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TN474 : Groundwater exploration by modeling and interpretation of resistivity data and obtaining water potential maps by integration of available information using fuzzy logic method in GIS (case study of Damghan plain)
Thesis > Central Library of Shahrood University > Mining, Petroleum & Geophysics Engineering > MSc > 2014
Authors:
Habiballah Noroozi [Author], Ali Reza Arab-Amiri[Supervisor], Abolghasem Kamkar Rouhani[Supervisor], Mehdi Rahimian [Advisor]
Abstarct: Considering that Iran is situated in arid and semi arid regions and suffers the low amount of rainfall and volume of freshwater, exploration and management of groundwater resources in Iran are significant. In this research, electrical resistivity sounding method using Schlumberger array has been applied for exploration of groundwater resources in Qusheh area of Damghan, located in eastern part of Semnan Province. For this purpose, resistivity sounding surveys with maximum distance of current electrodes of 1000 meters have been carried out on 40 sounding points along 8 lines in the area. Then, modeling and interpretation of the acquired resistivity sounding data have been made using standard and auxiliary curves and also VES, IX1D, IPI2WIN and RES2DINV software packages. As a result, the resistivities, thicknesses and depths of subsurface laxyers including the resistivity, thickness and depth of water-bearing formation or aquifer have been determined in each sounding location and also, the approximate aquifer extent has been estimated along each survey line. The interpretation results indicate that the water-bearing laxyers having resistivities of higher than 40 ohm-meters possess suitable quality groundwater. In fact, more resistivity value of the water-bearing laxyer, the higher quality of its groundwater will be, and vice versa. As the resistivity of the water-bearing laxyer in some sounding points, especially in central and southern parts of the area, is low, we can conclude that either the alluviums containing groundwater in these parts of the area have been formed of fine sediments or the quality of the groundwater is low. The bedrock elevation in western parts of the area as the surface elevation is high, it decreases towards east of the area. Least variation of the bedrock elevation is seen in north-south direction as slight variation is seen in the thickness of the alluvium above the bedrock in this direction. However, some variations in the bedrock elevation and alluvium thickness in southern parts of the area are observed due to the existence of a hidden fault with southwest-northeast trend in this part of the area. In this research, geographic information system (GIS) has been used for management of resistivity data and making suitable decisions for determination of high potential groundwater zones. In this regard, first, the quantities of depth, thickness and resistivity of water-bearing formation or aquifer, obtained from the interpretation results of the resistivity sounding data in each sounding location, have been digitized, classified and weighted with the help of ArcGIS software package. As a result, the evidential map for each of the above quantities in the study area has been obtained. Considering the relative importance of each of the above three quantities in the groundwater exploration, different weighting values were assigned to the three quantities. Consequently, groundwater potential maps in GIS environment were obtained using index overlay and fuzzy logic integration methods. In the final fuzzy exploration map obtained using fuzzy gamma operator of 0.95, the higher fuzzy values were observed in northeast and southwest parts of the area, indicating that these parts contained higher groundwater storage (considering their relatively thick water-bearing laxyers), more suitable groundwater quality (considering higher resistivity of water-bearing laxyers) and more accessible groundwater (considering lower depths for the water table). Finally, investigation of final exploration maps and geological information of the area, and also, considering the opinion of the relevant expert, it was suggested to drill the limits around some sounding points in northeast and southwest of the area for groundwater extraction wells
Keywords:
#Groundwater #Resistivity #Geographic information system (GIS) #Fuzzy method #Water potential map #Qusheh Keeping place: Central Library of Shahrood University
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