The future professionals of the hydrogeology, who are nowadays been formed in our universities must be prepared to use techniques that currently are not very utilized in hydrogeological studies. In many universities, Geophysical Prospecting is included in the programming of the subject of Hydrogeology as an auxiliary technique in the hydrogeological studies. Nevertheless, in many cases, training teaching of this issue can not be imparted due to the need of a series of instruments very expensive and not commonly available for teaching in the universities. We propose here an experience developed in the Granada University (Spain) in which, after knowing the changes in soil use that trigger a classical hydrogeological problem, the students complete their analysis with the combined application of two different geophysical techniques.
Our students know that marine intrusion is the most serious problem facing coastal aquifers that are exploited for use and that it is also an excellent indicator of the state of the aquifers resources.
After analyzing deeply the theoretical essentials of saltwater intrusion and to know the hydrogeological characteristics of one aquifer, we proposed the combined application of two complementary geophysical techniques as an effective method for locating the saline wedge. On one hand, Time Domain ElectroMagnetic soundings are the most reliable geophysical method for determining low-resistivity zones that usually correspond to the presence of saltwater, although in some cases low resistivities may be due to the properties of the substrate. On the other hand, gravimetry allows a precise determination of the depth of the aquifer basement, thus resolving the above uncertainty. Information provided by the lithological columns from boreholes has also allowed the students to get great precision in the calibration of the results from both techniques.
This methodology has been applied to the Motril-Salobreña detrital coastal aquifer, which has had no problems of marine intrusion to date. Nonetheless, the students know that changes in soil use brought about by housing developments, golf courses, and a proliferation of hothouse agriculture comprise significant shifts in aquifer use. In addition, the construction of a dam, which is drastically reducing the main recharge of the aquifer (the Guadalfeo River), makes it likely there will be profound hydrogeological changes. After this previous knowledge, the students are expectants to try to delimit the extent of the saline wedge as a fundamental step towards quantifying the effects of both the dam and the changes in soil use.
Our experience makes clear that the application of different techniques to tackle a previously known problem reveals as a stimulating mechanism of the creativity of the students. In this way they became more receptive and flexible to put into practise in the future new methodologies maybe now unknown for them during their academia period.