RESULTS AND DISCUSSION
Electrical resistivity measurements were conducted at 41 sounding points in the study area in order to determine resistivity variation with depth for indentifying fresh and saline water in this area. The results of resistivity measurement are presented into three example groups of the resistivity curves, which represent in western, middle and eastern parts of the study area (Figures 4, 5, and 6). These resistivity curves obtained from present work can be classified into four types such as two-layer, three-layer, four-layers, and five-layer. Most types of these curves are represented in three earth layers in this study area. Generally, apparent resistivity is greater than 100 ohm-m at small current electrode spacing and decreases to 2 ohm-m at larger current electrode spacing. However, at some sounding stations, apparent resistivity of the ground shows a gently increase at very large electrode spacing.
The resistivity sounding curves located at S-16, S-17, S-19, S-23, S-33, and S-34 (Figure 4) are examples of resistivity curves are represented in the western part of the study area. Three-layered and four-layered earth was modeled from these curves with the following parameters; resistivity range from 45 to 295 ohm-m and its thickness range from 1.5 to 2.9 meters, resistivity range from 15.9 to 94.4 ohm-m and 2.8 to 90 meters thick for the second layer, and resistivity of 8 to 69.4 ohm-m and 11.8 to 113.6 meters thick for the third layer and resistivity of the bottom layer range from 18 to 1345.8 ohm-m.
The resistivity curves located at S-2, S-7, S-8, S-9, S-11, and S-35 (Figure 5) are represented in the middle part of the study area. Three-layered and four-layered earth was modeled from resistivity curves with the following parameters; found low resistivity less 8 ohm-m and 1 to 43.9 meters thick at S-7 and S-35, whereas found low resistivity less than 10 ohm-m at large current electrode spacing from these curves, except S-2, low resistivity may be caused by thick salt deposit in this area.
Fig. 4. The VES interpretation with calculated data fitting observed data, which obtained from western part of Champhon District (S-16, S-17, S-19, S-23, S-33, and S-34)
The resistivity sounding curves located at S-21, S-26, S-27, S-30, S-31, and S-32 (Figure 6) are represented in the eastern part of the study area. Three-layered and four-layered earth was modeled from resistivity curves with the following parameters; high resistivity is greater than 100 ohm-m and 0.7 to 4.8 meters thick for the top layer, resistivity varies from 32.2 to 514.4 ohm-m with thickness ranges 5.5 to 47.1 meters for the second layer, except at S-2 found resistivity 6.5 ohm-m and 9.2 meters thick for this layer and resistivity decrease to 10 ohm-m for the bottom layer, except for resistivity curve at S-2.
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