#07 | Is it possible to know if a territory is rich in groundwater without ever setting a foot there?

Author: Damián Sánchez (Cetaqua)

Traditionally, the way to know if a territory -usually an unexplored or remote one- has got groundwater and, consequently, we can take advantage of them to cultivate crops or settle a town, for instance, has been through fieldwork carried out by a geologist or, to be correct, by a hydrogeologist (i.e., the geologist specialised in the study of groundwater).

However, life changes and now things can be done differently. And this is possible, especially because of the -enormous- development of satellites, remote-sensing data, and geographic information systems. If you do not know what I am talking about… just keep reading.

Assessment of groundwater potential

Well, in recent years diverse methodologies for evaluating the potential occurrence or existence of groundwater have been proposed. These methodologies are not so useful in developed countries, such as Spain, because there are already very detailed maps and cartography showing the location and characteristics of aquifers. However, these methodologies are exciting for more challenging territories, with little or no information on groundwater, such as dry areas (deserts, for instance), mountainous regions where access is not possible, or remote areas located far away from populated zones.

How do these methodologies work?

The basis of all these techniques aiming at identifying areas with high potential to store groundwater is the existing relationship between groundwater and other variables for which we do have available information.

Maybe this is still a bit difficult to understand…let me explain myself with an example: when the terrain is flat, i.e., when the slope is around 0%, rainwater does not usually flow away, but it typically infiltrates and, consequently, the probabilities to find groundwater is higher. On the contrary, in very mountainous regions, with steep slopes, rainwater tends to flow through rivers instead of infiltrating; therefore, the probabilities to find groundwater are fewer. And, thanks to satellites and remote sensing, we happen to have topographic information of the land surface ¡for the entire planet!

What other variables are used to identify groundwater potential zones?

You can find below a selection of the most frequent variables used by these methodologies to identify areas with a high potential to gather groundwater resources:

  • Geomorphology: Geomorphology studies the origin and evolution of topographic features. Alluvial plains and terraces will show more potential than mountain reliefs or cliffs, for instance.
  • Slope: It works very similar to the previous one: The flatter the terrain, the more likely it is to find groundwater.
  • Drainage density: A drainage network well developed indicates that rainwater mostly flows through rivers and streams and, consequently, the probability to find groundwater is smaller.
  • Land use: When land is covered with forests or shrubs the groundwater potential is higher than when it corresponds to arid zones, for instance.
  • Vegetation development: It can also be established a relationship between the development degree of vegetation and groundwater. On one hand, because plants’ leaves and roots contribute to keeping rainwater, then increasing the probabilities of infiltration; and, on the other, because some deep-rooted plants obtain a significant portion of the water they need directly from aquifers (they are called phreatophytes).

Final result

The final result of these techniques consists of a map of the area under study showing, either with a series of scores or with colours, the potentiality to find groundwater: Very low, Low, Medium, High or Very high, for example.

 

This map is obtained through the overlay (superposition) of the different variables (layers) used, assigning a different weight or influence to each of them. And this is done using specific software usually known as Geographic Information Systems (GIS), such as QGIS or ArcMap, among others.

Although the position of a new well, for example, will probably require a visit to the field, these methodologies represent a rapid and very economical way to make a first selection of the most interesting areas, in which we should start the study.