This report details the geophysical prospecting works carried out for hydrogeological purposes on a property located 19 km north of Tartagal, Santa Fe. The objective of the work is to locate areas with potential underground water storage with aptitude for cattle watering. The property has an area of approximately 13 km2.
Location
Figure 1 shows the location of the investigated site and Figure 2 shows the parametric transect. This site was chosen because it has the presence of groundwater in quality and quantity according to that required. In Figure 3, Figure 4 and Figure 5 the transects on which the exploratory studies were carried out are shown. The method implemented was that of tomography. electrical resistivity
Figure 2. Electrical resistivity tomography transect ERT 001 (parametric)
Figure 3. Electrical resistivity tomography transect ERT 002
Figure 4. Electrical resistivity tomography transect ERT 003
Figure 5. Electrical resistivity tomography transect ERT 004
The property has a group of reservoirs for the accumulation of rainwater. It has a hole on the access road to the house that is dry. According to the owner, other perforations made on the property illuminate water with high salinity, not suitable for livestock watering.
To calculate the network, a digital elevation model taken from the IGN website was used. The DEM has a resolution of 5m. Drainage network is shown in Figura 8.
Figura 8. Drainage network
It can be seen that the standard is at the highest levels locally. The drainage network is shown superimposed on it. The latter shows how surface water runs to the E and W of the property. Four sites of interest emerge from this network. They are indicated by circles superimposed on the image. They correspond to the closing points of the micro-basins where the underground water flow lines would be expected to converge, based on the hypothesis that the latter copy the surface flow lines.
ERT
Measurements were carried out using the GD-10 equipment from GEOMATIVE, using different methods for data collection (arrangements). The separation between electrodes was 10 m for a total of 24 electrodes for the ERT001, ERT003 and 48 electrodes for the ERT002 and ERT004. The line length used for the ERT001 and ERT003 scans was 230m while for the ERT002 and ERT004 it was 470m. The arrangements used were Wenner Alpha and Wenner-Schlumberger and Dipole-Dipole. For data interpretation and investment, the RES2DINV program was used. Below are the images of the tomographies, where Figure 13 and Figure 14 show the profiles of the real resistivity obtained vs depth, after the inversion carried out using the interpretation program for ERT001 and Figure 15 and Figure 16 show the corresponding to ERT002. The reiteration of measurements in different arrangements for each transect allows evaluating the interpretive homogeneity and the best performance of the software with the minimization of errors..
ERT models
Figura 9. ERT001, Wenner Alpha array.
Figura 10. ERT00, Schlumberger array.
Figura 11. ERT001, arreglo Wenner-Schlumberger array
Figura 12. ERT002, Wenner alpha array
Figura 13. ERT002, Wenner-Schlumberger array
Figura 14. ERT003, Wenner Alpha array.
Figura 15. ERT003, Wenner-Schlumberger array
Figura 16. ERT003, Dipolo-Dipolo array.
Figura 17. ERT004, Wenner Alpha array.
Figura 18. ERT004, arreglo Wenner-Schlumberger array
Figura 19. ERT004, Dipolo-Dipolo array
Figure 20, Figure 21, Figure 22 and Figure 23 shows, on a satellite image, the electrical resistivity models obtained.
ERT001
The tomography was carried out in order to determine the geoelectric characteristics that would correspond to the areas where there is a presence of groundwater with low salinity. It was carried out in the EW direction. The Wenner Alpha array reached a depth of exploration of around 40m while the Schlumberger and Wenner Schlumberger reached 48m. The error in the adjustment of the first model was 1.26% 1.49% in the second in the third it was 1.27%. Progressive 0 is to the west. In the images obtained using the three arrangements, it is observed, in general, that the behavior of the apparent resistivity is quite homogeneous. The site of interest, where there is a catchment work, corresponds to the progressive 190. At that site, the behavior of the variable in question reaches its maximum, around 10 ohm.m. This resistivity value could be due to the fact that the subsoil, in this sector, contains stored water with lower conductivity. The anomaly extends to depths of 24 m. From that depth, the image shows a very low resistivity behavior that would correspond to the brackish aquifer.
ERT002
The tomography was carried out in the SE-NW direction. The Wenner Alpha array reached an exploration depth of around 91.2m while the WennerSchlumberger reached 104.8m. The error in the adjustment of the first model was 1.37%, while that of the second was 1.76%. A two-layer behavior is observed. The first, with a thickness of around 13m, has average resistivity values, no greater than 4 ohm.m. The lower layer has low resistivities, with values less than 1.5 ohm.m. The brackish aquifer would be housed in this.
ERT003
The tomography was carried out in the SSO-NNO direction. The Wenner Alpha array reached an exploration depth of 39.6 m, the Wenner-Schlumberger reached 48 m and the Dipole-Dipole only 31.9 m. The error in the adjustment of the first model was 1.72%, of the second, 2%, while that corresponding to the third was high, 12.1%. A two-layer behavior is observed. Like TRE002, the first layer, with a thickness of around 13m, has average resistivity values, no greater than 4 ohm.m. The lower layer has low resistivities, with values less than 1.5 ohm.m. The brackish aquifer would be housed in this. In this transect, two points of interest were marked on the ground, an issue that will be discussed later.
ERT004
The tomography was carried out in the SW-NW direction. The Wenner Alpha array reached an exploration depth of 91.2 m, the Wenner-Schlumberger reached 104.8 m and the Dipole-Dipole only 24.9 m. The error in the adjustment of the first model was 2.9%, of the second, 5.7%, while that of the third was high, 11%. Again a two-layer behavior is observed. The first layer in this case is more heterogeneous, with varying thicknesses from 13 to 25 m. This layer has medium to high resistivity values, not greater than 7 ohm.m. The lower layer has low resistivities, with values less than 1.5 ohm.m. The brackish aquifer would be housed in this. In this transect, two points of interest were marked on the ground with stakes, an issue that will be discussed later.
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