Proposing the Optimum Withdrawing Scenarios to Provide the Western Coastal Area of Port Said, Egypt, with Sufﬁcient Groundwater with Less Salinity

: Recently, groundwater resources in Egypt have become one of the important sources to meet human needs and activities, especially in coastal areas such as the western area of Port Said, where seawater desalination cannot be used due to the problem of oil spill and the reliance upon groundwater resources. Thus, the purpose of the study is the sustainable management of the groundwater resources in the coastal aquifer entailing groundwater abstraction. In this regard, the Visual MODFLOW and SEAWAT codes were used to simulate groundwater ﬂow and seawater intrusion in the study area for 50 years (from 2018 to 2068) to predict the drawdown, as well as the salinity distribution due to the pumping of the wells on the groundwater coastal aquifer based on ﬁeld investigation data and numerical modelling. Different well scenarios were used, such as the change in well abstraction rate, the different numbers of abstraction wells, the spacing between the abstraction wells and the change in screen depth in abstraction. The recommended scenarios were selected after comparing the predicted drawdown and salinity results for each scenario to minimize the seawater intrusion and preserve these resources from degradation.


Introduction
Water scarcity has recently become an important problem, especially in arid and semiarid areas such as Egypt [1]. The continuing need for water due to the population increase in Egypt has led to an increase in the use of groundwater resources, since these needs are not being met by surface water sources [2]. Population growth increases the water requirements leading to increased pumping of the aquifers [3]. Therefore, groundwater is considered an important natural resource and the main source of water supply in many coastal regions [4]. In such regions, groundwater resources are over-exploited to meet the development and urbanization of coastal zones and the excessive pumping of groundwater in coastal aquifers has reduced the freshwater flux to the sea and allowed seawater to migrate inland [5].
The western area of Port Said is one of the coastal regions located in the north of Egypt, northeast of the Nile Delta, where the increase in population and human needs has resulted watershed [60], covers an area of about 23.5 km 2 and is characterized by mild topography, as it does not exceed 5 meters above sea level, either to the north and south where the Mediterranean Sea and Manzala Lake are 0 and less than 0 meters, respectively. The main geomorphic units along the study area are the coastal sand dunes, which are concentrated on the north side of the study area (on the coast), and the sabkha, which is concentrated in the southern part in the direction of Manzala [61].

The Study Area
The study area is located 150 m south of the Mediterranean coast in the northeast of the Nile Delta and west of Port Said, Egypt ( Figure 1a). As shown in Figure 1b, c, it extends between the latitudes of 31°21′ to 31°21′12″ east and longitudes of 32°4′57″to 32°5′18″ north. The study area belongs to the northeastern part downstream of the Nile watershed [60], covers an area of about 23.5 km 2 and is characterized by mild topography, as it does not exceed 5 meters above sea level, either to the north and south where the Mediterranean Sea and Manzala Lake are 0 and less than 0 meters, respectively. The main geomorphic units along the study area are the coastal sand dunes, which are concentrated on the north side of the study area (on the coast), and the sabkha, which is concentrated in the southern part in the direction of Manzala [61].

Meteorological Data of the Study Area
The study area is located in an arid climate region; the average daily temperature varies between 17 • C and 20 • C at the Mediterranean Sea coast [62]. The annual mean values for relative humidity in the morning and the evening are between 60% and 80%, respectively [4]. The highest average monthly rainfall in the study area is 50 mm in November ( Figure 2a) and the highest average annual rainfall amount in the last 12 years was about 64 mm in 2015 (Figure 2b). The average values of the surface evaporation and evapotranspiration are about 180 mm/year and 126 mm/year, respectively, in the study area [63]. Due to the high evaporation rates and limited precipitation in the study area, local rainfall provides negligible replenishment of groundwater [2,60]. The analysis of the time series of rainfall during the period 2009-2021 ( Figure 2b) led us to conclude that rainfall will not notably change and will not contribute to the aquifer within the study area. Therefore, it is ignored.

Meteorological Data of the Study Area
The study area is located in an arid climate region; the average daily temperature varies between 17 °C and 20 °C at the Mediterranean Sea coast [62]. The annual mean values for relative humidity in the morning and the evening are between 60% and 80%, respectively [4]. The highest average monthly rainfall in the study area is 50 mm in November ( Figure 2a) and the highest average annual rainfall amount in the last 12 years was about 64 mm in 2015 (Figure 2b). The average values of the surface evaporation and evapotranspiration are about 180 mm/year and 126 mm/year, respectively, in the study area [63]. Due to the high evaporation rates and limited precipitation in the study area, local rainfall provides negligible replenishment of groundwater [2,60]. The analysis of the time series of rainfall during the period 2009-2021 ( Figure 2b) led us to conclude that rainfall will not notably change and will not contribute to the aquifer within the study area. Therefore, it is ignored.

Geological Setting
Generally, two main geological components in the ND region are Quaternary deposits and Tertiary deposits [65]. The Quaternary includes the Holocene and Pleistocene sediments. Holocene deposits are widely spread with a maximum thickness of about 77 m [66].
Moreover, the thickness of Quaternary deposits increases in a northward direction to reach 250 m in the south and 1000 m in the north [67].
The study area clearly consists of quaternary deposits [65]. These deposits are gravel and sand with some clay lenses belonging to Bilqas, Mit Ghamr and Wastany formations from the Holocene and Pleistocene periods.

Hydrogeological Setting
Hydro-geologically, these quaternary strata are very important with a significantly amount of water stored. According to well data, the groundwater aquifer system is classified into three aquifers (unconfined, leaky and deep), which have about 90 m, 200 m and 400 m thickness, respectively. Figure 3a shows the subsurface geological cross-sections in (Figure 3b) and around the study area ( Figure 4). Five test wells are located in the study area to carry out full hydrogeological studies of the aquifer, rely upon the groundwater of the aquifer and desalinate it to improve its quality. The static water levels in the five wells within the study area were measured and indicated that the shallow wells (GW 01 and GW 05) range from −1.4 to −0.9 m and from −1.4 to −1.1 m, respectively, while the groundwater levels for the deep wells (GW 02, GW 03 and GW 04) range from 0.6 to 1 m, from 0.8 to 1.1 m and from 0.5 to 0.8, respectively. The aquifers' salinities were monitored and the hydraulic parameters of the aquifers were estimated through pumping tests of wells.

Geological Setting
Generally, two main geological components in the ND region are Quaternary deposits and Tertiary deposits [65]. The Quaternary includes the Holocene and Pleistocene sediments. Holocene deposits are widely spread with a maximum thickness of about 77 m [66]. Moreover, the thickness of Quaternary deposits increases in a northward direction to reach 250 m in the south and 1000 m in the north [67].
The study area clearly consists of quaternary deposits [65]. These deposits are gravel and sand with some clay lenses belonging to Bilqas, Mit Ghamr and Wastany formations from the Holocene and Pleistocene periods.

Hydrogeological Setting
Hydro-geologically, these quaternary strata are very important with a significantly amount of water stored. According to well data, the groundwater aquifer system is classified into three aquifers (unconfined, leaky and deep), which have about 90 m, 200 m and 400 m thickness, respectively. Figure 3a shows the subsurface geological cross-sections in (Figure 3b) and around the study area ( Figure 4). Five test wells are located in the study area to carry out full hydrogeological studies of the aquifer, rely upon the groundwater of the aquifer and desalinate it to improve its quality. The static water levels in the five wells within the study area were measured and indicated that the shallow wells (GW 01 and GW 05) range from −1.4 to −0.9 m and from −1.4 to −1.1 m, respectively, while the groundwater levels for the deep wells (GW 02, GW 03 and GW 04) range from 0.6 to 1 m, from 0.8 to 1.1 m and from 0.5 to 0.8, respectively. The aquifers' salinities were monitored and the hydraulic parameters of the aquifers were estimated through pumping tests of wells.

Methodology
Groundwater modeling is the most widely used method for understanding the flow regime of groundwater aquifers, as well as for assessing the amount of water that will be used to know the potential of the aquifer and the effect of seawater intrusion due to over-pumping.
To achieve the research objectives, field data were collected to identify the hydraulic properties and salinity of the aquifer. Groundwater flow and solute transport (seawater intrusion) were simulated using the MODFLOW and SEAWAT codes and the testing scenarios were developed to simulate flow and transport in the western Port Said coastal area for 50 years (from 2018 to 2068) to predict the drawdown as well as the salinity distribution due to the pumping of the wells on the groundwater coastal aquifer according to the methodology in Figure 5. This study defined the characteristics of the aquifer system and the baseline salinity of the coastal aquifer using field data and a numerical model. Eighteen scenarios were developed to minimize the effect of seawater intrusion on the Nile Delta aquifer within the study area. The simulation results were compared to the initial salinity values (baseline condition) in the aquifer at the control points, which indicated a change in the different scenarios. • Sc e.1: total pumping of 50,000 m 3 /day; • Sc e.2: total pumping of 100,000 m 3 /day; • Sc e.3: total pumping of 150,000 m 3 /day.
These criteria for the scenarios (the change in well abstraction rate, the different numbers of abstraction wells, the spacing between the abstraction wells and the change in screen depth in abstraction wells) were taken into consideration as the requirements for the desalination plant. For example, the quantities of discharge were determined for what this plant would meet in terms of the quantities of water required to be used. In addition, the locations of the proposed wells were determined in accordance with the available places in the study area, taking into account the distances between wells and engineering constructions. The comparison of the scenarios was made using five observation points to observe aquifer salinity. The best and most appropriate scenario is the scenario with the lowest predicted salinity concentrations. The hydrogeological conceptual model was developed to describe the site hydrogeological conditions. The flow conceptual model was built based on the findings of field investigations and the geological and hydrogeological characteristics of the subsurface layers, while the transport conceptual model describes the transport of seawater and parameters of concern to the groundwater aquifers and, especially, into the abstraction wells.  The scenarios were utilized to predict future responses of the aquifer using the following principles:

•
The change in well abstraction rate; • The different numbers of abstraction wells; • The spacing between the abstraction wells; • The change in screen depth in the abstraction wells.
As mentioned in Figure 2b, there are five of wells in the study area on which the above-mentioned scenarios of the 2018 (steady state condition)-2068 projection were based; the different scenarios for each arrangement of the wells are discussed as follows: a.
The first arrangement of the wells (Figure 6a) consists of five wells located in the northern part of the study area being used with two screen depths (unconfined aquifer and leaky confined aquifer); for each screen depth, different well abstraction rates are considered: • Sc e.1: total pumping of 50,000 m 3 /day; • Sc e.2: total pumping of 100,000 m 3 /day; • Sc e.3: total pumping of 150,000 m 3 /day.
These criteria for the scenarios (the change in well abstraction rate, the different numbers of abstraction wells, the spacing between the abstraction wells and the change in screen depth in abstraction wells) were taken into consideration as the requirements for the desalination plant. For example, the quantities of discharge were determined for what this plant would meet in terms of the quantities of water required to be used. In addition, the locations of the proposed wells were determined in accordance with the available places in the study area, taking into account the distances between wells and engineering constructions. The comparison of the scenarios was made using five observation points to observe aquifer salinity. The best and most appropriate scenario is the scenario with the lowest predicted salinity concentrations. The hydrogeological conceptual model was developed to describe the site hydrogeological conditions. The flow conceptual model was built based on the findings of field investigations and the geological and hydrogeological characteristics of the subsurface Water 2021, 13, 3359 9 of 21 layers, while the transport conceptual model describes the transport of seawater and parameters of concern to the groundwater aquifers and, especially, into the abstraction wells.

Model Geometry
The numerical model of the study area was carried out using a mesh of 48 rows and 48 columns with an area of about 23.5 km 2 , as shown in Figure 7, in which the aquifer system defined in the conceptual model is composed of three aquifers: the first unit is unconfined shallow aquifer A, which belongs to the quaternary age, with an average thickness of 90 m; the second unit is leaky confined aquifer B, which belongs to the Mit Ghamr formation of the Pleistocene age, with an average thickness of 200 m; the third unit is confined deep aquifer C, which belongs to the Wastany formation of the upper Pleistocene age, with an average thickness of 200 m. There are two layers of clay with a thickness of about 20 meters; the first separates the shallow aquifer and the leaky aquifer B, while the other separates the aquifers B and C. All aquifers consist of sand and gravel with intercalated clay lenses.

Model Geometry
The numerical model of the study area was carried out using a mesh of 48 rows and 48 columns with an area of about 23.5 km 2 , as shown in Figure 7, in which the aquifer system defined in the conceptual model is composed of three aquifers: the first unit is unconfined shallow aquifer A, which belongs to the quaternary age, with an average thickness of 90 m; the second unit is leaky confined aquifer B, which belongs to the Mit Ghamr formation of the Pleistocene age, with an average thickness of 200 m; the third unit is confined deep aquifer C, which belongs to the Wastany formation of the upper Pleistocene age, with an average thickness of 200 m. There are two layers of clay with a thickness of about 20 meters; the first separates the shallow aquifer and the leaky aquifer B, while the other separates the aquifers B and C. All aquifers consist of sand and gravel with intercalated clay lenses.

Boundary Condition
The hydrogeological boundary conditions were selected according to water level data from drilled wells and the hydrogeological map of the Nile Delta aquifer [1], as follows:

Boundary Condition
The hydrogeological boundary conditions were selected according to water level data from drilled wells and the hydrogeological map of the Nile Delta aquifer [1], as follows: 1.
Northern boundary: Mediterranean Sea representing the northern constant head and constant salinity concentration (40,600 mg/L), according to water analysis. 2.
Southern boundary: Manzala Lake representing the southern constant head with a -3 value and constant salinity concentration (50,760 mg/L), according to water analysis.

Hydrogeological Parameters
To identify the hydraulic properties of the aquifer, pumping tests were conducted on the five exploratory wells. After completion of well construction and development, step and continuous pumping tests were performed on each well.
Pumping tests were conducted in two wells in aquifer A (GW 01 and GW 05), in three wells in aquifer B (GW 02, GW 03 and GW 04) and reviewed from previous works [18,42,68].
According to the pumping test analysis, the transmissivity value ranges were determined as follows: • The Boulton 1963, Hantush 1960 and Thesis 1935 pumping test analysis methods [69][70][71] were used to estimate the hydraulic properties (transmissivity and storativity of pumped aquifer; vertical hydraulic conductivity and storage coefficient of aquitard) of unconfined, leaky confined (semi-confined) and confined deep aquifers, respectively (Figure 8).

Model Calibration
Boundary conditions, hydraulic properties and initial conditions are classic prerequisite parameters for the aquifer domain and the accuracy of the final output is highly dependent on these parameters [2], especially when simulating groundwater flow in such The results show that the values of hydraulic conductivity of unconfined sandstone ranging from 13 to 28 m/day were obtained from the pumping tests of two wells (GW 01 and GW 05), while the values of hydraulic conductivity of confined sandstone ranging from 4 to 11 m/day were obtained from the pumping tests of two wells (GW 02 and GW 03) and the values of horizontal hydraulic conductivity of confined deeper sandstone ranging from 3 to 5.5 m/day were obtained from the pumping tests of the GW 04 well. The vertical hydraulic conductivity value is one-tenth of the value of horizontal hydraulic conductivity [72].

Model Calibration
Boundary conditions, hydraulic properties and initial conditions are classic prerequisite parameters for the aquifer domain and the accuracy of the final output is highly dependent on these parameters [2], especially when simulating groundwater flow in such heterogeneous media [73]. To achieve an accurate simulation, the spatial distribution of the aquifer hydraulic properties conditioned with physical measurement (e.g., hydraulic conductivity, porosity, storativity and dispersivity) should be determined [73].
The model was calibrated by trial and error by changing the hydraulic parameters and the calculated water levels and comparing them with the measured levels. Hydraulic conductivity was used as a calibration parameter. In model calibration, trial-and-error approaches were used to manually match the field and simulated data. A sensitivity analysis was conducted on hydraulic conductivity and porosity. The hydraulic conductivity ranged from 3 to 28 m/d and the porosity ranged from 0.2 to 0.45. The parameter of sensitivity was evaluated using the root mean square error (RMSE) method, which demonstrated that the model was sensitive to hydraulic conductivity but insensitive to porosity for the test range.
Regarding field data, the model was calibrated using 2018 field data. The year 2018 was chosen as the calibration year to calibrate the model under equilibrium (steady state) conditions. Figure 9 shows the groundwater flow in the study area where the flow direction gradually decreases from the Mediterranean Sea in the north to Manzala Lake in the south. The model was calibrated until the lowest possible error values were reached for five observation points and the results show that the residual varied between 0.098 m (GW 03) and 0.67 m (GW 01) with a root mean square (RMS) of 0.362 m and a normalization root mean square of 9.675%, as shown in Figure 10a.
The computed water budget consists of two parts, inflow and outflow. In the model studied, the inflow budget included one component, inflow across boundaries, while the outflow budget consisted of two components, outflow across boundaries and groundwater withdraw of wells, which was 0 m 3 /day in a steady state but changes according to discharge rates in the transient state of the model and is used in domestic and water supply. Table 2 shows that the calculated total inflow was 89,910.4297 m 3 /day and the total outflow was 89,919.2109 m 3 /day with a net flow of about 9 m 3 /day, which indicates that the discrepancy percentage was 0.01%.

Groundwater Flow Model
Groundwater flow and solute transport (seawater intrusion) were simulated under transient conditions for a prediction period using the MODFLOW and SEAWAT codes for 50 years (18,250 days), from 2018 to 2068, to predict the drawdown in groundwater levels and changes in groundwater salinity as a result of extraction scenarios. The stress period of the calibration run was set to one year (365 days). The prediction period was divided into 50 stress periods.  The SEWAT code was calibrated using the existing salinity field data of 2018. The three main aquifers were simulated to study the effect of seawater intrusion. The initial conditions of TDS in the three aquifers were assigned according to the water samples analysis and the results of the EC logs. Seawater salinity was 40,600 mg/L TDS. For aquifer A, TDS was 32,410 mg/L. Aquifer B was divided into three sub-layers with salinities of 21,000 mg/L, 25,000 mg/L and 33,000 mg/L, respectively. Salinity of aquifer C ranged between 50,000 mg/L and 60,000 mg/L. This aquifer was divided into two sub-layers and the sensitivity analysis was performed to predict the impact of this bottom aquifer on the salinity of abstracted water.
Longitudinal dispersivity was used as a calibration parameter. Figure 10b shows the calibration curve between the field and simulated salinity values in 2018 for three observation points.

Groundwater Flow Model
Groundwater flow and solute transport (seawater intrusion) were simulated under transient conditions for a prediction period using the MODFLOW and SEAWAT codes for 50 years (18,250 days), from 2018 to 2068, to predict the drawdown in groundwater levels and changes in groundwater salinity as a result of extraction scenarios. The stress period of the calibration run was set to one year (365 days). The prediction period was divided into 50 stress periods. Table 3 and Figure 11 explain the results of predicted drawdown in 18 scenarios as follows:

•
The first three scenarios (Sc a.1, Sc a.2

Simulation of Saltwater Intrusion
Here, the scenarios relative to future changes in seawater due to over-pumping of groundwater resources in the study area are discussed. Figures 12 and 13 show the predicted curves of salinity concentrations for 18 scenarios at one control point (GW 02).
Based on the results of the salinity of the monitoring well from the results of the representation of water salinity and the test of sea interference with groundwater, the following become clear:

•
According to scenarios Sc a.1, Sc a.2 and Sc a.3 (Figure 12a), which refer to extraction from the first aquifer, over time, the salinity of the water would reach about 40,000 mg/L when the largest amount is extracted, which is 150,000 m 3 /day; however, these scenarios were excluded because they required studying the effect of the extraction of this amount of groundwater on the facilities, foundations and infrastructure of the station, as well as on the nearby facilities. According to scenarios Sc a.4, Sc a.5 and Sc a.6 (Figure 12a`), in which extraction is performed from the second aquifer, with wells located at a distance of about 165 m from the sea, the salinity would range from 38,000 to 40,000 mg/L.

Simulation of Saltwater Intrusion
Here, the scenarios relative to future changes in seawater due to over-pumping of groundwater resources in the study area are discussed. Figures 12 and 13 show the predicted curves of salinity concentrations for 18 scenarios at one control point (GW 02).
Based on the results of the salinity of the monitoring well from the results of the representation of water salinity and the test of sea interference with groundwater, the following become clear:

•
According to scenarios Sc a.1, Sc a.2 and Sc a.3 (Figure 12a), which refer to extraction from the first aquifer, over time, the salinity of the water would reach about 40,000 mg/L when the largest amount is extracted, which is 150,000 m 3 /day; however, these scenarios were excluded because they required studying the effect of the extraction of this amount of groundwater on the facilities, foundations and infrastructure of the station, as well as on the nearby facilities. According to scenarios Sc a.4, Sc a.5 and Sc a.6 (Figure 12a'), in which extraction is performed from the second aquifer, with wells located at a distance of about 165 m from the sea, the salinity would range from 38,000 to 40,000 mg/L.

Conclusions
This study presents the sustainable management of groundwater resources in the coastal aquifer at the western area of Port Said, Egypt, due to human expansion activity in this area. The main objective is proposing the optimum withdrawing scenarios to provide the study area, with sufficient groundwater with less salinity. In this regard, a groundwater model was developed. The Visual MODFLOW and SEAWAT codes were

Conclusions
This study presents the sustainable management of groundwater resources in the coastal aquifer at the western area of Port Said, Egypt, due to human expansion activity in this area. The main objective is proposing the optimum withdrawing scenarios to provide the study area, with sufficient groundwater with less salinity. In this regard, a groundwater model was developed. The Visual MODFLOW and SEAWAT codes were used in the study area to simulate, over 50 years (from 2018 to 2068), groundwater flow and groundwater salinity and predict the drawdown and, consequently, the impact of seawater intrusion according to the testing scenarios. The eighteen testing scenarios included the change in well abstraction rate, the different numbers of abstraction wells, the spacing between the abstraction wells and the change in screen depth in the abstraction wells. After comparing, the results recommend the groundwater abstraction to be performed from aquifer B and, preferably, a time of 25 years in the scenarios Sc b.1, Sc b.2, Sc c.1, Sc c.2, Sc d.1 and Sc d.2 to minimize the highest values of drawdown and salinity concentration due to seawater intrusion. The average value of salinity would be about 35,000 mg/L if the groundwater abstraction was used in the quantities illustrated in the recommended scenarios in a shorter period of time, such as 25 years, in order to obtain a sufficient and permanent source of water required to be utilized as a main source of water. On the other hand, taking into consideration the groundwater salinity, this would achieve the goal of sustainable development of renewable resources such as groundwater.