The assessment of hydrogeological characteristics and sustainable development of groundwater of Mahabad Plain Aquifer

Hydrogeological study of groundwater is important in order to accurately understand the characteristics of the aquifer and its behavior (Fitts, 2002; Todd & Mise, 2005). So that the prediction of the stored water volume and extractable water from an aquifer depends on the accurate estimation of hydrogeological parameters. The results of detailed hydrological studies of groundwater resources in a semi-arid country such as Iran can lead to the use of proper methods for exploitation of these resources and ultimately, to be consumed correctly and with the highest efficiency.
The main subjects of the quantitative monitoring of groundwater include the study of factors such as groundwater level, the discharge of selective utilization resources and the discharge of groundwater resources, which can be achieved by analyzing the changes in these factors over time and combining the results (Thangarajan, 2007).
In most cases, extraction of groundwater resources is excessive in terms of recharge amount and leads to a dangerous trend in aquifer conditions (Niamnsi & Mbue, 2009). The water balance is a quantitative issue of groundwater that is very important in development design issues and water resource management (Fetter, 1994; Gaur et al., 2011). Also, aquifer water balance studies can be used for optimal management of surface and groundwater resources (Peranginangin et al., 2004), application of its equations for pumping experiments in aquifers (Ruud et al., 2004), discharge forecasting calculations (Stephanie et al., 2010), and reducing damage caused by floods and droughts.
Previous studies on the groundwater resources of Mahabad plain was limited. Also, studies have not covered the entire plain area and is mainly related to the early parts of the plain. Therefore, the need for more and comprehensive studies in this plain is necessary.
In the study area of Mahabad plain various formations have different hydrodynamic characteristics due to the lithological variation that play an important role in recharging and discharging of groundwater aquifers.
Study of various geological formations is one of the basic requirements of hydrological studies in terms of Lithological effects on the quantity and quality of groundwater and the role of geological structures in relation to the formation of hydrodynamic units.
The recognition of different geological formations in terms of lithology effects, the quantity and quality of groundwater and the role of geological structures in relation to the formation of hydrodynamic units is one of the essential requirements of hydrogeological basic studies.
Considering that a large part of the aquifer recharging is carried out by the Mahabad river bed and the streams around the plain also due to the hydraulic relationship between different formations and alluvial deposits of the plain, the quantity and quality of groundwater resources of the Mahabad plain in relation to land formations Has been studied.
Methods and Material: The study area of the Mahabad Plain with an area of 829 km2 located in the Northwest of Iran, In the West Azerbaijan province and the Southern part of Urmia Lake (Figure 1).
Geology Geological formations have a major role in relation to the quantity of groundwater resources, depending on lithology, expansion and characteristics such as permeability.
The Formation of Pck, Pcbr and Pccs with its outcrops in the southern parts of the region, due to its very low permeability and limited expansion, has little importance on the quantity of water resources in the region. Pcmr Formation in the southern and southwestern part of the region, along with the topographic steep slope of rocky outcrop contains the formation water. The karstic structures of the Pr1 formation, along with seam, split and fracture systems, have increased the permeability of this rock unit and the formation of karstic springs in the north of the region. The low permeability of Shale and Tuff of the Cretaceous is indicative of the low importance of this unit for quantity and quality of the water resources of the region.
Qum Formation (Mq) forms the dominant lithology of the region, which has a very important role in recharging groundwater aquifer with high permeability due to the tectonic processes and gaps. Groundwater recharge of plain is enclosed exclusively in all areas of the Mahabad River (Qt) and the permeable horizons surrounding the plain boundary, including Quaternary sediments (Qt and Qsm) in some areas.
Structural features: The structural patterns in the region are the result of various tectonic events from the Precambrian to the Quaternary. Current structures of Mahabad plain have formed the last movements of the Alpine orogeny phase before Miocene.
Field studies in Mahabad plain led to the identification of two burial faults
Hydrology and Hydrogeology: Mahabad Plain is part of the Urmia Lake Basin. The altitudes of the plain margins, have little effect on the groundwater aquifer. However, Permian dolomitic rocks and Oligomiocene horizons are somewhat effective in recharging of the plain margine, due to the presence of joints and fractures and the possibility of the presence of karst phenomena. Recharging the aquifer take place throughout the year from the altitudes and through the Mahabad River bed with continuous flow.
Using the combination of exploratory drilling results and field studies, it has been determined that the main structure of Mahabad plain consists of the occurrence of alluvial deposits of rivers and Lake's fine-grained terraces.
The groundwater aquifer in this plain is unconfined with a thickness of 30 to 90 meters. The main direction of the flow is from the south to the north and in the direction of the flow of the Mahabad River.
Data Analyses: For the purpose of hydrogeological studies, determination of the aquifer characteristics and water balance, the data obtained from the Regional Water Authority of the West Azarbaijan Province has been of great help. The systematic observations of piezometric wells have been used to study the fluctuations and the depth of the water table.
In order to study the hydrogeological properties of the Mahabad plain aquifer, hydrodynamic coefficients of aquifer, as well as all the recharge and discharge factors necessary for calculating the groundwater balance were considered. To calculate the water balance of the plain, long-term average data were used at the dam site of the Mahabad River and the Gherd Yaghoub hydrometeorological station. Also, the water table, unit hydrograph of the piezomrter, and the unit hydrograph of the plain, drawn using the statistical period, and is used in calculations.
In order to calculate the Mahabad plain water balance in the corresponding calculations, the area between the dam reservoir (beginning part of the plain) and the Gherd Yagub Measuring station (end part of the plain) with the area of 829 Km2 has been used.

According to the exploratory well logs, it can be said that the whole plain except the plain border has upper layers have low permeability and lower layers at the top of the bedrock have high permeability. Alluvial deposits of the plain area can be divided into three zones due to the particle size and thickness, which is influenced by the flow regime governing sedimentation and tectonic processes.
Based on the isopotential contour of the water table for the dry and wet seasons, the main direction of the groundwater flow is from the south to the north and along the Mahabad River. Based on the isopotential contour of the water table depth in Mahabad plain, the maximum depth of the water table is 12 meters in the southeastern at the entrance to the plain and at least 1 meter of the north at the end part of the plain. In this area evaporation from groundwater over time causes massive salt marsh.
The quantity and quality of groundwater resources in the Mahabad plain will be more related to the quality and quantity of geological formations, surface water resources, soil texture, evaporation, and the effects of the advent of the saltwater frigate marshes. Based on the studies, it has been determined that most of the recharge of the Mahabad aquifer is in the input and middle parts of the plain, with the Mahabad River bed and the streams around the plain.
The significant difference in the transmisivity between the middle and the end parts of the plain is probably due to changes in the thickness of the layers between these two regions, which correlates with the related isopach map of alluvial deposits.
The aquifer specific storage coefficient is the reaction of the reservoir's water table against recharge and discharge. According to the calculations, the specific storage for the entire plain can be considered as 2%.
Measuring of water table and the result of the studding hydrograph of piezometers, indicate that the groundwater aquifer of Mahabad plain is completely saturated and changes in the reservoir volume during the water balance period are negligible.
Considering the hydrogeological characteristics of the aquifer of Mahabad plain such as aquifer thickness, flow direction, recharge and drainage areas and other hydraulic features, suitable areas for drilling extraction wells for utilization of groundwater are along the flow basin of the Mahabad River from the south to the north part of the plain.
The change in the volume of the reservoir was calculated according to the water budged equation and with regard to the parameter's unit was calculated to be .37 million cubic meters. Water balance in the plain can be calculated considering different climatic conditions and extraction of the network.
In this study, the state of the situation was chosen which has the most adaptation conditions of the existing situation and there is a high degree of certainty of continuous extraction without any particular changes.

According to hydrogeological studies, the most permeability and aquifer recharge of Mahabad plain is due to the Ruteh, Qom and Quaternary formations. Also, the results of exploratory drilling and field surveys in Mahabad plain led to the identification of two hidden faults, which caused sudden changes in the depth of the bedrock and the formation of depresion and abrupt changes in the flow path of the Mahabad River bed.
Identification of suitable areas for determining extracting areas, depth of wells, the rate of extracting from the well, the optimal use of groundwater with regarding to the minimum capacity of the aquifer extraction, are an appropriate guarantee for preventing any adverse effects, keeping the drainage volume down and producing the crop.
The optimal use of groundwater and taking into account the minimum volume to be removed from the table, the guarantee necessary to prevent any adverse events, keeping down the drainage volume forms and producing the appropriate product.
According to the results of the studies, considering the actual area of the aquifer of Mahabad plain (250km2) and the average depth of the water table in the water balance period (4m), the permissible annual allowable extraction water in the aquifer area is equivalent to 30 Millions of cubic meters per year. And to prevent mixing of brine and fresh water the value of groundwater table is 1279 meters.
The results indicate the aquifer balance state. In this way, optimal aquifer management and continuous development of groundwater are necessary in order to prevent adverse conditions in the aquifer area.
Considering the reduction of rainfall in recent years and in order to fulfilling the Water requirement of the area such as agriculture, optimal management of irrigation and reduction of groundwater use should be considered, in order to preserve the water resources of the plain.