultural developments and the application of flood irrigation techniques. Numerous wadis (dry streams) drain the SSCP, their bottoms filled with fluvio-marine sediments and alluvial deposits. The most important wadis (W) are W. Abu-Hassa, W. Nour Saloum, W. Ghali and W. El-Mr (Fig. 7).

Fig. 6

Geomorphological map of the SSCP created using enhanced satellite images

Fig. 7

Drainage map of the SSCP extracted from ASTER GDEM

Materials and methods

The current research utilizes four distinct multi-temporal Landsat 5, 7, and 8 data types to monitor and evaluate the hydro-environmental threats affecting the SSCP. ASTER GDEM was also used to create geomorphological, drainage, and groundwater flow maps. The geographic positioning system (GPS) is used for surveying and projecting the location of water points and soil samples. The USGS website (https://earthexplorer.usgs.gov) was used to download satellite data for Path P176/R39 as "Landsat 7 Enhanced Thematic Mapper" (ETM7 +) and "Landsat 8 Operational Land Imager" (OLI) dated 1984, 2000, and 2015, with spatial resolution of 30 m for pixel size. Tables 1, 2, 3 outline the overall properties of the Landsat TM, ETM + 7, and OLI data. The images encompassing the SSCP were mosaicked to provide a complete view of the investigated area, and then a subset for the area of study was extracted.

Table 1 Properties of Landsat TM data (NASA 1998)

Table 2 Properties of Landsat ETM + 7 data (NASA 2003)

Table 3 Properties of Landsat 8 (OLI) data (NASA 2013)

NASA's Terra mission launched the ASTER sensor in December 1999. It can collect stereo-image data (ASTER GDEM) with a base-to-height ratio of 0.6 by using its near-infrared spectral region and nadir-viewing and backward-viewing lenses. The horizontal plane has a spatial resolution of 15 m. The nadir-looking visual and near-infrared (VNIR) image from ASTER comprises 4100 samples by 4200 lines, which corresponds to a 60-by-60-km (km) ground region.

Remote sensing and digital image processing, which involve the manipulation and interpretation of digital images, are used to detect, map, and monitor the hydro-environmental hazards that dominate the SSCP. Layer stack, subset, geometric correction, and atmospheric corrections are all components of image pre-processing. Image processing and enhancement techniques include contrast stretching, Principal Component Analysis (PCA), band rationing, and spatial filtering. The procedure required processing the ASTER GDEM data with shaded relief at azimuth angles of 0°, 45°, 90°, and 135°, and then overlaying the outcomes of the hill shading process to enable seeing the DEM from all attainable angles. Additionally, image classification is used to define the relevant classes in the mapped area. Finally, change detection and post classification comparison techniques are used to identify differences in specific feature areas seen at various times. The rate of change is determined, and the hydro-environmental implications are assessed. ERDAS Imagine 14, ArcGIS 10.3 software were used for all operations.

Gravity and magnetic potential field geophysical techniques are used to successfully delineate both shallow and deeply buried structural features. The SSCP has a Bouguer gravity map as well as a Reduced to the Pole (RTP) magnetic map (Aero-Service 1984). The automatic processing of these maps with the proper software yielded residual and regional anomaly maps, which could recognize both shallow and deep-seated structures (Nabighian 1972; Phillips 2002). On the other hand, the electrical resistivity geophysical method has successfully been employed to delineate lithological variations in near surface sediments as well as structural features impacting subsurface sediment (Zhu et al. 2009). Vertical Electrical Soundings (VES) measurements were conducted with an Earth Resistivity Meter (PSI). The general characteristics of this device made it suitable for use in the study area (user manual). The maximum current electrode distance used in the Schlumberger array was 120 m, which is long enough to reach a depth of roughly 20 m (Zohdy 1974). When the VES is proposed with a thorough understanding of the geological, geomorphologic, and hydrogeological environments, as well as the water table conditions and topography in a specific location, accurate and reliable results have been obtained (Kavidha and Elangovan 2013; Panda et al. 2017; Kolandhavel and Ramamoorthy 2019). In SSCP, three vertical electrical soundings were performed near water logging sites. The results of the resistivity survey were used to create geoelectric sections that showed vertical and lateral variations in electrical resistivity (Zohdy 1989), allowing any faults encountered to be identified.

The hydrogeological procedures are designed in the context of the current hydrogeological conditions of SSCP. The most significant hydrogeological and morphological features are observed in the field using a range of techniques, including groundwater and surface water level monitoring, GPS-based water point mapping, and field observations (Weight 2001). Using the data gathered, the water table map of the SSCP is developed, which displays the direction of shallow groundwater flow and the sources of recharge. Generally, the flow chart summarizing the data description and the techniques employed in the current study is shown in Fig. 8.

Fig. 8

A flow chart simplifies the data description and techniques used in the current study

Results and discussion

Groundwater occurrences

The SSCP contains two major hydrogeologic environments. The first is the Quaternary aquifer, which covers the northernmost portion of the region running parallel to the Suez Canal. The second environment occupies the southern part of the research area and comprises the northern edges of the slopes that serve as the geographical extension of the northern Eastern Desert of Egypt (Fig. 6).

The Quaternary aquifer of SSCP is often semi-confined and composed of graded sand, rock fragments, and gravels with clay intercalations that occupied the semi-flat terrains of the study area (Moussa 1988, and RIGWA 1988). These clay intercalations are one of the causes of the water logging problem. The Quaternary aquifer is composed of sandstone, sand, and gravel strata at many sites of SSCP (Fig. 9). The eastern lowlands (Isthmus Stretch) of the SSCP are composed of fluvio-marine sediments (evaporatic sand facies). Regionally, the thickness of the overlying Quaternary aquifer varies as a result of faulting in the bed layers beneath.

Fig. 9

Quaternary sediment exposures consisting primarily of sand and gravel (A, B and D), with a clay layer beneath (C)

Groundwater flow behavior

The SSCP groundwater is found in Quaternary formations along the semi-flat terrain and lowlands of the El Dakruri depression and Isthmus Stretch. The Quaternary deposits formed along the semi-flat terrain and lowlands of the El Dakruri depression consist of sandstone, sand, and gravel. These deposits spread from west to east until they were crossed by the Isthmus Stretch, which is made up of fluvio-marine evaporitic sand sediments. Moreover, the Quaternary aquifer overlies directly some types of Pliocene clay and/or Miocene rocks (Fig. 9c). The Quaternary aquifer of the semi-flat terrain was in an unconfined condition. The main source of recharge to the SSCP's Quaternary aquifer is leakage from the irrigation canal system. The returned flow water from irrigation practices is another recharge source, as evidenced by water mounds along newly reclaimed irrigated lands to the west of the study area. Prior to the development of new cultivated lands, old satellite images clearly show the absence of any water ponds along the same sites (Fig. 10). Flood irrigation has a variety of effects: First, they initiate seepage processes that result in changes in pore water pressure inside the slope and seepage pressure as a result of potential transient seepage (Biniyaz et al. 2021; Guardiani et al. 2022). Second, because irrigation cycles run in flooding-drying cycles, the nearby lowlands material experiences wetting–drying cycles, which strengthens soil degradation (Miao et al. 2020; Liao et al. 2021).

Fig. 10

Early satellite image from 1984 A and more recent ones from 2015 B illustrate how water logging features have expanded before and after the development of land reclamation activities

The general hydraulic gradient of the SSCP is from the border to the Suez Canal and Bitter Lakes (Fig. 11). Because the groundwater level is higher than the sea level, the Suez Canal and Bitter Lakes act as the discharge boundary, and the groundwater flow direction is from west to both east and northeast (Fig. 11). Due to the presence of an impervious clay layer at shallow depth, the depth to the water in the east is less than 0.5 m, while in the west it is about 6 m. The poor hydraulic conductivity sediments that constitute the Quaternary aquifer in the Isthmus Stretch zone abruptly convert the contained aquifer into a semi-confined type. The aforementioned factors generate water logging, which is most noticeable close to irrigated farmland and local depressions. Because of the SSCP's high rate of evaporation, the logged water becomes more saline, and a significant amount of groundwater storage is lost due to evaporation.

Fig. 11

Water table map of the SSCP showing the groundwater flow direction

According to the remotely sensed monitoring of groundwater level signals, groundwater levels in the SSCP have gradually risen since the start of irrigated agriculture in the year 2000. Dissolved salts migrate to the shallow subsurface as water levels rise by capillary action, and when water reaches the ground surface, they cause water logging. During the evaporation of water in a dry climate, salts are left behind, degrading the soil.

Land use/land cover analysis

The enhanced multi-temporal satellite data for the years 1984, 2000, and 2015 are used to create the LU/LC distribution maps for the SSCP. Image classification, PCA, image indices, and change detection techniques were used to identify the various LU/LC classes and the possible reasons of hydro-environmental threats (Fig. 12). The generated maps show that the SSCP is vulnerable to quick and continuous changes in numerous classes of LU/LC owing to both natural and human activities. The distributions of water logging, saturated soil salinization, and vegetation cover had the most significant changes between the years 1984 and 2000 and between the years 2000 and 2015, respectively. Water-logged areas increased by 8.32 km² (0.25% to 0.90%) between 1984 and 2000, and by 2.36 km² (0.90% to 1.07%) between 2000 and 2015. Between 1984 and 2000, saturated saline soil dropped from 53.48 to 37.59 km² (4.10% to 2.91%), and from 2000 to 2015, it grew from 37.59 to 77.88 km² (2.91% to 5.98%). Vegetation expanded by 43.43 km² to 75.44 km² between 1984 and 2000 (3.33% to 5.84%), and by 75.44 km² to 231.56 km² between 2000 and 2015 (5.84% to 17.78%) (Table 4).

Fig. 12

Extracted multi-temporal LU/LC classified maps of SSCP with statistical representations of each class through the years 1984, 2000 and 2015

Table 4 Area-evaluation of the main land use land/cover classes in SSCP through the years 1984, 2000 and 2015

Furthermore, the rate of change for each LU/LC class in the research area from 1984 to 2015 is assessed (Table 5). The most important areal changes between 1984 and 2015 were in the distributions of water logging, saturated soil salinization, urban areas, and vegetation cover. The growing of water logging area (+ 10.68 km² rating + 0.35 km²/y), saturated saline soil (+ 24.40 km² rating + 0.79 km²/y), and urbanized area (+ 58.43 km² rating + 1.89 km²/y) is substantially connected with the increasing of vegetation cover (+ 188.13 km²) with an increasing rate of 6.07 km²/y. This may indicate the impact of human activities (new land cultivation and urbanization) on the dominance of hydro-environmental hazards (water logging and soil salinization) in the SSCP.

Table 5 Rates of change in areas of the LU/LC classes from 1984 to 2015 of SSCP

Geophysical analysis of morpho-tectonic anomalies

Gravity and magnetic data collected at any point on the ground surface reflect an integral impact of the fields generated by different causative sources in the vicinity of the measuring station and/or buried at various depths, as long as these sources have a sufficient physical contrast with their surroundings. The shape of the resulting anomalies is strongly influenced by the depths, sizes, and azimuths of their relevant causative sources. Short wavelength anomalies are produced by near-surface sources, while long wavelength anomalies are produced by deep sources (Tschirhart et al. 2013, Khalil 2016, Ekwok et al. 2020, Ejiga et al. 2021, Rao and Silpa 2023). As a result, by analyzing the shapes of the detected anomalies, the geometry of these sources can be deduced. These various anomalies are separated, and their depths are estimated, using the mathematical spectral analysis (Spector and Grant 1970; Kebede et al. 2021; Saada et al. 2021). This issue was addressed by using appropriate geophysical methods to locate both near-surface and deeply seated faults, which are important for figuring out the geometry of the overlying quaternary aquifer. The buried horst feature governs the geometry and thickness of the overlying quaternary aquifer, resulting in a high water level in the reservoir. As a result, the local depressions that are overlaid the horst features will be waterlogged because of the rising water level.

Airborne potential field data (gravity and magnetic) were used in this study to detect near surface and deep seated faults. Both a lateral change in the density of the subsurface rocks and variations in the Bouguer gravity values in the study area indicate the presence of faults. These faults run in three different directions: NE-SW, NW–SE, and E–W. Using the Geosoft application, the regional—residual anomaly separation procedure was applied to the Bouguer gravity map of SSCP. The regional anomaly map depicts the deep and long extension faults of the NE–SW and NW–SE trends (Fig. 13).

Fig. 13

The regional gravity map of SSCP showing the distributions of deep faults of the NE–SW and NW–SE trends

The residual gravity map of SSCP (Fig. 14) is distinguished by near-surface faults of different orientations (ENE–WSW and NW–SE) and limited extension. These faults have a significant role in the lateral and vertical movement of surface water, as well as occasionally ground water, which results in a challenge of water logging. It is important to note that several of these faults have alignments with water logging sites, which may be proof of the significant role they have in creating the structural criteria for water logging formation.

Fig. 14

The residual gravity map of SSCP showing the distributions of near-surface faults with ENE–WSW and NW–SE trends

The magnetic map can reveal the structural lineaments on the buried basement rocks and their overlying sedimentary strata. Reduced to the pole (RTP) magnetic map is always derived from the total magnetic map where the magnetic anomalies lie directly over the subsurface causative structures. The RTP magnetic map of SSCP reveals deep seated faults in the ENE–WSW and NW–SE directions (Fig. 15). Once more, these faults are the exclusive cause of some water logging sites.

Fig. 15

The RTP magnetic map of SSCP showing the distributions of near-surface faults with ENE–WSW and NW–SE trends

To identify both deep-seated and near-surface faults, the RTP map was further subjected to a regional-residual separation technique using the Geosoft software (Figs. 16 and 17). The relief of the Precambrian basement body is significantly impacted by the N–S, NE-SW, and E–W trends of the deeply seated faults (Fig. 16). Table 6 describes the deep-seated fault using information from the regional magnetic map.

Fig. 16

The regional magnetic map of SSCP showing the distributions of deep faults of the N–S, NE–SW and E–W trends

Fig. 17

The residual magnetic map of SSCP showing the distributions of near-surface faults with NW–SE and NE–SW trends

Table 6 Deeply seated fault information generated from the regional magnetic map of SSCP

The residual magnetic map of SSCP (Fig. 17) is distinguished by near-surface faults of different orientations (N–S and NW–SE). The geometry of the overlying Quaternary aquifer is controlled by the overall structural setting of the phanerozoic shallow succession, which can be determined through the identification of near-surface faults. Table 7 describes the near-surface fault using information from the residual magnetic map.

Table 7 Near-surface faults information generated from the residual magnetic map of SSCP

By using the vertical electrical sounding (VES) technology, it has been possible to better understand the subsurface geologic characteristics at several water logging sites in the SSCP. It entails injecting a high-voltage electric current into earth sediments via two current electrodes and measuring the potential difference caused by the current flow via a second set of potential electrodes. The true electrical resistivity of subsurface sediments and rock layers, as well as their depths, can be estimated using the current intensity, potential difference, and configuration factor of the used array. Using the Schlumberger Array, three vertical electrical soundings in the SSCP were measured. The current electrode distance was around 120 m, which is enough to reach a depth of roughly 20 m in the earth's layers. The three VES curves are of the 3-layer H-type (Fig. 18), and the intermediate layer of such curves has a very low resistivity value (less than 5 m), which is believed to be a layer of clay relying on the dominant surface geology. This layer prevents surface water from percolating vertically, resulting in the creation of water logging features. The presence of a low resistivity cusp in the first segment of the three curves suggests the existence of clay lenses or a lateral facies change in the surface sediment layer. The bottom layer has a relatively high resistivity and is thought to be a fractured limestone layer based on the SSCP's geology. This layer is highly fractured and could serve as a drain to help mitigate the water logging challenge.

Fig. 18

VES curves at the study area showing cusps, H-type and second layer with very low resistivity (clay layer)

The geological cross-sections (Figs. 19 and 20) drawn across the three VES curves revealed that the second geoelectric layer (Clay layer), which has a very low resistivity, acts as a barrier to prevent vertical percolation of the surface water, that leads to the formation of water logging features. This layer is also influenced by faults, which can act as conduits for surface water to flow downward into the underlying fractured limestone aquifer. This approach might be regarded as a potential water logging mitigation strategy.

Fig. 19

A geological cross-section of the SW–NE profile shows how tectonic features affect the thickness of the overlaid Quaternary aquifer (see Fig. 16 for deep faults & Fig. 17 for near surface faults locations)

Fig. 20

A geological cross-section of the NW–SE profile shows how tectonic features affect the thickness of the overlaid Quaternary aquifer (see Fig. 16 for deep faults & Fig. 17 for near surface faults locations)

The influence of morphotectonics on groundwater flow regime

The faulting, folding, and fractures of bedrock aquifers and their confining layers, which result in varying geometry and hydraulic properties, can have a significant impact on groundwater flow (Spottke et al. 2005; DesRoches et al. 2014; El-Rayes et al. 2017, 2020; Moore and Walsh 2021). Faults have a massive effect on groundwater flow in the Quaternary aquifer of the SSCP. The geometry of the buried graben and horst features caused by major tectonic rifting of the Gulf of Suez has a significant effect on the flow pattern and thickness of the overlaid shallow Quaternary aquifer in the SSCP (Figs. 19 and 20). The buried horst influences the geometry of the top quaternary aquifer, causing aquifer thickness to thin and groundwater levels to rise, resulting in water logging.

The groundwater flow direction in the Quaternary aquifer is guided by the clay layer topped horst beneath it. When groundwater recharged and circulating in the Quaternary aquifer reaches the depth of the impermeable clay-capped horst, it is directed in part towards the east (to the Suez Canal) and the northeast (to the Bitter Lakes) (Fig. 11). Actually, the position of the groundwater level is defined by this clay-capped horst, which may be raised above the ground surface, resulting in the formation of water logging features, particularly at topographic depressions.

The influence of morphotectonics on the vulnerability to hydro-hazards

Water logging and soil salinization, caused by recent human activities at the SSCP, are now the most prevalent desertification phenomena, endangering soil fertility and causing significant water loss through evaporation. The prevailing morphological and tectonic evolution of the enclosed area has a strong influence on aquifer thickness (Rubio et al. 2007). The thickness of the Quaternary aquifer that lies on top of the buried horst structures is closely connected with the distribution of water logging sites along the SSCP (Fig. 19). The most vulnerable area to water logging and, as a consequence, soil salinization is the thin water-bearing formation zone that lies above the buried horst structure at the recharge zone (Fig. 19). The rapid recharge rate of seepage from irrigation systems and the excess irrigation water returned-flow from the recently reclaimed cultivated lands both contribute to the development of water logging at the recharge zone of SSCP. The graben faulting created a sedimentary basin filled with thick sediments that serves as a groundwater reservoir zone at the lowlands discharge border (Fig. 20).

The dynamic pattern of water logging development

The analysis of satellite images and field observations revealed that significant tracts of water logging and water ponds had formed on the low land surfaces as a result of the cultivation of broad regions in semi-flat terrains bordered by low lands. The majority of the water logged spots are dispersed in a distinct pattern that resembles local topographic depressions and thin top-soil layer. Because of the prevailing aridity, most of the western semi-flat topography has weak surface expression and is presently covered by thin Quaternary gravely sands underlain by a shallow Pliocene clay layer. The extent of seepage and water logging within the newly cultivated fields in the SSCP coincides with the automatically retrieved surface slope from the DEM. Excess irrigation water seeps through the subsurface and progressively migrates towards the lowland along the Isthmus Stretch, saturating the dormant local depressions. This significant correlation strongly suggests the influence of geomorphology and landforms on the dynamics of water logging. Local depressions focus the seepage down the surface slope via the lowlands eastward, resulting in the development of surface ponds in distant cultivated lowlands. The entire agricultural area in the SSCP was roughly 43 km² in 1984, and it expanded to 232 km² in 2015. During the same time span, waterlogged and ponded spots expanded from around 3.3 km² to nearly 14 km². The present study clearly demonstrates that development has not considered the regional physiographic setting of soil, hydrological environment, and geomorphology of agricultural regions. The agricultural fields in the SSCP are primarily planted on semi-flat topography landforms. The majority of the soils in these landforms are thin (less than 0.5 m thick), governed by structural setting, and underlain by an impervious clay layer. This means that the clay layer underneath these soils may obstruct the vertical flow of groundwater, facilitating the rapid development of water logging problems.

Conclusion

The SSCP identifies significant site impacts of the Gulf of Suez rifting as buried graben and horst structures. The resulting tectonic structures in SSCP govern the local groundwater flow regime and the hydrogeologic zonation of the overlying Quaternary aquifer. A first key step in explaining the groundwater flow regime and associated hydro-environmental hazards that prevailing in the study area is the identification of buried bedrock geometry and lateral variations in the thickness of the overlying Quaternary aquifer.

The groundwater discharge zone in the western portion of SSCP is distinguished by significant tectonic features, particularly the buried graben structures. The water table measurement revealed significant water level variations all over the eastern part of the SSCP, which was highlighted by the graben structure. This variation indicates that the graben structure serves as a basin for groundwater accumulation at the discharge area's end of the flow path.

The local groundwater flow in the overlying Quaternary aquifer originated at the western recharge boundary, directly above the buried horst-graben structure, and became directed into the eastern lowlands and northeastern Bitter Lakes. At the western recharge zone of the SSCP, the aquifer is primarily recharged by seepage from new irrigation distributaries as well as returned-flow water from excessive irrigation water in newly reclaimed lands.

The thickness of the Quaternary aquifer overlying the buried horst structure is strongly correlated with the distribution of waterlogged sites and soil salinized zones in the SSCP. Thick water-bearing formation controlled by graben structure receives a large volume of accumulated groundwater at the discharge area on the eastern border, causing the groundwater level to rise above the ground surface, resulting in the development of water logging features. The thin water-bearing formation overlying the buried horst structure at the recharge area to the western border is the most vulnerable to water logging and, as a consequence, soil salinization.

There are significant gaps in scientific understanding of the environmental consequences of tectonic rift basins. The current study adds to closing some knowledge gaps by better understanding the impact of rift-related structures on the susceptibility to hydro-environmental hazards. Because rift basin environment concepts are still in the early stages of study, there is no data on environmental effects are available. Mitigation and restoration of ecosystems are effective in reducing the effects of hydro-environmental hazards on soil of rift basins, which needs to be researched more in the near future.