جستجوی مقالات مرتبط با کلیدواژه « karst » در نشریات گروه « آب و خاک »

For groundwater development, necessities are needed to detect different aquifer layers hydraulic parameters in an area , which can be used to explicitly define the type of aquifer and the thickness of its aquifer layer. Geoelectrical method is one of the most effective tools in determining and separating subsurface layers. The electromagnetic method as well as ,is a newer method that can play an important role in determining the potential of subsurface layers with acceptable accuracy. In this research, 10 electromagnetic logs were used to investigate the thickness and separation of the aquifer layer of 5 karstic springs in Famaseb, Faresban, Gian, Ghale Baroodab and Gonbad kabood in the Nahavand plain of Hamedan province. Logs were measured in the upstream of each spring, then the results of electromagnetic extraction were checked in different frequency ranges. Finally, the output of electromagnetic logs were compared with 5 logs of the Geoelectric method, which showed that the similarity in results of the two methods . The final results showed that there is an aquifer layer in Famaseb spring up to a depth of 6 meters, Faresban spring to a depth of about 20 meters, Ghale Baroodab about 10 meters appearing with joints and fractures in these springs, Gian to a depth of about 2 meters . The Gonbad kabood has an aquifer layer of up to 36 meters. The highest thickness of the aquifer layer was estimated in Gonbad kabood spring and the lowest in Gian spring.

Determining the capture zone of water resources is a strategic approach proposed at the national level of water resources management in Iran. One of the important actions for this purpose is protection of karst water resources, which are considered one of the vital sources for supplying water due to the widespread karst formations in this country and the limitation of groundwater resources in alluvial aquifers. Generally, water flows out through the springs in the karst system. The land area where the water contributes to the spring is called the spring's capture zone. The study and analysis of the recession curve of the springs, the area extending from a discharge peak to the base of the next rise, along with the other physical characteristics of springs such as electrical conductivity is a useful indicator for getting knowledge about the condition of the catchment area and other properties of the heterogeneous karst terrain. In estimating the water budget, unlike the non-karst areas where the surface runoff or the outflow is considered the main factor in the estimated water budget, the recharge component is an important factor in the karst domain. The difference between hydrogeological and hydrological (topographic) catchments is one of the obvious features in karst landscapes. The identification of these basins or their boundaries is possible by combining geology and topography information. Soufiyan Cement Company in the vicinity of Chelleh Khanehe Olya spring located in Moro Mountain is associated with the creating social problems due to the expansion of mining activities and the negative impact on spring water in this area. Therefore, this study aims to determine the catchment area and the capture zone of the Chelleh Khanehe Olya spring by determining the protective boundary for the extraction of limes by the Soufiyan cement factory to prevent the negative impact of this factory on the spring.

In this research, the hydrograph of the recession curve related to a rainfall event has been analyzed by taking into account the mean monthly discharge rate of spring to determine the sub-regimes of diffuse and conduit flow by employing the following equation:Qt=Q0e-αt (1)Where Qt is the discharge rate at time t, Qo reveals the discharge at the initial time, and α is a recession coefficient.In addition, The Qmax/Qmin ratio has been calculated to estimate the flow type and the degree of karstification in the catchment area.In the next step, to determine the Chelleh Khanehe Olya spring catchment area and its capture zone, spring hydrogeological boundaries were determined and investigated using the SCS method and estimating the area's water budget. Due to the lack of sufficient rainfall and groundwater discharge information in this region, the water budget for a given period (2019-2020) has been computed indirectly by measuring the monthly discharge rate from the selected stations. After collecting the required data, the following equation developed by Milanovich (1989) has been used to estimate the water budget as follows:P=E+R+I   (2)Where P, E, R, and I denote precipitation (P), evaporation at the basin level (E), runoff (R), and recharge to the aquifers (I). All the parameters are in mm units.

Analyzing the variation of electrical conductivity along with the discharge rate indicates that by decreasing the discharge rate from 2.5 l/s to 8.1 l/s, the electrical conductivity increase from 463 µs/cm to 500 µs/cm, reflecting an increase in the volume of the reservoir, the dilution of the aquifer. The hydrograph recession curve during 2019-2020 indicated two laminar and turbulent sub-regimes. Micro regimes α1 (01.002) and α2 (0.013) represented that the dominant system of karst development in the region is diffuse. The high density of fractures and the lack of purity of lime are the main reasons for the weak development of the karst fracture in the region, which the Chelekhaneh Alia spring recession curve analysis,  maximum to minimum ratio of discharge, and karstification coefficient confirmed this issue. Determining the catchment basin using geological, hydrogeological information, and water budget showed that the hydrological and hydrogeological boundary of the spring is different. The protected zone of Chelekhane Alia spring, which includes the total hydrogeological basin and the Cretaceous limestone area below the level of the spring, was estimated to be about 184,000 square meters (18 hectares). According to the findings of this research, Sufian Cement Factory does not have the right to enter the hydrogeological boundary to extract limes, and on the other hand, to prevent the water level from decreasing due to the excessive extraction of lime as a result of the excavation depth reaching the level of the water table, it suggests to extract from the unsaturated part of the aquifer (unsaturated limes) to prevent the flow rate of Chele Khana spring from decreasing and even drying it up.

Analyzing the discharge rate, electrical conductivity, hydrograph recession curve, and its recession coefficient(α=0.002), revealed that the dominant flow in the system is diffuse, which results from the high density of fractures and region lithology consisting of impure cretaceous limestone. Since the result revealed the inconsistency between hydrological and hydrogeological boundaries, the geological profile of the site was prepared and the spring of the catchment was estimated. Based on the findings of this research, the Chelle Khanehe Olya capture zone consists of the hydrogeological area, obtained from the groundwater budget estimation, and the protective boundary for the limestone below Cheleh Khaneh Olya spring (the unsaturated zone of the area's limestones), which covers an area of about 18 hectares.

In recent decades, changes in climate and social norms in the direction of uncontrolled extraction of groundwater resources have led to a sharp decline in groundwater levels and a reduction in the karst springs discharge. Springs that have a smaller catchment area, where a part of their catchment area is located in alluvium, and there is more connection between karst and alluvial aquifers, are more vulnerable to human activity. To evaluate these effects, karst springs in the central areas of Kermanshah province have been studied. Accordingly, four dried-up springs in the region have been studied more accurately, indicating a significant relationship between the groundwater level in the surrounding alluvium and the karst spring discharge. The study aimed to estimate the minimum groundwater level to maintain the karst springs discharge. According to the findings, if the groundwater level around the springs reaches or less specified amount, these springs will be dried. This level has been named the minimum allowable groundwater level (MAGWL). The way to preserve the springs is to keep the groundwater level of the surrounding areas above the MAGWL. According to the average annual decrease of groundwater level in the study area, the need for management and control of the extraction from the alluvial aquifers is strongly felt.

Unsustainable development without considering regional planning can create adverse environmental effects, especially in karst water resources of a region from a qualitative point of view. Accordingly, in this study, a combination of two methods for determining spring vulnerability and qualitative zoning by MDHT method was used. This study was performed for three springs downstream of Seymareh Dam for a period of 5 years. The results showed that the value of vulnerability index in S1 spring was higher than the other two springs and the value was 150.4. Analysis of the results showed that the degree of vulnerability was an inverse function of spring discharge. By increasing the amount of discharge, the vulnerability index decreases. Considering the choice of MDHT method for qualitative zoning of the spring and the role of flow rate in determining the zoning scenario, the highest flow rate was related to S3 spring. The value of obtained MDHT index was also higher than the other two sources and the value of 417 has been calculated. The lowest flow rate was related to S1 spring and the MDHT index value was 14.75. The highest level is related to spring S1 and the lowest level is related to springs S2 and S3. The results show that the karst network of springs in the region is vulnerable, which affects the quality of these resources and sensitive areas of the region to develop exploitation are strongly associated with the risk of pollution.

Construction of dams on limestone formations, however morphologically, has an appropriate form; but usually causes seepage from the reservoir to the downstream. Also, the construction of a dam on calcareous-karst formations has the risk of over seepage from the reservoir, and the existence of the karst leads to complicating this issue. Therefore, various methods of hydrogeological analysis are needed to determine the condition of karstification of reservoir and dam axis in the karstic areas. Beheshtabad dam is in investigation studies stage and approximately situated at the far end of the anticline axis named Sangwill, which composed of dolomitic limestone with roughly 700 meters thickness. The right side of the reservoir is mainly in direct contact with this karstic formation. Hydrogeological analysis for determining the reservoir’s seepage in right side are including measurement of water level and boreholes hydrochemical analysis, measuring springs discharge and hydrochemical condition of springs and environmental isotopic studies. The results showed that karstic aquifer’s water level on the right side of the reservoir has very similar fluctuations with a difference between the minimum and maximum of 2.5 to 3 meters. The water level from the northern limb with a level of about 1625 decreases towards the spring in the southern limb with a level of about 1595 and a gradient of about 0.007. Also, spring discharge in the sought limb has the same fluctuation with three coefficients of recession curve. Recession curve coefficient α1 in the order of 10-2 indicates the intermediate flow (diffuse-conduit) make up 15% of the flow and the coefficients α2 and α3 in order 10-3 indicate the diffuse flow accounts about 85% of the aquifer flow. Hydrochemical and isotopic parameters of springs and boreholes also have low fluctuations. These variations for anions and cations are less than 20% and for Ec and acidity are less than 5%. The amount of environmental isotopes in springs and boreholes does not show any significant variations so that the standard deviation obtained from monthly acquired data is less than 1.2 per mil for δD and less than 0.2 per mil for δ18O. The amount of environmental isotopes shows that the source of springs is about 2300 meters and composed of heavy rainfall and snow in two limbs. Also, the isotopic composition of downstream springs is the average of the amount of isotopic value boreholes in the north and sought limbs showing that springs catchment area in left side (SPL) and right side (SP5) is recharged from both limbs of the anticline. Finally, the results of the studies show that the Jahrom-Asmari karstic aquifer on the right side of the reservoir is an aquifer with diffuse to diffuse-conduit flow. The aquifer is recharged through two anticline’s limb and mainly through the system of joints and fractures. The groundwater flows from the northern limb to the southern limb and is discharged into the springs downstream. In such a condition, the hydraulic connection between the anticline’s northern limb with the southern limb is exists. This connection is formed at the time of reservoir formation, between the reservoir and the lower springs of the dam axis with a higher gradient (around 0.037). Therefore, by the dam impoundment, the major seepage current in right abutment of the reservoir in the north limb of anticline towards sought limb and finally discharge in springs downstream of the dam axis