Groundwater Simulation and Wells Distribution at Qazaniyah City in Diyala Governorate

In recent years, there is more interest in water sources availability, including groundwater due to an increase in demand for water because of the increasing population in the world, and the water recedes due to climate change also. Therefore, the study of groundwater has required more attention. The aim of the present study is to establish a MODFLOW model in the groundwater modeling system software to simulate the movement of groundwater in the Turssaq alluvial fan which is located in the Qazaniyah city, east of Diyala Governorate. The solid model was used to define the aquifer in the study area. Using the GIS software, mapping and preparing the data needed to create a conceptual model were carried out. The data of the wells were used to create and define the aquifer, then a three-dimensional model was created. Measuring the water table for some wells were simultaneously monitored to determine the hydraulic conductivity values of the aquifer through the (PEST) package provided by the software. The hydraulic conductivity value of the main layer was 18 m/d. Then several readings of observation wells were recorded for the period extended from 1/Nov/2018 to 22/May/2019 for the calibration process in the unsteady situation and to determine the coefficient of storage. The value of the storage coefficient was defined as 0.001. Several scenarios were conducted for the study area to find the best distance between the wells. Three distances were tested, 500, 1000 and 1500 m. The operating periods were 6, 12 and 18 (hours/day). Results obtained from the model show that the best distance between the wells is 1000 meters with a maximum operating rate of 12 hours/day. The maximum discharge with the lowest distance and the lowest drawdown of the groundwater table are considered.


INTRODUCTION
Groundwater is considered to be the second most important source of raw water, and it has been cared for since ancient times. It is available in most places, even in desert and dry places (Karanth, K. R., 1987). It was easy to extract and have low cost compared with other sources. It was often pure from impurities and plankton and did not need to be filtered because the aquifer act as a filter to clear the water, and it does not contain microscopic organisms or bacteria (Abdulla H. H., 2001). Climate change in the region, lack of rainfall, and increased demand for water in most parts of the world and Iraq (Toure, A., Diekkrüger, B., and Mariko, A., 2016), as imports of rivers and valleys have declined due to human activates and climatic change. Therefore, the people resorted to use groundwater as an alternative source of surface water. Rainfall is the main source of groundwater recharge, and the amount of groundwater is not infinite, which must set the conditions and controls to be used optimally and maintain its sustainability (Chitsazan, M., and Movahedian, A., 2015). The excessive use of groundwater leads to a decline in their levels and thus lead to the drying of wells and springs. Therefore, in this study, the modeling of groundwater in the Qazaniyah City was highlighted, where wells and springs are currently used. The Turssaq alluvial fan is identified as a study area due to its importance and the abundance of wells and springs therein. The Qazaniyah City is located between latitude 30˚45'00" N and longitude 45˚30'00" E, at the east of Diyala Governorate, near the Iranian border, as shown in Fig. 1. The city suffered from a lack of surface water sources. The population and agriculture in this city have been influenced by surface water deficit, and people started using groundwater as an alternative source. Many wells have been drilled randomly in these areas, also the use of groundwater is not ideal, so it is necessary Journal of Engineering Volume 26 September 2020 Number 9 97 to study the characteristics of groundwater in this city and create a conceptual model by using (GMS) Groundwater Modeling System software.

Figure1.
Location of the study area (GIS Map Online).

RESEARCH OBJECTIVES
The present research aims at developing a MODFLOW model to simulate the groundwater movement in the Turssaq alluvial fan and specifying the hydraulic characteristics of the aquifer for the study area by using Geographic Information Systems (GIS) and Groundwater Modeling 98 System (GMS) software, as well as determining the best distribution of wells with best operation conditions.

EQUATIONS GOVERNING GROUNDWATER FLOW
The governing equation used to estimate the three-dimensional groundwater flow in the GMS software and the determination of water levels is the Darcy equation and in accordance with the law of conservation of mass. where: x, y, z = Cartesian coordinates, m, Kx, Ky, Kz = The hydraulic conductivity, m/day, h = Head of groundwater pressure, m, W = Flux per unit volume, m 3 /day, t = Time, day, and, Sy = Specific yield for the porous medium, dimensionless.
Two methods can be used to create a developed MODFLOW simulation in the groundwater modeling system-first, the grid method, or the conceptual model method. The grid method includes working immediately with the 3D grid and applying sinks/sources and other model parameters on a cell-by-cell basis, (GMS User Manual 10.4, 2018). However, the conceptual model method includes using the GIS tools in the Map module (Dawood, A. S., 2018) to improve a conceptual modeled study area. The location of sinks/sources, layer parameters (like hydraulic conductivity), and all other data required for the simulation can be defined at the conceptual model level. Once this model is complete, the grid is generated, the conceptual model is converted to the grid model, and all of the cell-by-cell assignments are performed automatically (Wang, S., et al., 2008). The conceptual model is the best way to create complex models for easy handling with lots of data. The steps of creating a three-dimensional conceptual model in the GMS software include three main steps; firstly, is the establishment of the solid data model, which represents the aquifer and type of material. Secondly, creating boundary condition layers, that includes the recharge layer, sink and source water layer, border layer, and observation wells layer. Finally, the 3D grid and the MODFLOW layer is created. Fig. 2 illustrates the methodology of developing the three-dimensional conceptual model for the study area with the necessary data step-by-step, as well as the calibration process of the model. Figure2. The methodology of developing the conceptual model groundwater simulation.

Specifications of the study area
From the previous figure, the first stage of the model development is achieved by collecting the wells' data, hydrological, geological, and climate data for the study area.
1. Geological data; The geological formations found in the study area are Lower Bakhtiari (Al-Muqdadiyha). It consists of sandstone, silt, and Claystone. This type of formation is for the confined aquifer that extends into the lower layers of the study area (Jiburi, Hatem K., and Naseer H. Al-Basrawi 2015). Above this layer, the alluvial fan was formed and is considered one of the modern formations resulting from the flow of water in the flood seasons of Wadi Turssaq. The fan was composed of several layers formed from coarse materials such as gravel and sand deposits in high discharges of the flood in the lower layers, and then the fine sediments above that layer to form a higher layer with low permeability during the low discharge, Fig.3 2. Hydrological data; the study area is located on the foot of the mountains in eastern Diyala province near the Iraqi-Iranian border. It contains many valleys having a seasonal flow during the rainy period (Ali M., 2007). The Wadi Turssaq is one of its most important valleys. Fig. 4 shows the hydrology map of the study area. The map was drawn by using Hydrological tools in GIS Software. The stream order in the legend of the map represented type of valley. 3. Climate data should be taken into consideration at the calculation of the quantity and quality of groundwater. Rain is the primary source of groundwater as a direct recharge, where there is an indirect recharge of groundwater from other sources. Direct feeding is estimated at about 5% from rainfall (Ali, S. M., and Oleiwi, A. S., 2015), and indirect feeding results from the deep percolation of water flow in the valleys and from surface irrigation of agricultural crops. Table  2 shows the amount of rainfall in the Mandali region for the period 2010 to 2019. Rainfall data depended on the Mandali station data because it is the closest station to the study area.  The boundary of the Turssaq alluvial fan, the boundary of study areas, can be drawn from satellite images, geological maps, and wells sites. This border will be included in the simulation model. Fig.5 shows the boundary of the Turssaq alluvial fan in Qazaniyah city. Since there are no natural boundaries, so the boundary will be defined as a constant head in the conceptual model (

Modeling of Groundwater Flow
To create an integrated MODFLOW model it is necessary to create several basic models, where each model carries specific characteristics, and then consolidate the obtained data in the main model

Solid model
This model represents the geological formation. It was created from the cross-sections of the wells and the geological map of the study area. Fig. 6 illustrates the geological formation of the alluvial fan, which consists of four layers. From the geological properties of the layers can be estimated the hydraulic specifications of each layer. Table 3 represents the estimated values that will be adopted and validated at the steps of the calibration of the model.

Conceptual Model
This model represents four secondary layers. First, the boundary layer includes the type of boundary in the model and the starting head, as shown in Fig. 7. Second, the sink source layer, which includes wells data. Third, the recharge layer, this layer represents the amount of water that feeds the groundwater from the rain. The estimated percentage was 5% (Ali M., 2007) of the annual rainfall rate as an initial guess rate, which will be verified during the calibration of the model. Finally, it represents the wells' observation layer.

Grid and MODFLOW models
The three-dimensional grid model of the Turssaq area was created. The origin of the grid model is 3703000N, 558500E (UTM), and 20 meters under sea level. The lengths in the direction of X, Y and Z were 22450, 16950and 220 meters, respectively, cell lengths in the direction X and Y are 100 meters, and the number of layers in Z direction was five layers, the high of the cell depends on the top and bottom elevation of the aquifer. The total number of cells was 191250, the number of Journal of Engineering Volume 26 September 2020 Number 9 106 active cells was 119740, and inactive cells were 71510. The dimension of one cell is 100x100 m, and the area of the cell will be equal to 0.01 km 2, as shown in Fig. 8.   Figure 8. The grid design of Turssaq Alluvial Fan

Determination of Hydraulic Properties of the Aquifer
In this step, the software is run in a steady-state, and after several cycles, the software will correct the initial values of hydraulic conductivity and groundwater recharge rate (Ahmed, A. A., 2009). Table 4 represents the final results for these values. At the same time, the calibration of the model was accomplished by matching the simulated water tables at the observation wells with the field measuring water tables of the observation wells, Fig. 9.  Figure 9. Comparison between observation and computed heads at the steady-state condition.
The specific yield and storage coefficient can be calculated in the same way as the hydraulic conductivity was calculated. The first step in an unsteady state is to convert the MODFLOW model from a steady to unsteady form, then import the transient data like transient water table data of observation wells in the study area. Table 5 presents the observed heads of two wells for the period (11/1/2018 till 5/1/2019), and Tables 6 and 7 illustrate rainfall data and pumping data, respectively.

5-Field observations
Several field observations were conducted to be used in the calibration and verification of the numerical model. The wells W24 and W18 were selected as observation wells in the study area, and then water tables were recorded during the research period. The selection of these wells was because they are located in the center of the study area. The readings were taken at stable times, and there was no pumping from these wells as shown Fig. 10.
MODFLOW model is constructed where all of the hydraulic soil properties are specified, as shown in Table 8. The simulated head is compared with the recorded head in two observation wells W18 and W24, as shown in Fig. 11 and Fig. 12

Results of Suggested Scenarios
Several scenarios were implemented to simulate and assessment of groundwater of the Turssaq alluvial fan to simulate the groundwater flow and testing all operation conditions of drilled wells, then defining the best distribution of drilled wells and the appropriate number of wells in the specific study area. To determine the best distribution of wells with the best operational conditions it is necessary to redistribute the wells and change the operating times then compares the results and determine the best scenario (Jalut, Q. H., Abbas, N. L., and Mohammad, A. T., 2018). The scenarios that will be applied in the study area are the redistribution of the wells so that the separation distances between the wells are 500, 1000, and 1500m. The pumping times are 6, 12, and 18 hr/day, and the adopted productivity of the well is about 7 l/s for all cases. The recharge rate will be 0.000108 m/day, as calculated in the model. The results for the assumed scenarios and the comparison of the results are presented in Table 9. From the results illustrated in Table 9, it can be noted that the drawdown of groundwater in the first scenario is very high, causing dryness of the cells in the model. So, the distance of 500m between the wells is unacceptable at any time conditions. When the distances between the wells are 1000 m, the average value of the drawdown water table is acceptable during the low and medium operating periods. In contrast, the drawdown of the water table increases during the operation period of 18 hours. When the separation distances between the wells are 1500m were used, the drawdown in the water table is acceptable with all operating conditions. So with the third scenario, the drawdown was low compared with other cases. Still, the total discharge at the maximum operation condition was less than the amount of wells discharge in the second scenario.
The daily operating rate of the pumps will be variable as the running hours in winter are less than in the summer. Besides, operating hours in the urban area are less than in agricultural areas. The nature of the study area is agricultural land, and it is famous for the cultivation of wheat and barley, which are winter crops. Therefore, the average operating hours per year does not exceed 12 hours/day. However, a distance of 1000 m between the wells will be the best distance that can be adopted.

CONCLUSIONS
The main concluded of establishing a conceptual model for the Turssaq alluvial fan are to simulate groundwater movement and calculated the hydraulic properties of the aquifer with the best distribution method for wells and the best operating time as follows: 1-It was found that the study areas consist of four layers. First, the upper layer of the surface of the earth, which was a mixture of sediments of the modern era. The second layer was an impermeable layer that is formed of clay mixed with sand and gravel with a thickness of 15 m. The third layer consists of a mixture of sand and gravel, which is the main storage layer and is a confined aquifer. It has a thickness of 20 m, and the hydraulic conductivity is 18 m/d, and the transmissivity is 360 m 2 /d. The last layer is impermeable, which is the formation of Al-Muqdadiyha.
2-The developed conceptual model for the study areas was well simulating the groundwater flow and gave accurate results compared with the field observations, at the same time, the calibration of the model was accomplished by matching the simulated water tables at the observation wells with the field measuring water tables of the observation wells 3-Several scenarios were tested to predict the best distribution of wells in the study area, as well as to define the best timing of the operation. It was found that the best distance between wells is 1500 m has an acceptable drawdown. But for providing adequate water to cover the high percentage of demand, the operation time of 12 hours a day with a separation distance of 1000 m was adopted. That was due to the unharmed water table caused and expectable drawdown results. 4-The distance between wells 500 m or less and the extensive operation of these wells, that actually use, is unacceptable under any operational time condition. And the operation of these wells simultaneously together will lead to a significant reduction in the groundwater table and inability to recover of the water table with an existent recharge.