Background and Objective :
Karst is a composite image of all the roughness, shapes, pores, and phenomena caused by water corrosion, above and below the surface, in various soluble geological formations, which cover about 15% of the world's exposed rocks. Despite the importance of karst areas in the past, today, the study, identification, spatial analysis and management of these areas are of very interest to geologists, hydrologists, hydrogeologists, eco-tourists, geotourists and environmentalists at various scales. Karst phenomenon also has a special place in various dimensions from the point of view of geology and geomorphology, because the causes and methods of dissolution processes and forms and their extension in rocks and minerals are of great importance to East Mazandaran, especially in the study area, is geologically one of the areas with karst process potential and has been less studied due to environmental conditions, especially vegetation and access roads. This study is focused on identifying karst areas and their extent using RS and GIS method in the Zalem-Rud Sari basin in Mazandaran province in northern Iran. In order to identify karst areas and physicochemical characteristics of existing aquifers, it was first necessary to identify karst areas and then assess their physicochemical status. In the first step, using Landsat, ASTER and SRTM satellite data, geological maps, weather information and field visits, factors affecting karstification such as rock types, Fracture lineaments, vegetation, climate, condition of the drainages and the slope of the topography are extracted. It should be noted that in this step, to obtain a better result, fuzzy logic and Hierarchical Analysis Process have been used. In the second step, in order to investigate the physicochemical condition of the aquifer, the chemical parameters of some springs are analyzed and the dissolution parameters, saturation indices, the origin of water-soluble components and the general flow system in the existing aquifers are determined.
Materials and Methods:
In this study, the composition and distribution of rock, based on field visits and georeferenced geological maps of one hundred thousandths of Behshahr and Sari, have been done. Three methods of manual, automatic and semi-automatic have been used to extract the lineaments due to fractures. In the manual method, the lineaments are highlighted and extracted by applying High Pass filters, PCA and the color combination of Landsat 8 satellite data. In the automatic method, the Segment Tracing Algorithm (STA) in PCI software is used. In the STA algorithm, linear pixels are identified based on the degree of gray difference and then converted to vectors based on RADI, GTHR, LTHR, FTHR, ATHR and DTHR parameters. The Normalized Difference Vegetation Index (NDVI) was used to detect and extract vegetation status on OLI sensor data from the Landsat 8 satellite. To generate DEM, photogrammetric techniques were performed on a pair of stereo images of ASTER sensor in Idrisi software based on parametric variables of external and external orientations and ground control points (GCPs). The topographic slope of the area has been calculated by DEM and based on the degree in GIS and its map has been prepared. Based on the weather data of the General Meteorological Department of Mazandaran Province, the weather condition is determined by the isothermal, isohyetal and isoevaporation curves and the type of weather is determined by the De Marton method.
Results and Discussion :
The result of the above activities has been the production of lithological maps, density and distance from fracture lineaments, density and distance from drainages, topographic slope, rainfall and vegetation. Due to the different criteria used in the generated maps and the need for a single, comparable and proportionate criteria for combining information layers, fuzzy logic has been used. In this case, all layers, except lithology, which has a definite boundary and is a function of Boolean logic, are fuzzy and then extracted as fuzzy layers in GIS. On the other hand, because the weight and effectiveness of the eight factors affecting the occurrence of the karst phenomenon are not the same, the Hierarchical Analysis (AHP) method has been used to determine the preference and prioritization of these factors. And the participation rate, in other words, the weight of each criterion with an incompatibility coefficient of less than one percent has been calculated in Expert Choice 12 software. Finally, by the weighted linear combination (WLC) method, fuzzy raster layers based on their effective weight are combined with Compromise Operator or Gamma and the karst distribution map is extracted with different probability coefficients in the study area. In the next step, in order to investigate the physicochemical status of the aquifers and evaluate the karst phenomenon, 18 springs with equal flow and more than three litres per second were selected and evaluated using SPPS, RockWorks2016 and PHREEQC2.6 software. In addition to extracting hydrogeochemical tables and graphs, the saturation index of various minerals has also been calculated.
The results of this study show that the karst phenomenon has the most spread in the central part and the lineaments resulting from fractures have played the most role in the formation of this phenomenon. The water type of these springs is calcium-magnesium bicarbonate and according to the Gibbs diagram, the role of aquifer rocks in determining the chemical composition of water is very clear. Also, the saturation indices of minerals and the type of flow in groundwater reservoirs are diffuse and diffuse-duct flows. To this research, the use of new remote sensing technology and GIS increases accuracy and speed and reduces costs in karst studies.
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