Hydrogeological Characteristics of the Aquifer in Shwan Sub-Basin, Kirkuk Iraq

This study includes determining the hydrogeological setting of the aquifer in the study area including groundwater measurement direction and the hydraulic characteristics of the aquifer. The study showed the existence of a shallow aquifer (unconfined) in the Quaternary deposits with presence of confined aquifer in the Bai-Hasan Formation. The construction of flow net showed that the groundwater flow is from the northeast to southwest (middle parts) of the study area and then to northwest towards the Lesser Zab River. The information of six wells three of them with observation well shows that the values of the transmissivity (T), hydraulic conductivity (K), Storage Coefficient (S) and specific capacity (SC) were ranged from (12.048 to 158.559 m 3 /day/m), (0.0848 to 4.545 m/d), (2.1 × 10 -4 4.67 × 10 -3 ) and (21. 6 to 166.956 m 3 /d/m) respectively, where (T) and (K) calculated by using (Aquifer Win program) software that depend on the methods of Cooper-Jacob and Theis recovery for analysis these information. The saturated thickness values for each wells collected from bank information of General Commission for Groundwater Kirkuk branch is ranged between (33 – 142) m. The aim of the research is to calculate the hydraulic characteristics and the flow direction, as well as the renewable and constant storage and the distance between the drilling wells in the study area.


Introduction:
Iraq is a country rich in water resources due to presence of the Tigris, Euphrates, Zab, Diyala, and Aludaim Rivers. Due to the low discharge of water in these rivers from neighboring countries, it is necessary to utilize the groundwater resources as an alternative resource. Water resources are decreasing continuously due to increasing demands water for different purposes, researchers conducted hydrogeological studies and surface water reservoirs and the ways to exploit them. Groundwater is found in the rocky gaps that carry water called aquifers [1].
The geological, morphological, and climatic factors which determine Hydrogeological conditions throug knowledge of spatial distribution of hydrogeological bodies and determine the groundwater recharge and discharge zones and the depth of the water table, while climatic conditions have determined the rate of groundwater recharge, the intensity of groundwater flow and water loss due capillary effects, evaporation and transpiration [2]. The previous studies which include study area are Parsons [3], which surveyed the groundwater resources inclusively based on the hydrogeological data gathered for the Alton Kopry basin. In addition, they suggested potential use of groundwater resource for agriculture and human purposes. Al-Naqash et al. [4], estimated and developed an operational program for wells drilled during the period of 2001-2003, by the General Company for Water Well Drilling in the Kirkuk governorate.
A hydrological study of the Alton Kopry basin was conducted by Abdul Razzaq et al. [5], concluded to the existence of two hydrogeological systems, the first is confined (Bai-Hassan formation) and the second is unconfined (Quaternary). Saud and Mohammad [6], Saud [7], studied hydrogeology and hydrochemistry of Kirkuk governorate in quaternary period, which included the study area. Thus study indicates the presence of groundwater in the Bai-Hassan formations and Quaternary deposits.
The aim of the study are determines the hydraulic characteristics of the aquifer in the These conglomerates had been the main reason for considering it as an independent formation, and has continental depositional environment resulting from erosion of the high mountains [8], [9]. Tectonically, it is located on the unstable shelf within the foothill zone as part of the Chamchamal-Butmah subzone. This zone includes asymmetrical long anticlines and synclines characterized by high dip in some places associated with joints and faults [10].

Methodology:
Pumping test conducted for six different wells at different locations on site in the study area as shown in Fig. 1. The groundwater level was measured by sounder in the pumping well. The electric conductivity (E.C.) was measured at the started of pumping and the end of pumping, a slight difference and this indicates that the well draws water from one aquifer.
The discharge was measured at the beginning of the pumping.
The water temperature were also recorded during pumping test. Observation well pumping test was carried out for (3) wells in the studied area with a constant discharge rate

Hydraulic characteristics of the aquifer in the study area:
Pumping and the recovery test process were performed on six wells diffusive in the study area as illustrated in Fig. 1.  Generally, the recovery test data are more reliable than pumping test data because the water level rises in the well at a constant rate without pumping effects. We note that the hydraulic characteristics of the wells in the study area are not identical due to differences in values of porosity and permeability of the water bearing layers.

Results and Calculations:
The experimental data and graphs for the six pumping tests wells in the study area and their locations are listed in Table 1 and Quaternary Deposits aquifer due to variations in lithology and porosity of aquifer. Table 2 Results of hydraulic characteristics by two methods used in single and observation well pumping test analysis for wells of the study area.

Hydraulic Gradient:
Groundwater moves from areas of high potential towards areas of low potential. The value of the hydraulic gradient of the study area is calculated according to the following equation [14]: Where: I: hydraulic gradient. dh: Head difference between two water points.
dl: Horizontal distance between the same two water points.
The value of the hydraulic gradient in the northeast , middle and southwest of the study area equal (0.031),(0.0056),(0.0049) respectively with an average of (0.0138) for all the study area.

Recharge and Storage of the Aquifer:
The bottom reservoir is the volume of water in the effective voids of the geological layer for the unconfined aquifer and the volume of water stored in the pores under the pressure of the artesian layers for the confined aquifer. In both cases, these reservoirs represent two quantities whose size varies from one reservoir to another. The first is a quantity with a dynamic function and time function the natural and border layer is known as renewable storage, and the second is the amount of static volume that is characteristic of the dimensions of the geological layer (its porosity and pressure) is known as constant storage [15]. The main water storage is the quaternary deposits. The geological map of the study area showed the extension of these sediments, and it was observed in the study area because it represents the main water reservoir in the basin, and the total discharge was calculated using the following equation [16]: can be planned. The nature of the investment and the conventional method of digging wells make it difficult to develop a fixed plan, but it is possible to develop general lines that define the method and the crew without specifying the location (randomly) as follows: (57.20 × 10 6 ) m 3 /year is to be carried out through drilling (680) wells, including the existing wells and the productivity of (8) liters/sec and the duration of operation equivalent to (8) hours per day and for the duration of (12) Month as follows: That is, the distance between a well and another must be approximately 120 m

Conclusion:
There are two more than one direction of the groundwater movement in study area, the groundwater flow is from the northeast to southwest (middle parts) of the study area and then These values indicate that the hydraulic properties of the aquifer vary from one location to another in the study area, attributed to lithology heterogeneity for this aquifer. The total discharge was calculated in study area is Q= 14.49 MCM/year, these represent the total discharge of the study area per year, which represents groundwater. Of the storage accounts of the aquifer in the study area, and the amount of renewable water from the annual rainfall in the area that infiltrated to the groundwater was 57.20 × 10 6 (m 3 / year) and the constant storage was 1044.5 × 10 6 m 3 and the amount of water consumed in the shallow wells in the region for general purposes and irrigation was 5.62 × 10 6 m 3 / year and thus an additional the number of wells that can be drilled in the future in the studied area and 615 wells the distance between a well and another must be approximately 120 m.