The hydrogeological condition of Dibdibba aquifer between Karbala and Najaf in the middle of Iraq

The study area is located on the Dibdibba plateau in the middle of Iraq, particularly between the governorates of Karbala and Najaf. Given that the Dibdibba hydrogeological aquifer is thought to be the main source of water in this region, this site is chosen for performing the hydrogeological assessment. The study included 60 wells located on the west of the study area in Najaf Governorate. In these wells, the groundwater depths were measured in the field at the beginning of December 2021. The water stream was between 7.8 and 37.7 meters above the sea level, while the well depths ranged from 2.83 to 34 meters. Then, the spatial distribution of depths and water streams was mapped. Many wells were left by farmers because the water stream had gone down and the depth of the water had increased. The flow net of groundwater was determined to have two directions. The first direction was from the west to the east


Introduction
The last 60 years have seen unprecedented groundwater extraction and overdraft in all of the world [1].By 2025, 1.4 billion people in about 48 countries will suffer from the water scarcity [2].Iraq is going through an unprecedented severe water crisis for many reasons, including climate changes, lack of rain, and the policies of neighboring countries, in addition to the increase in requests due to the population growth [3].The study area is located to the East of the Western Desert and includes 1114 square kilometers between Karbala in the north and Najaf in the south, along the Euphrates River in the west, within longitudes (43°90 -44°25 ) and latitudes (31°95 -32°40).Its interior and the exposed geological formations are of Tertiary and Quaternary age (middle Eocene-Pleistocene).They are listed from the oldest to the newest: Dammam, Euphrates, Fat'ha, Injana, and Dibdibba [4].
Hydrogeologically, the study area is located within Mesopotamia and the Western Desert Zone, and the main aquifers of groundwater are Miocene carbonate and Mesopotamian plain silt [5] (see Fig. 1).The Dibdibba aquifer is the main aquifer in the study area.Since the population has grown on both sides of the road between Karbala and Najaf, it has also reduced the rate of groundwater recharge due to the change of the basin or watershed from natural land to an urban area.For this reason, the area requires studies and continuous monitoring of groundwater levels due to such processes as over-pumping, pollution, little recharge, and re-evaluation of developments in it.
The study objectives include identifying the hydraulic head of groundwater in the Dibdibba aquifer, the sources of its recharge, as well as the direction of flow, and estimating the hydraulic parameter by pumping-test experiments and data analysis, thus determining the aquifer's natural drainage.The study area gradually elevates above the sea level as it flows from the west to the east.According to the data from DEM-30 and the US Geological Survey, its height is between 12 and 90 meters above the sea level (Fig. 2)

Methodology:
In this study, (60) wells from different locations in the area studied were monitored and the groundwater depth was measured by a sounder device, and then the spatial distribution of depths was drawn.After that, the water stream was determined by subtracting the depths of water from the elevation taken from a digital elevation model of the USGS (DEM-30) and dropped from the global mapper program because it was more accurate than the readings taken in the field by GPS.The spatial distribution of the water stream (a.s.l.meters) was drawn.In addition, the direction of groundwater movement was determined and crossed vertically with the water stream in order to draw the flow net.The hydraulic gradient was calculated according to Darcy's law in the northern, southern, and middle parts of the study area.The hydraulic properties of the Dibdibba aquifer were calculated by conducting five pumping experiments distributed in the study area and analyzing the data using Neuman's and Jacob's correct methods for the unconfined aquifer.
Many software applications were used to process and analyze the data as follows: 1.A location map of the research region was created with highlighting the location of wells.Then, a map of the test pumping wells' position, and spatial distribution maps for water dept, water level, hydraulic gra dient, and flow net) was created using the ArcGIS software.2. The Global Mapper (22.1) was used for the corrected elevations by projecting well points on the Digital Elevation Model (DEM-30).3. Aquifer Test (2011.1)was used to analyze the pumping test data with observing wells (multi-well), because it gave accurate analysis in this way in (PW1) (Fig. 8).4. AQTESOLV was used to analyze the pumping test data of single-well pumping because of its high accuracy.

Results and Discussion
The values of water depths in the study area ranged between 2.83 and 34 meters below the earth's surface.The shallow depth was located in the eastern and northeastern regions, most possibly as a result of artificial groundwater recharge by the human activities in the suburban areas.Depths increased in the western and northernwest areas of the study area.It was also noted that farmers had left many wells, due to the drop in their water levels, and thus they had to drill another deeper well.The left wells and the water depth are shown in Fig. (3) and Table (1).The movement of groundwater flow was in two directions.The first direction was from the west towards the east, while the second one was from the west and northwest towards the southeast from Karbala to Najaf (Fig. 5).dh: the difference between the water stream level at two wells (meters).dl: the difference between the horizontal distance of the two wells (meters).Where the value of the hydraulic gradient to the north of the study area was (0.0005), the middle was (0.00041) and the south was (0.0012) (Fig. 6).7) were then analyzed by the correct methods of Neuman (1979) [7] and Cooper Jacob (1946) [8] for the unconfined aquifer [9].

Pumping-Test Experiments
1. Authority for Groundwater / Karbala (PW1) The total depth of the pumping well was (30) meters, the observing well was (82.26) meters away from it, and the depths of the water were measured in the pumping well (2.83) and the observing well (2.98) meters.The saturated thickness of the aquifer in that well was (27.1) meters, so the pumping rate was (8.0) L/sec (Table 2).The data from experiment (1) was analyzed in the aquifer test program by using Neuman's method for an unconfined aquifer (Fig. 8).It was found that the transmissivity by Newman's method is equal to 415 square meters per day, the hydraulic conductivity is 15.3 meters per day, and the specific yield is 0.026 (Table 6).The drawdown levels were recorded with time through the pumping well itself (single well test), with a total depth of (30) meter (Table 3).The depth of water was 8.9 meters and the discharge rate was 8 L/sec.Then, the data was analyzed using the program AQTESOLV by Neuman's and Jacob's correct methods for the unconfined aquifer.The two methods and curves are represented in Fig. ( 10) and the results of the analysis are shown in Table (6).The drawdown levels were monitored with time through the pumping well (single well test).The total depth of the well was 50 meters, and the water depth was 5 meters.When the pumping process began, the discharge was 8 L/sec, and the pumping continued for 105 minutes (Table 4).After that, the data was inserted in the AQTESOLV program and analyzed by using the methods of Neuman and Jacob for an unconfined aquifer (Fig. 10).The results are shown in Table (6).Fig. 10.Sheaee waqef well (PW3) by using Neuman's and Jacob's correct methods

4-Mohammed Hussain Farm (PW4)
The total depth of the well was 54 meters, the readings of the drawdown were recorded with time in the pumping well (single well test) with a discharge of 7 L/sec.The depth of the water before the start of the pumping process was 31.8 meters, and the pumping lasted for 105 minutes until the level stabilized (Table 5).Then, the data was inserted in the AQTESOLV program for analysis by using Neuman's and Jacob's correct methods for an unconfined aquifer.The curve of drawdown in the two methods is shown in

Fig. 6 .
Fig.6.Hydraulic gradient of the study area

Fig. 7 .
Fig.7.Locations of Test Pumping Wells in the study area

Fig. 8 .
Fig.8.The Authority of Groundwater / Karbala by Newman curve Method

Fig. 9 .
Fig.9.Ibrahim's Khalil well/Najaf (PW2) by using Neuman's and Jacob's correct methods3-Sheaee Waqef Well (PW3)The drawdown levels were monitored with time through the pumping well (single well test).The total depth of the well was 50 meters, and the water depth was 5 meters.When the pumping process began, the discharge was 8 L/sec, and the pumping continued for 105 minutes (Table4).After that, the data was inserted in the AQTESOLV program and analyzed by using the methods of Neuman and Jacob for an unconfined aquifer (Fig.10).The results are shown in Table(6).
Fig. (11); the results of hydraulic properties are shown in Table (6).

Table ( 1). Depths and head levels of groundwater in the study area
i: hydraulic gradient.

Table . 2
. Drawdown with time and depth of water for the Authority for Groundwater / Karbala (PW1)

Table . 3
. Drawdown with time and depth of water for Ibrahim's Khalil well/Najaf (PW2)

Table . 4
. Drawdown with time and depth of water for Sheaee Waqef well (PW3)

Table . 5
. Drawdown with time and depth of water for Mohammed Hussain Farm (PW4)