1. Introduction
Coastal lakes within the coastal zone of Egypt act as multi-functions for the surrounding environment and local people. These lakes are sensitive to a group of stressors which include reclamation for alternative uses, hydrological modifications, pollution, and erosion [
1]. In Egypt, as a country characterized by water scarcity, increasing water demands, and different development activities, such as agriculture, have affected many ecosystems across the coastal zones of Egypt during the last century [
2]. As populations grow and economic development proceeds through the twenty-first century, human-induced pressures on aquatic resources in the already heavily populated coastal zone will increase [
3]. Furthermore, climate change will have negative impacts on water resources and sea level rise [
4,
5]. In fact, monitoring and modeling ecosystem functions is an important prerequisite for developing management policies for coastal lagoons in Egypt.
In fact, hydrology is the principal driving factor of the environmental role of wetland ecosystems. In this context, the importance of initiating a hydrological database represents the core role for hydrological and environmental studies for all wetlands, including coastal lagoons and shallow lakes [
6,
7].
Hydrological processes depend on meteorological circumstances. These include the water resources of direct precipitation and water loss by evaporation. Any changes in the balance between precipitation and evaporation influence seasonal changes in lagoons’ hydrological environment.
At the lateral boundaries of coastal lagoons in Egypt, hydrological conditions are controlled by freshwater discharged into the lagoon and water exchange between the lagoons and the sea. Water exchange is influenced by two factors. The first is the difference between water levels in both the sea and the lagoon. The second is the type of the connection between the sea and the lagoon.
Regarding the lagoons’ catchment area, freshwater resources represent a major factor in the inflow term of the water budget of the lagoon. In many cases, as in Egypt, coastal lagoons receive freshwater from groundwater aquifers. In fact, freshwater inflows into the lagoon impact lagoons’ water quality, in particular, water salinity [
8,
9]. In addition, freshwater inflows provide coastal lagoons with nutrients and sediment. In fact, hydrological processes are the main source of nutrient supply within coastal lagoons [
10]. The continuous freshwater inflows, coupled with seasonal the difference between precipitation and evaporation magnitudes, result in spatial and temporal variability in lagoons’ water levels, salinity, and nutrient status [
11].
Both quantities and qualities of freshwater inflows into the lagoons and lakes are largely influenced by the catchment area size, its geology, and its climate [
12]. Human activities within the coastal lagoons’ catchment areas have a direct impact on the magnitude and the quality of freshwater inflows [
13]. Human activities that influence lagoons’ water quality are the direct result of water resources management within the catchment area [
14].
Like other coastal lagoons, Al Bardawil Lagoon is subjected to different anthropogenic activities, such as the mega land reclamation project in Northern Sinai and El-Salam canal. Seepage from both irrigation and drainage waters through the soil of loose sand will affect the water quality of the lake and eventually end up in the aquifer beneath the lake and its catchment area. Domestic wastes of the new settlements in the vicinity of the project will be added to agricultural wastes and pollutants and will undoubtedly alter the environmental picture of the region. In addition, the limited amount of rainfall in the region and shoreline changes can have a profound effect on the geomorphology of the lagoon. These circumstances enhanced the need to assess Al Bardawil Lagoon hydrological characteristics to set the hydrological baseline for future changes expected due to ongoing human activities and agricultural developments planned in the lagoon’s vicinity.
The meteorological factors were investigated to assess the hydrological characteristics of the lagoon. Historical rainfall records, evaporation loss measurements, water level fluctuation data were collected and analyzed. Meteorological data were statistically analyzed, and the water resources of the lagoon were estimated. Water losses and outflows were assessed. The lagoon bathymetry and wind action were investigated. Furthermore, the water balance of the lagoon’s hydrology system was defined by implementing the water budget procedure. In addition, a field program was implemented to record the water table for a period of three months in the year 2004.
2. Study Area
Al Bardawil Lagoon is located on the northern coast of the Sinai, Egypt. It extends from 32°41′00″ to 33°30′00″ E longitude and from 31°03′00″ to 31°14′00″ N latitude. It has a surface area of 650 square kilometer with a total length of 80 km and a maximum width of 14 km. The lagoon is a shallow water body with an average depth of 1 m,
Figure 1. The Mediterranean Sea borders the lagoon from the north. The lagoon is bordered by a sand dune belt from the south while the Al-Arish-Rafah sector presents its eastern border, and the Al Tinah plain represents its western border. The bottom of the lagoon is composed of sand and silt.
A long sand bar separates the lagoon and the Mediterranean Sea. The lagoon contains the Al Zaranik protectorate area in the eastern section. Al Zaranik area represents the most east section of Al Bardawil Lagoon with a length of about 30 km. It hosts the Al Nasr salt production company. On the other hand, the western part of the Al Bardawil Lagoon has a length of about 80 km [
15].
The Al Bardawil Lagoon has six habitats, including open water, wet salt marshes, saline sand flats and hummock (nebkas), stabilized sand dunes, inter-dune depressions, and mobile sand dunes [
16]. It receives the migrating birds as well as the Al Zaranik area. Fishing and salt production are the main economic activities in the lagoon. It contains many ecosystems of habitat. It is the least polluted lagoon within the Mediterranean coastal lagoons. The lagoon is connected to the sea by three inlets.
Al Bardawil Lagoon has Mediterranean weather with low water temperature in the winter season and high temperature in the summer season. Many development projects are carried out within the lagoon vicinity. The North Sinai agriculture development project is the largest project under execution in the area,
Figure 2. It is expected that the seepage of agriculture water used in the project will deteriorate the lagoon’s water quality and will alter the salinity of the lake water from hypersaline to a brackish environment.
The site provides an important spawning area for fish, supports commercially important fish populations, and is an important wintering and staging area for about 500,000 birds. Considerable ecological changes have occurred due to the extension of salt extraction and the constant formation of sand bars (siltation), which close the channels connecting the lagoon to the sea.
Like all coastal lagoons in Egypt, the Al Bardawil Lagoon has many challenges which might result in environmental retreating. The most effective challenge is the changes that takes place in its inlets due to sedimentation processes and sediment transport along its coastline. This process results in decreasing the fishing activities as the fishing boots face transportation problems between the sea and the lagoon. Additionally, the expected water quality deterioration would result in changing the lagoon ecosystems.
4. Results and Analysis
4.1. Wind Speed and Direction
Results of wind speed and direction data revealed that the dominant wind direction is NW with values around 4.5 m/s. The area experienced a few strong storms that had speed values greater than 10 m/s associated with W and SW winds. Previous studies concluded that NW winds that blow in the afternoon have strong magnitudes that vary between 6 and 7 m/s, and those that blow in the evening have low values of about 2 m/s [
22]. Fortunately, these winds do not contribute to wave action as they blow offshore on the Mediterranean coast,
Figure 13.
The seasonal variation in the wind shows stronger winds blow in March in the winter season with a maximum monthly mean value of 4.9 m/s and weaker winds with a minimum monthly mean magnitude of 3.7 m/s blow in August during the summer season.
4.2. Water Resources of the Lagoon (Inflow)
Study results revealed that water resources are rainfall, groundwater, and water inflows from the Mediterranean Sea through the lagoon openings.
4.2.1. Rainfall
Rainfall analysis revealed that water resources are rainfall, groundwater, and water inflows from the Mediterranean Sea through the lagoon openings. The rainfall analysis showed that the study area received 94.5 mm per year. This amount of rainfall contributed about 61.95 million cubic meters to the lagoon’s hydrologic balance,
Table 9. Furthermore, the analysis revealed that most rainfall takes place in the winter season while the summer season has no rainfall. In this respect, rainfall analysis proved that 70% of the rainfall takes place in four months (December through March).
4.2.2. Groundwater Inflow/Outflow
Hydrological studies analysis manifested that groundwater in the sand dune aquifer system moves toward the north. This means that the dune system supplies the lagoon with a fraction of its water resources. The analysis demonstrated that the dune system provides the hydrological balance of the lagoon with a daily volume of 24,000 m3. This rate contributes as much as 0.72 million m3/month and about 8.64 million cubic meter per year.
4.3. Outflows from the Lagoon
4.3.1. Salt Production Requirements
The Al Nasr Company for Salt Production discharges about 250 million cubic meters of water from the lagoon to its salting basins. This volume was divided over the year according to the monthly evaporation rate. Accordingly, that volume was divided as presented in
Table 10.
4.3.2. Evaporation Losses
Evaporation losses from the lagoon were estimated for each month. The average monthly losses depth was transformed to monthly losses volume by considering the lagoon surface area (650 km
2),
Table 11. Analysis revealed that the lagoon experiences annual evaporation losses of about 1155.05 million cubic meters.
Figure 14 illustrates the monthly rainfall volumes, salt production requirements, and evaporation losses from the lagoon.
4.3.3. Al Bardawil Lagoon Water Balance
The water balance procedure was implemented to assess the interaction between the Al Bardawil Lagoon and the sea. The water balance is a systematic method for quantifying the hydrologic components within a specified hydrologic system. It includes all the major inflows and outflows of water within the hydrologic boundaries of the lagoon system. This procedure was applied to assess the values of unknown elements of the hydrologic system, such as the changes in the lagoon storage and the rate of outflow from the lagoon.
The water budget was defined through the continuity equation as follows:
In which
ds/
dt is the storage change rate within a specified time interval. Inflow is the water discharged into the lagoon. Outflow includes the water losses from the hydrologic system and water interaction between the lagoon and the sea.
The Inflow term in the equation includes monthly rainfall and groundwater quantities. On the other hand, the Outflow term includes monthly evaporation losses and water required for salt production. Water balance results are shown in
Table 12,
Figure 15. Results of the water balance of the Al Bardawil Lagoon indicated the following:
Annual rainfall provides the lagoon with 4.4% of its annual inflow.
Groundwater provides the lagoon with 0.6% of its annual inflow.
Annual inflow volume is about 70.59 million cubic meters.
Annual evaporation losses account for 82.2% of its total annual outflow.
Annual water discharged from the lagoon for salt production represents about 17.8% of the water outflow from the system.
The outflow term from the lagoon is 1405.05 million cubic meters annually.
The difference between inflow and outflow is 1334.46 million cubic meters annually. This volume is replenished by Mediterranean Sea water.
Results presented in the table showed that the monthly outflow (evaporation + salt production requirements) is always greater than the monthly inflow (rainfall and groundwater). Accordingly, water moves from the sea to the lake every month to replenish the monthly difference. This is the reason for the negative sign in the ds/dt column in the Table. This process resulted in a continuous movement of seawater into the lagoon, with discharges varying from 27.2 to 54.3 m3/s. In addition, this process keeps water level in the lagoon below mean sea level with values range between 11 and 21 cm.
Table 12.
Water balance of the Al Bardawil Lagoon.
Table 12.
Water balance of the Al Bardawil Lagoon.
Month | Inflow | Outflow | Storage Change (ds/dt) | Water Level (cm) | Inflow from the Sea to the Lagoon (m3/s) |
---|
Rainfall (106 m3) | Groundwater (106 m3) | Salt Production Requirements (106 m3) | Evaporation (106 m3) | Inflow–Outflow (106 m3) |
---|
January | 14.95 | 0.72 | 15.33 | 70.85 | −70.51 | −11 | 27.2029 |
February | 9.1 | 0.72 | 15.9 | 73.45 | −79.53 | −12 | 30.6829 |
March | 7.475 | 0.72 | 19.415 | 89.7 | −100.92 | −16 | 38.9352 |
April | 5.2 | 0.72 | 20.68 | 95.55 | −110.31 | −17 | 42.5579 |
May | 1.625 | 0.72 | 22.65 | 104.65 | −124.955 | −19 | 48.2079 |
June | 0 | 0.72 | 23.49 | 108.55 | −131.32 | −20 | 50.6636 |
July | 0 | 0.72 | 25.18 | 116.35 | −140.81 | −22 | 54.3248 |
August | 0 | 0.72 | 24.76 | 114.4 | −138.44 | −21 | 53.4105 |
September | 1.5 | 0.72 | 23.22 | 107.25 | −128.24 | −20 | 49.4753 |
October | 4.55 | 0.72 | 22.09 | 102.05 | −118.87 | −18 | 45.8603 |
November | 5.2 | 0.72 | 19.415 | 89.7 | −103.195 | −16 | 39.8129 |
December | 12.35 | 0.72 | 17.87 | 82.35 | −87.35 | −13 | 33.6998 |
Total | 61.95 | 8.64 | 250 | 1155.05 | −1334.46 | | |
% | 4.4% | 0.6% | 17.8% | 82.2% | 95% | | |
Figure 15.
Water Balance of the Al Bardawil Lagoon.
Figure 15.
Water Balance of the Al Bardawil Lagoon.
4.4. Water Table Fluctuation
The water table was recorded on a daily basis at 6 am and 6 pm for the period (21 August until 21 November 2004). Assuming that the water table in the lagoon has the same level as seawater at the beginning of the observation program, the first reading at each site was considered as zero sea water level.
Although the observation period was insufficient to draw concrete conclusions about water table fluctuation, the difference between the average maximum and the average minimum values of the water table for the observation period agreed to some extent with water balance results,
Table 13. Comparing water table in
Table 12 and
Table 13 demonstrated that the water table fluctuation resulted from the water balance procedure for the months August through November ranged from 18 to 21 cm below sea level with a mean value of 19.5 cm, while the average value of water fluctuation for the five observation sites varying between 19.5 and 24.5 with an average value of 22 cm.
Although the difference between the results of observed data and water balance was small, the difference is attributed to the short observation period while the water balance results were drawn from long-term records of historical data. In addition, wave action-induced windstorms and fishing boat activities have a direct influence on water surface fluctuation.
For more analysis,
Table 14 demonstrates the maximum difference between the first reading at each site (assumed as zero water level) and water table fluctuation. From the results illustrated in the Table, the following could be concluded.
Maximum water table fluctuation changed from one site to another. During the observation period, the maximum water table was raised above mean sea level with magnitudes reaching up to 18.5 cm. On the other hand, the minimum water table had levels less than the mean sea level, with values ranging from 12 to 27.5 cm.
The fluctuation ranges were within the tide range (30 cm). The fluctuation of the water table included all factors that affect this process, such as wind action, boat movements, tide action, and storage change due to the net evaporation and salt production requirements. The maximum water table above sea level is due to wind and tide actions, while the maximum fluctuation below sea level is mainly attributed according to storage change which is the difference between monthly inflow and outflow.
Study results defined the main components of the lagoon hydrological system. It presents the baseline for the hydrological status of the lagoon. This baseline could be used by the local and governmental authorities to monitor and assess any changes in the hydrological status of the lagoon due to human and tourism activities as well as the agricultural development projects in the vicinity of the lagoon. Accordingly, a hydrological monitoring system is recommended to assess any changes in the water table, groundwater quality as well as any other hydrological parameters.