3.2.1. Base maps
Aforementioned factors in previous part are criteria of finding the karstic locations and karstic water and essential material of the current study. In the first step, the controlling parameters in karstification are defined. These parameters and their effects on the karstification are evaluated in different areas and then each parameter is presented in a map based on its effect on the karst distribution. Data were mapped, classified, weighted and managed in separate layers in GIS software. Using GIS as the basic analysis tool for karst groundwater potential mapping can be effective for spatial and data management and manipulation, together with some reasonable models for the analysis. The required data and information more than 25 maps were gathered from the updated maps with proper scale and detailed references in geological survey and Mineral Exploration of Iran. This study includes 4 main steps to achieve an ideal site selection. These steps include; creation of a database, identifying the factors influencing the karstification, scoring the factors and validation of results. The details of each step are presented in Fig. 2. This article is based on geological and hydrogeological properties as study were carried out in the Geological Survey of Iran. The effect of each of these parameters on the karstification is shown in Table 1. The values presented in this table are often obtained experimentally
Figure 2.
Table 1.
Iran faults and folding map
The outer rigid surface of the Earth is divided into chunks known as tectonic plates. These plates move around at the rate of a few centimeters per year. The Iranian Plate is a small tectonic plate thought to underlie Iran and Afghanistan, and parts of Iraq and Pakistan. It is compressed between the Arabian Plate to the southwest, the Eurasian Plate to the north, and the Indian Plate to the southeast. This compression is likely a cause for the very mountainous terrain of the area including the Zagros Mountains. Tectonic features of Iran include faults (3 types) and folding map (anticlines and synclines) are mapped from geological survey and Mineral Exploration of Iran (Fig. 2).
Climate parameters maps
Iran is a country with an arid-to-semiarid climate (an average precipitation of 240 mm/year), with the exception of the northern parts which receive up to 2,000 mm precipitation per year. High precipitation such increases the karstification potential but dryness negatively affects the karstification. Precipitation map is used in this article (Fig. 2). Precipitation is classified to four classes (Table 1) between less than 100 and more than 500 millimeter per annual (mm/a).
Climate map of Iran is prepared based on some parameters such as temperature, precipitation and evaporation. Temperature is classified to three classes (Table 1) between less than 20 and more than 25 degrees Celsius. Also, evaporation is classified to three classes (Table 1) between less than 2500 and more than 3500 millimeter per annual. Final, Climate map of Iran based on mentioned parameters is classified to three classes include humid, semi-humid, and dry climates.
Geomorphological features maps
Morphology means presence of a network of holes by karst processes. So, morphology of a karstic region and subsequently its hydraulic features and conditions change in long term. Karst morphology is usually described in carbonate rocks like limestone, dolomite and marble. Surface and subsurface karst morphologies are the key components for understanding the nature and genesis of cave and karst systems (De Waele et al. 2009). The experiences show that anticipating the surficial karstic features to be an absolute representative of the karstic features in the depth might result to many mistakes in hydrogeological studies (Ford and Williams 2007).
The karst resources in mountainous areas are focused on distribution and protection in various forms despite the low level of anthropogenic disturbance. The karst water resources in the plain areas have development potential and may be used to meet the needs of large-scale agricultural irrigation and urban water use, although it is necessary to quantitatively specify the limits on water exploitation in order to prevent natural disasters (Jiang et al. 2021). According to Seif and Ebrahimi (2014) densities of caves and springs show a good correlation with the evaluated karstification. The investigation of caves in Iran (about 850 caves) shows the predominant role of hypogene processes in the formation of many of them (Karimi Vardanjani et al. 2017). The caves maps of Iran are used in this stage. Distance to Caves are the main factor in this stage, less than 1000 to more than 3000 meters (Table 1). Limestone is susceptible to both physical and chemical weathering. So, present and paleo climate need to be considered in the karstification potential studies. The paleo climate can affect weathering over time, so paleo weathering mapping was on the agenda (Fig. 2) include chemical and physical weathering (Table 1).
Lithological maps
The lithological studies in this article are classified to mineralogy, age, layering and thickness. The primary type of porosity is the interparticle porosity but it is affected by different types of diagenetic features such as cementation dissolution and fracturing in carbonates. Different types of barriers such as impermeable and cemented layers might stop the fluids in different directions in the subsurface. Dissolution is very important in hydrogeology and engineering geology because different volumes of fluid might entrap in dissolution enlarged pores. This is very important in drilling a well or making an underground structure such as a tunnel. The dissolution potential is classified to three factors including the mineral and chemical composition, purity of the mineral, compaction and cementation. The purity of carbonate rocks, mineralogy, based on the data bank of the geological survey of Iran are classified to four classes include pure and impure limestone and dolomite rocks (Fig. 2 and Table 1). The thickness of soluble rock layers and the stratigraphic position of them among the non-soluble layers control the extent of karst development. In the case of thin soluble rocks sandwiched between non-soluble layers, it is less likely that karstification occurs (Seif and Ebrahimi 2014). So, the thickness of carbonate rocks is classified in this article (Table 1). The layering of the carbonate formations is used in the map (Fig. 1). This parameter is mapped based on four classes (Fig. 2). Other parameter related to lithology is permeability of carbonate rocks which shows at Fig. 2. This parameter is classified to three categories include high permeable, low permeable and non-permeable rocks (Table 1).
Most of the outcropping carbonate rocks are of Cretaceous and Tertiary age. From the hydrogeological point of view, the most important karst aquifers in the Zagros region are Sarvak (Cretaceous) and Asmari (Palogene - Neogene) Formations, in the Alborz region is Lar Formation (Jurassic), in the Kopet dagh region are Mozduran and Tirgan Formations (Cretaceous), and finally in the Central Iran are Jamal (Permian), Shotori (Triassic), Esfandiar (Jurassic), and Qom (Neogene) formations. In this article, carbonate rocks at three Era (Paleozoic, Mesozoic, and Cenozoic) in Iran are considered.
Water resources maps
Springs are important sign in the hydrogeological and karst studies. The discharge and distribution of the springs are controlling factors in this category (Table 1). One of the most important characteristics of every spring is its rate of discharge. Considering an average discharge (Qs), the karstic springs in Iran may be classified as two classes include lower and higher than 25 liter per second (Fig. 2). Quality of the water is very important which needs to be determined in the next step. Karami et al. (2016) characterized by a high rate of precipitation and recharge via highly permeable fractured karstic formations. To investigate groundwater spring flow, the physicochemical parameters include major cations and anions, discharge, EC, pH, and temperature were studied by Karimi et al., 2018. The drainage pattern is distinguished from other types of lineaments to highlight its role on karstification (Hassanpour and Mohammadnejad 2015; Shokri et al. 2014).
3.2.2. Parameter classification maps
Classification of the study area based on affecting components on karst water potential include tectonic, hydrogeology, lithology climate and geomorphology is next step of methodology. Karstification potential maps based on factors include tectonic, hydrogeology, lithology, climate, and geomorphology are shown in Fig. 3.
Figure 3.
Tectonic condition
In hard rock areas, fractured zones are important to be identified and characterized since they lead to preferential groundwater flow pathways and enhance well productivity. Faults can guide water to penetrate into the ground; therefore, karstic processes can developed along them and result in a variety of karst morphologies (Jafarbeyglou et al. 2012). The zones with the highest lineament density are often those with the most intense karst development (Goldscheider and Drew 2007). Active tectonics causes periodic changes in karst base level, folding structure and faults, and due to these processes, some parts of old conduits are truncated and deactivated (Chitsazan et al. 2015). Large faults are rarely represented by a single surface fracture. Minor faults usually feather off at acute angles as a consequence of the wrenching of the rock. Shear fractures are often oriented parallel to or close to the associated structures (Ford and Williams 2007). The faulting zones and fractures affect different aspects of the hydrogeological systems (Hauselmann, et al. 1999, Faulkner et al. 2010; Fairley et al. 2003; Wibberley and Shimamoto 2003; Sharifzadeh and Kargar 2007; Altafi Dadgar et al. 2017). One of the most useful methods in karst water resource evaluation is comprehensive analysis of karst related features (lineament, fault, joint) from aerial photo, satellite image, geological map, fieldwork data and also hydrological data processing. The majorities of karst poljes are predisposed by tectonics and thus are formed and shaped by the influences of exogenous factors and processes (Milanovic 2004; Nassery and Alijani 2009). Faults control domain vessels of the water movements (Anderson and Fairley 2008). Vertical faults show higher capability of water conduction to the depth (Zarei et al. 2010). Generally, the karstification pattern obey the faults and fractures direction. The normal faults in extensional system are more effective for the hydraulic movements in comparison to the reverse faults in tensional system. The effect of different features such as fault breccia (which makes the water movements easier), joints (where the pressure on the joints decreases by erosion) or thrust faults (affecting extensive area) are important in hydrogeology. The effect of fractures on hydrogeological properties depends on: 1) the spatial direction and density (number of the fractures in a specific length), 2) the connection between the fractures, 3) the width of the fractures, 4) roughness and the hydraulic conductivity of the fracture filling materials. Based on the Fig. 1a, normal faults are distributed vastly. These areas are considered for the highest potential of the karstic features in comparison to the other two types of faults in the first levels of karstic potential study. The major and minor faults and their effects are studied in addition to the kinematic classification of the faults and their effect on karstification. Opportunities for karst development are most likely in the center of the fault zone. The distribution of this parameter is shown in Fig. 3.
Hydrogeology
Karstification potential maps based on hydrogeological factors include discharge rate, distribution, and quality of springs, as well, as permeability coefficient is shown in Fig. 3. Karst aquifers are those in which caves or conduits form an important part of the flow path. Conduit permeability ranges from pipe-like openings greater than one centimeter in aperture to caves many meters in aperture. Discharge from karst aquifers is through large springs. Spring discharge tends to respond rapidly to storm flow. So, the discharge rate and location of springs are the main components in hydrogeological karst potential. Permeability is the capacity of an aquifer for transmitting water and it represents the relative ease with which the aquifer transmits groundwater. Permeability of karst areas is another effective component in hydrological karst potential. Finally, water quality can be considered for prepare the hydrogeological component of karstification potential map.
Lithology
Lithology is a key component in the development of karst, and the difference in erosional resistance between lithology will influence the landscape as a whole. Limestone is susceptible to both physical and chemical weathering. It must be noted that the harder is the lime stone, the more is the probability of karst landforms formation; because soft rocks are crumbled quickly and different landforms are not created in them (Hajati Ziabari et al. 2014). Generally, limestone shows higher potential for dissolution in comparison to dolomite. Dolomite is the diagenetic type of carbonate rocks thus shows higher resistivity to dissolution and different types of environmental alterations. The lithology of the carbonate rocks is important in the porosity, permeability, and consequently the karstification potential. Karstification potential maps based on lithological factors include mineralogy, age, layering and thickness is shown in Fig. 3 each of which is described in detail in the previous section
Climate
Iran is a vast country, and has different types of climate: mild and quite wet on the coast of the Caspian Sea, continental and arid in the plateau, cold in high mountains, desert and hot on the southern coast and in the southeast. Karstification potential maps based on climatical factors include precipitation, temperature, evaporation, and finaly climate categories is shown in Fig. 3. The impact of changes in the height could be checked at climate factor, value and type of precipitation as well as value of temperature. For this reason, the height factor based on Digital Elevation Model (DEM) is considered, less than 1000 and more than 3000 meters above sea level (m.a.s.l).
Geomorphology
Karstification potential maps based on geomorphological factors include cave, weathering, paleo-weathering, and paleo-geomorphology is shown in Fig. 3. Karst landscapes and Karst aquifers are formed by the dissolution of carbonate rocks by water rich in carbon dioxide waters. There are more than 850 caves in Iran which the length of most of them is less than 1000 meter. The short term length of these caves has been attributed to the active and developing nature of the orogenic belts in the country and the continuous shifts in the erosional base level. Although karst landscapes are often dominated by underground drainage networks that interrupt and capture surface water flow, the landforms result mostly from chemical weathering of the host rock and the progressive integration of subsurface cavities. So, paleo-weathering and paleo-morphology are main factors in karst water potential. Therefore, the role of geological age of karstic outcrops is an important point that should be considered.
3.2.3. Weighting and analysis
One of the most important steps in the site selection process is assigning a value or weight to each factor or information layer (Hassanpour et al. 2017). Veress (2020) presented hierarchical classification of the Earth’s postgenetic karsts and described karst types (Veress 2020). The Analytic Hierarchy Process (AHP) is used for weighting of selected criteria in this study. Generally, the AHP method converts a multi-dimensional to a one-dimension issue and simplifies a complicated problem for making a rational decision. This is a subjective process which can result in differences in opinions between specialists in each of the main parameters. Thus, the approximate weight of the parameters was averaged. Finally these parameters evaluated based on the different views among the experienced expert. The result of AHP weighting the considered criteria of karstification is presented in Table 2. All the controlling factors in the third layer, second layer and the first layer are presented in the table. The weights of the criteria and defining the weight vector is determined by the following two equations, first by normalizing the pairwise matrix (Eq. 1) and second by determining the average of each row (Eq. 2).
$${r}_{ij}={a}_{ij}/{\sum }_{}^{m}i=1 {a}_{ij}$$
1
$${W}_{i}={\sum }_{}^{n}i=1 {r}_{i/n}$$
2
The final grade is determined by assimilating the data layers’ coefficients (Eq. 3).
$${V}_{H}=\sum _{}^{n}k=1 {W}_{k}\left({g}_{ij}\right)$$
3
Table 2.