Document Type : Research Paper
Authors
1 Professor, Department of Earth Sciences, Faculty Natural Sciences, University of Tabriz, Tabriz, Iran
2 MSc Graduate of Environmental Geology, Department of Earth Sciences, Faculty Natural Sciences, University of Tabriz, Tabriz, Iran
Abstract
Introduction
The Goijeh Bel basin, with extensive outcrops of igneous, metamorphic, and sedimentary formations and adequate rainfall (342.2 mm annual precipitation), has significant potential for storing and transferring groundwater through fractured media. These hard formation units, located in elevated areas, can supply drinking water to Ahar city without the need for pumping stations. Most springs in the basin originate from hard formations, with their concentration in the center and north indicating the development of aquifers in these units. Overextraction of groundwater through wells and the limitation of alluvial resources have shifted water resource management toward utilizing hard formation water sources. This study investigates the quantity and quality of groundwater resources in the Goijeh Bel basin to identify methods for sustainable water management and assess their suitability as an emergency drinking water source for Ahar city.
Materials and methods
The study area is located 10 km southwest of Ahar city within the Aharchai River basin, which ultimately joins the Aras River. Remote sensing and GIS techniques, including the Analytic Hierarchy Process (AHP), Weighted Overlay, and Ordered Weighted Averaging (OWA) methods, were used for data analysis. Landsat 8 satellite images were processed to generate raster maps for the Normalized Difference Humidity Index (NDHI) and Normalized Difference Vegetation Index (NDVI). In the AHP method, criteria were ranked and compared pairwise, with weights assigned based on their importance. These weighted layers were overlaid to create a groundwater potential map. Fieldwork involved sampling five groundwater sources and Goijeh Bel River water, followed by hydrochemical analysis of eight major ions (Na⁺, Ca²⁺, Mg²⁺, K⁺, Cl⁻, CO₃²⁻, HCO₃⁻, SO₄²⁻), TDS, pH, SAR, %Na, and TH. Electrical conductivity (EC), dissolved solutes, and chloride ion concentrations were assessed to evaluate groundwater quality for drinking and agricultural purposes. Meteorological data from Ahar’s synoptic station over the past 20 years were also analyzed. The spatial distribution of springs was used to validate groundwater potential maps.
Results and discussion
Using AHP, Weighted Overlay, and OWA methods, groundwater potential maps were generated based on lithology, line density, elevation, humidity index, slope, drainage density, aspect, and vegetation index. The OWA method showed the highest agreement with spring locations, with approximately 50% of springs situated in areas of medium to high groundwater potential. Qualitative analysis revealed an increase in salinity and EC from upstream to downstream, with EC values ranging from 310 to 1,444 µS/cm. Chloride ion concentrations followed a similar pattern, suggesting a dominant role of sodium and chloride in groundwater salinity. Schuler’s diagram indicated that most groundwater in the basin is suitable for drinking due to the absence of pollutant formations such as salt, clay, or marl. These findings align with studies on hard and karst formations in western Urmia, which also report good-quality groundwater.
Conclusions
The southwestern part of the basin exhibits high groundwater potential. Validation of groundwater potential maps using spring locations confirmed the reliability of the OWA method. The groundwater quality assessment demonstrated increasing salinity toward the basin outlet, but most groundwater remains suitable for drinking. Watershed operations, such as biological measures or flood and sediment control structures, can enhance infiltration and aquifer recharge in the hard formations. To quantify aquifer potential and estimate extractable water volumes, geophysical surveys and exploratory drilling in high-potential areas are recommended.
Keywords
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