Identification of geomorphic signatures of active tectonics in the Wadi Hagul Basin, Northwest Gulf of Suez, Egypt: insights from SRTM derived geomorphic indices and watershed analysis

The satellite data, include Landsat 7 Enhanced Thematic Mapper (ETM+), Landsat-8 (OLI), Shuttle Radar Topography Mission (SRTM), were processed and interpreted for creating an integrated geospatial map of the geomorphic indices (GI) of Wadi Hagul Basin (WHB). The present study is considered new, useful, and valuable in northwest of Gulf of Suez region to evaluate active tectonics using SRTM resulting drainage network and GI. Where fairly slight studies on active tectonics recognized on GI were prepared in the investigated area. The GI includes; Ratio of valley floor width to valley height (Vf), Transverse topographic symmetry factor (T), Stream length-gradient index (SL), Drainage basin shape (Bs), hypsometric integral (Hi), geomorphological landform and watershed analysis. Also, GI were integrated and combined with the seismic and structural lineaments intensities maps to create an integrated single index map. The morphotectonic geo-spatial distribution hazards map reveals that the high risky area is 82.75% of the total area, the moderate-risk area is 16.51%, and the low risky morph-tectonic area is 0.81%. Based on this map, it is necessary for planners and decision makers to extremely study attractive applicable action concerning the recommended mitigation measurements from this study to avoid any serious future problems in WHB and its surroundings areas.


Introduction
Currently, the northwestern area of the Gulf of Suez province, which is the most important investment area in Egypt, has many sustainable development projects considerably contributes to the national income (El-Rayes et al. 2009;Arnous and Green 2011;Arnous and Mansour 2023;Hegazi et al. 2023).Hence, the investigation of the natural geologic and environmental hazards, especially active tectonics are vital in urban planning and development.
Active tectonics are processes responsible for producing deformation of the earth's crust on a time scale of significance to human society and are valuable tools in natural hazard assessment (Keller and Pinter 2002).
The identification of the geomorphic signatures of tectonic activity studies, which are used to evaluate the active tectonics, should be based on geomorphic indices (GI).These GI include ratio of valley floor width to valley height (V f ), stream length-gradient index (SL), transverse topographic symmetry factor (T), hypsometric integral (Hi), drainage basin shape (B s ), mountain front sinuosity (S mf ) and basin asymmetry factor (A f ).The indices not only provide evidence about regional tectonic deformation of an area, but also its level of tectonic activity (Keller 1986;Keller and Pinter 1996).Moreover, the data acquisition frequently can be collected certainly from SRTM and Aster GDEM as space-borne data.

The study area
The Wadi Hagul Basin (WHB) is bounded by latitudes 29° 41 ' and 30° 01 ' N, and longitudes 32° 08 ' and 32° 24 ' E. It occupies an area of about 375 Km 2 and basin perimeter is about 131.28 km (Fig. 1).It lies at the North Western part of the Gulf of Suez between G. Ataqa (870 m), and El-Galala El-Baharia Plateau (1260 m) (Fig. 2).It is accessible through the Suez-Hurgada Highway, and Cairo-Sokhna Highway.The WHB is surrounded by such landscape as G. EL-Kahiylia and G. Abu Trifya, W. Beda and W. Ghweiba, which are draining eastward to the Gulf of Suez.
WHB area is distinguished by desert-like climatic conditions, dominated by long, hot and dry summers, and mild winters (Arnous et al. 2011).During winter seasons, WHB is subjected to occasional storms of heavy showers producing flash floods having catastrophic effect on the industrial zone located at the downstream reaches of the basin.The stratigraphy of the WHB area has been studied in detail by several authors, e.g., Sadek 1926;Said 1962;Youssef et al. 1970;Ismail et al. 1974;Abdallah 1993 andAlmoazamy 2018.The main channel of W. Hagul occupies nearly the middle of the depression, which extends for about 35 km and collects running water both sides.It is covered by soft rocks ranged in age from Eocene to Quaternary and drained by four main drainage systems namely W. Umm Ramath, W. Umm Rishat, W. Umm Zeita and W. Abu Sili.The wadi upstream engraves its course into soft marls and grits beds of the Upper Eocene rocks.The main wadi is trending southeast cutting the limestone beds of the Miocene age.The wadi downstream is widening and cuts its course across Quaternary deposits.The Quaternary alluvial deposits consist of coarse gravels in the upper reaches, while at the down streams it is becoming rougher and rich in large boulders of limestone.

Materials and methods
The satellite data used in this study, include Landsat 7 Enhanced Thematic Mapper (ETM+), Landsat-8 (OLI), Shuttle Radar Topography Mission (SRTM).These data were processed and interpreted using several software, such as ERDAS Imagine 2014, ARC-GIS 10.4.1, SAGA-GIS 2.1.2,Q-GIS 2.18 and Global Mapper 18. Shuttle Radar Topography Mission (SRTM) images were produced and give details until 90 m spatial lengths, and hence, used to make DEM, contour, and relief map, as well as, to extract drainage networks.The data are available internationally at 90 m horizontal resolution and 16 m vertical accuracy with 90% confidence level (Rodríguez et al. 2006).These data were chosen and used, for the capability of the C-band wavelength (5.7 cm) in penetrating the superficial sand layer and revealing the near-surface paleo-drainage networks.Buried features often leave subtle topographic traces on the surface, which are visible on DEMs of very high vertical accuracy and spatial resolution.So, they can be enhanced by artificially illuminating the surface to create a shaded relief (Evans 2007).In addition to, the DEM is unremitting because voids have been filled by interpolation procedures, and it is used for regional scale geomorphic analysis (Grohmann et al. 2007).
Therefore, the SRTM elevation data is employed to visualize the differences in topography through several methods of terrain analyses such as longitudinal and traverse profiles, slope, contour elevation maps, 3D perspective views, and the GI.Moreover, a 3D perspective view is helpful for the In the current work, geomorphic indices (GI) are employed for analyzing landforms and evaluating the tectonic activity degree of Wadi Hagul Basin (WHB).The quantitative measurements and geomorphic indices are extracted using the digital elevation model (SRTM) as follows:

Ratio of valley floor width to valley height (V f )
The ratio of the valley floor width to its height (V f ratio), It is calculated as follows: Where: V f is the ratio of the valley width to valley floor; (1)

Stream length-gradient index (S L )
The stream length-gradient index (S L ) indicates the role of rock resistance (resistant against erosion) in streams, and it is computed by the equation (Hack 1973): Where: S L is the stream length gradient index; ΔΗ/ΔL is the stream gradient at a specific reach (point) in the channel, (ΔΗ) is the change in elevation of the reach, ΔL is the length of the reach), and L is the channel length from the divide to the midpoint of the channel reach for which the index is calculated.

Transverse topographic symmetry factor (T)
The transverse topographic symmetry factor evaluates the amount and the variation of asymmetry of a river or wadi course within specific basin.It is calculated regarding the larger axis of the basin.This factor (T) is the ratio of the distance from the basin midline to the active meander-belt midline (D a ) and to the basin divide (D d ).The basin midline would be the location of a river that is symmetrically placed regarding the basin divide.The factor (T) is calculated as follows (Keller and Pinter 2002):

Hypsometry integral (H i )
Generally, hypsometry is the measurement of land elevation relative to sea level.In other words, it represents the relationship between elevation and basin area, watershed, or catchment (Strahler 1952).Hypsometric Curve and Hypsometric index (H i ) can be created through the analysis of hypsometry.This curve is constructed by plotting the proportion of the total basin height (h/H = relative height) versus the total basin area (a/A = relative area).
Total basin height H represents the relief within the basin (i.e., the difference between the maximum and minimum elevations in the basin).Total surface area of the basin (A) is the sum of the areas between each pair of adjacent contour lines.Total basin area (a) represents the surface area within the basin above a given line of elevation h (Keller and Pinter 2002). (2) The shape of the hypsometric curves is related to the degree of dissection of the basin; a convex-upward curve indicates a young stage, a sigmoidal curve indicates a mature stage, and a concave-upward curve indicates a senile stage (Keller and Pinter 2002;Guarnieri and Pirrotta 2008).
The hypsometric integral (Hi), or area elevation analysis (Strahler 1952), is a quantitative measure of the degree of dissection of a drainage basin and reflecting the state of landscape evolution.
The hypsometric integral (Hi) is calculated by using the following equation (Pike and Wilson 1971): Where: H i is the hypsometric integral; h max , h min , and h mean are the maximum, the minimum, and the mean elevation, respectively.

Drainage basin shape (Bs)
Drainage basin is the area that encompasses all the land from which water flows into a particular stream or river.The area of a drainage basin may vary from a few square kilometers to a part of a continent.The horizontal projection of the basin shape may be described by the basin shape index or the elongation ratio, (B s ) (Ramirez-Herrera 1998) and can be calculated as follows: Where: B l : is the length of the basin measured from the headwater to the month and B w : is basin width in the widest point of the basin.
In the present work, the integration of geologic, structural, seismic, and GI data that were statistically treatment and mapped based on the weighted linear combination method.It is one of the most commonly used multi-criteria decision-making technology (Afshari et al. 2010;Arnous 2013, 2016and Arnous et al. 2020).The morphotectonic integrated model of WHB is mostly dependent on the concept of the simple multiplication of the criteria scores with the pre-assigned weights of obtained thematic data.In which the overall scores for all geodatabases were estimated and the parameter with the highly score is preferred.The created thematic maps were categorized and scored into different factors that are controlled in the tectonic activity then integrated to generate the spatial model of the morphotectonic risky zones of the WHB (Table 1).

Results and discussion
In the present study, the analyses, and interpretations of SRTM DEM data revealed significant information on the geomorphology and geometry of Wadi Hagul Basin (WHB) (4) which are problematic to be identified through other spaceborne satellite data.

Drainage network and geomorphological landforms
The drainage network pattern and hydrographic characteristics of WHB which are extracted from the SRTM using Arc hydrology tools in ArcGIS environment is shown in Fig. 3. From the hydrographic point of view, WHB occupies an area of about 275km 2 , and the main catchment covers the area between the Ridges of Um Zeita and Akheider to the south and Ataqa Cuesta to the north (see Fig. 2).WHB has a large areal extension and has a sixth order trunk.It is drained by four main drainage systems namely W. Um Zeita, W. Abu Sili, W. Umm Rishat and W. Umm Ramath.It drains with drainage gradient of about 18.51 m/km southeastward to the Gulf of Suez and has a relief ration 24.79.The trellis drainage pattern is the predominant one, which has a common drainage direction with a secondary direction parallel to it (NW-SE), so that primary tributaries join main streams at right angles (NE-SW) and secondary tributaries run parallel to the main streams (NW-SE).At the study area, this pattern is associated with alternating dipping hard and soft sedimentary rocks, definitely the ridges of Um Zeita and Akheider and Ataqa Cuesta are present.Obviously, the main wadis of WHB are structurally controlled, where they engraved their courses along NW-trending faults which are related to the famous Gulf of Suez Rift.
From the geomorphological point of view, WHB is a depression which is bounded from the north by Ataqa Cuesta and from the west by Kahaliya -Umm Zeita Ridge (see Fig. 2).The upper part of Hagul depression lies within a graben trending NW Upper in the middle Eocene limestone.The northeastern fault represents the Ataqa scarp, whereas the southwestern fault is the Kahaliya-Umm Zeita ridge (Fig. 4).

Active tectonic and geomorphic indices
The GI of hydrographic basins of the study area are discussed in the following sections:

Ratio of valley floor width to valley height (V f )
The plotted transverse profiles across WHB are shown in Fig. 5, whereas the extracted topographic profiles are shown in Figs. 6 and 7.Moreover, the derived parameters are listed in (Table 2).V f index was calculated for WHB area based on Eq. ( 1), and its spatial distribution map is shown in Fig. 8.As it is well-known, the V f parameter distinguishes U-shaped valleys from the V-shaped ones,  The Vf values of the study area range from 10.29 to 0.97 and grouped into three classes (Fig. 8).The majority of the WHB is assigned moderate rate (1 < V f >5), followed by low rate (V f >5) at the downstream of the WHB.The low V f values (0.97), indicating high rate of activity along the 3a -3b profile in the northwestern part of WHB.So, most of WHB displays a slow level of uplift and valleys with flat floor and U-shaped, whereas it displays a high rate of uplift and along one of the deep V-shaped valleys at one profile (3a-3b), which could be attributed to uplift associated with incision process.

Stream length-gradient index (S L )
The S L index may reveal the relationships between tectonic activity, rock resistance against erosion and topography as a result of the influence of sudden changes in channel slope.Large differences in S L , and any changes in the longitudinal profile of a stream may discover zones of tectonic activity.
All the data required for computing the (S L ) index are measured from the topographic profiles, are illustrated in Fig. 9.The length (L) is measured along the main stream from the divide to the midpoint of the processed segment (Fig. 10).Finally, the calculated (S L ) of each section of the principal stream is assigned at the midpoint of the section (Table 3).
The WHB main stream and along with the longitudinal profile are shown in Fig. 10.Also, the calculated stream length-gradient index (S L ) is listed in Table 3, and the spatial distribution map of (S L ) index is illustrated in Fig. 11.
The (S L ) values range between 48.07692 and 234.2857 and are grouped into three classes (Fig. 11).The S L index values increase as streams flow is crossing over active uplifts and may have lesser values when flowing parallel to normal faults or grabens (Keller and Pinter 2002), such conditions are encountered in WHB, where the main stream is running parallel to NW-trending Gulf of Suez faults, whereas as at the perturbation sites, the Sl values  abnormally increase.Several locations along the main stream show anomalous (S L ) values, especially at a distance 4-6 km from the upstream of the main Hagul, where it is crossing very conspicuous right-lateral slip shear zone (see Fig. 10).

Transverse topographic symmetry factor (T)
The calculated values of transverse topographic symmetry factor (T) of WHB area are listed in Table 4, and profiles and their spatial distribution are displayed in Figs. 12 and 40 Page 12 of 20 13.All of the calculated (T) values in WHB are less than 0.1 (0.006782-0.32847),indicating less tilting.This can be attributed to that the main stream is running along a NW-trending graben, which is more or less symmetrical in geometry.parallel to the major fault which depicts the valley.The zero (T) value represent a minimum which indicates perfect asymmetric basin, whereas T = 1, is a maximum and represents asymmetric basin or a tilted one (Keller and Pinter 2002).

Hypsometry integral (Hi)
In the current study, the (Hi) is estimated using the digital elevation model (DEM) of the Hagul basin.
The calculated (Hi) values are listed in Table 5 indicate that the geological stage of WHB is the mature stage with the least degree of convexity and the watershed is poorly susceptible to erosional impact over tectonics and produce dissected drainage basins.
If, H i ≤ 0.3 (old stage), it means watershed is fully stabilized, and if, 0.3 ≤ Hi ≤ 0.6 indicate watershed is susceptible to erosion (equilibrium or mature stage).And finally, if, H i ≥ 0.6 (non-equilibrium or young stage) indicate watershed is highly susceptible to erosion (Keller and Pinter 2002).The calculated H i value of WHB is 0.403 (i.e., 0.3 ≤ Hi ≤ 0.6); which means that the main basin is in the maturity stage, and the landscapes characterized by low relief contrasts.Moreover, the value reveals higher erosional impact over tectonics and produce dissected drainage basins.

Drainage basin shape (Bs)
Based on the estimation of the (Bs) values; the elongated basins are associated with high values of (Bs), which in turn associated with relatively higher tectonic activity.While the low values of (Bs) indicate a more circular-shaped basin, generally associated with low tectonic activity.
In the present study, the calculations of drainage basin shape (B s ) are listed in Table 5, and the spatial distribution map of (B s ), which was prepared by using geospatial tools of GIS is displayed in (Fig. 14)., the (Bs) value is 2.6 (i.e., < 3), indicating slightly higher longitudinal shape, i.e., slightly high tectonically active area than other wadis at the northwest of Gulf of Suez.

The morphotectonic hazard map of Wadi Hagul Basin (WHB)
The morphotectonic geo-spatial distribution hazards map of Wadi Hagul Basin (WHB) is produced based on the integration of the main five GI thematic maps; V f , S L , T, H i , and B s maps, as well as the seismic magnitude and structural lineament intensities thematic maps.The integration is achieved by using a linear combination of these factors in an ArcGIS spatial analysis environment to create an integrated single index map.The resulted morphotectonic geo-spatial distribution hazards map (Fig. 15) is classified into three categories from high to low risky areas of relative tectonic activity.The numerous geo-spatial thematic maps as described in the preceding have been transformed into raster form.These were then reclassified and assigned suitable weights (Table 1).
1 3 40 Page 14 of 20 Fig. 12 The transverse topographic profiles of Wadi Hagul Basin (WHB) The high risky areas occupied about 82.75% of the total area which represents southern scarps of G. Ataqa and El-Kahaliya -Umm Zeita ridge.In which the upper part of WHB course lies amongst upper Eocene rocks of Maadi Formation, which area faulted down between two scarps of middle limestones, the easterly scarp being bounded by one of G. Ataqa NNW-SSE faults and the west by a similar fault in G. Kahaliya (Fig. 16).The central part and the downstream of WHB are characterized by moderate-risk area, represent about 16.51% the total area.While about 0.81% of the total area is represented the low risky morph-tectonic area occupied in the boarders of WHB area.
Although methods, calculations, and interpretations of active GI are applied systematically in the current study, there are some contrast and signs in our analyses and interpretations reflect that GI are not completely going with each other hand by hand.That may provide the planners and decision makers by pseudo geospatial results about the morph-tectonic of WHB.Such as, the low Vf values indicating high rate of activity along the 3a -3b profile in the northwest of WHB only.Whereas, some previous works (revealed that the WHB area is still active by major faults.Also, H i indicate that the geological stage of WHB area in mature stage with the least degree of convexity and the watershed is poorly susceptible to erosional impact over tectonics and produce dissected drainage basins.In addition, most of the measurements of (T) values in WHB are indicating less tilting.This can be attributed to that the main Hagul stream is running parallel to the major fault which depicts the valley.Hence, these contrasted results could be explained based on the following:  Many NNW and NW oriented oblique slip normal faults are recorded at the southwestern flank of G. Ataqa parallel to sub-parallel to WHB (Fig. 17).The NNW oriented normal faults end against the en-echelon fault belts like those mapped by Moustafa et al. (1985).On the other hand, the NW oriented faults do not end against the en-echelon fault belts; rather, they joined or linked by them.The en-echelon fault belts act as transfer zones which transfer the throw from one NW oriented fault to another.In addition, along W. Hommath, parallel to the east of WHB a set of minor faults lines striking NNW are encountered and starting with maximum throw at the edge of the scarp and gradually decreases towards downstream.Furthermore, WHB considered as tectonic depression bordered by the southern scarps of G. Ataqa and the El-Kahaliya-Umm Zeitia Ridge (Fig. 17).The upper part of stream lies amongst upper Eocene rocks Maadi Formation, which are faulted down between two scarps of middle Eocene limestones, the easterly scarp being bounded by one of the G. Ataqa NNW-trending faults and the west by a similar fault in Gabal Kahaliya.The geological cross section which is demonstrating these NW-trending faults that is bounding the basin is shown in Fig. 18.The Hagul fault is running in the middle part, which is a mega structural lineament extending from the tip of the Gulf of Suez until the border zone of the River Nile (Moretti and Gargani 2008).
The GI site selection is in the same conditions of geological and geomorphological setting, as it is worldwide, which gives results that may contradicts with the actual tectonic activity of WHB.Hence, to avoid any pseudo results of interpretations of GI data, the profiles must be taken perpendicular to the main stream and the active faults.Where any changes occurring along the longitudinal profile of a stream reflect possible tectonic influences.From the geospatial integrated results point of view, it is necessary for planners and decision makers to extremely study attractive applicable action concerning the recommended mitigation measurements from this study to avoid any serious future problems in WHB and its surroundings areas.
Therefore, our recommendations for the researchers to carry out image processing and good analyses of the space-borne data and field observations before applying the GIS tools in determination of the GI of investigated area.These will support in revealing the evidence of the presence of active tectonics that depend mainly on the deflected streams, deformed landforms, active mountain fronts and triangular facets.

Summary and conclusion
The Wadi Hagul Basin (WHB) lies at the North Western part of the Gulf of Suez between G. Ataqa, and El-Galala El-Baharia Plateau.The main approach of the present study is to use previously tested techniques such as RS, GIS and GI, that have been in various tectonically active areas around the world.The study aims at identifying, computing, assessing and mapping the numerous GI related to active tectonics and topographic development, and creating an integrated single index map, which can be used to distinguish the relative active tectonic signatures exploiting RS.
The satellite data used in this study, include Landsat 7 Enhanced Thematic Mapper (ETM+), Landsat-8 (OLI), Shuttle Radar Topography Mission (SRTM).These data were processed and interpreted using several software, such as ERDAS Imagine 2014, ARC-GIS 10.4.1, SAGA-GIS 2.1.2,Q-GIS 2.18 and Global Mapper 18. Shuttle Radar Topography Mission (SRTM) images were produced and give details until 90 m spatial lengths, and hence, used to make DEM, contour, and relief map, as well as, to extract drainage networks.Moreover, a 3D perspective view was applied to provide perspective views of the terrain, and to sharpen the topography, particularly for cases where the topographic data and optical images are integrated.
From the hydrographic point of view, WHB occupies an area of about 275km 2 , and the main catchment covers the area between the Ridges of Um Zeita and Akheider to the south and Ataqa Cuesta to the north.From the geomorphological point of view, WHB is a depression which is bounded from the north by Ataqa Cuesta and from the west by Kahaliya -Umm Zeita Ridge.Based on V f values, the majority of the WHB is Several locations along the main stream show anomalous (S L ) values, especially at a distance 4-6 km from the upstream of the main Hagul, where it is crossing very conspicuous right-lateral slip shear zone.
All of the calculated (T) values indicating that WHB has less tilting (< 0.1), which can be attributed to that the main stream is running along a NW-trending graben.The calculated H i value (0.403); which means that the main basin is in the maturity stage, and the landscapes characterized by low relief contrasts.Moreover, the value reveals higher erosional impact over tectonics and produce dissected drainage basins.The (Bs) value is 2.6, indicating slightly higher longitudinal shape, i.e., slightly high tectonically active area than other wadis at the northwest of Gulf of Suez.
The morphotectonic geo-spatial distribution hazards map of Wadi Hagul Basin reveals that the high risky areas occupied about 82.75% of the total area which represents southern scarps of G. Ataqa and El-Kahaliya -Umm Zeita ridge.The central part and the downstream of WHB are characterized by moderate-risk area, represent about 16.51% of the total area.While about 0.81% of the total area is represented the low risky morph-tectonic area occupied in the boarders of WHB area.
Although methods, calculations, and interpretations of active GI are applied systematically in the current study, there are some contrast and signs in our analyses and interpretations reflect that GI are not completely going with each other hand by hand.That may provide the planners and decision makers by pseudo geospatial results about the morph-tectonic of WHB.Hence, to avoid such pseudo results, the profiles must be taken perpendicular to the main stream and the active faults.Where any changes occurring along the longitudinal profile of a stream reflect possible tectonic influences.
Finally, the gained results considered vital information for decision makers of the Ministry of Housing and Construction, Cairo and Suez governorates.Consequently, it is necessary for future effective mitigation measures of the morph-tectonic geohazards, to assess, manage, and plan for sustainable development activities.Concerning the Northwestern Gulf of Suez region and new urban areas.

Fig. 3 Fig. 4
Fig. 3 The drainage network of the main basins and sub-basins in Wadi Hagul Basin (WHB)

Fig. 9
Fig. 9 Diagram showing the measurements of Stream length gradient index (S L ) along Main stream of Wadi Hagul Basin (WHB)

Fig. 11
Fig. 11 Map showing the spatial distribution map of Stream-Length-gradient index (S L ) of Wadi Hagul Basin (WHB)

Fig. 13
Fig. 13 Map showing the spatial distribution of transverse topographic symmetry factor (T) of Wadi Hagul Basin (WHB)

Fig. 14
Fig. 14 Map showing the spatial distribution Drainage basin shape (B s ) index of Wadi Hagul Basin (WHB)

Table 1
Thematic map weight and their geomorphic capability values of Wadi Hagul Basin (WHB) area

Table 2
Calculations of the Ratio of valley floor width to valley height (V f ) of Wadi Hagul Basin (WHB) area

Table 3
Calculations of the Stream length-gradient index (S L ) of WHB

Table 4
Calculations of transverse topographic symmetry factor(T) of Wadi Hagul Basin (WHB)

Table 5
Calculations of the hypsometric integral (H i ) and Drainage basin shape (B s ) values of Wadi Hagul Basin (WHB)