[Column] Coastal aquifers: the importance of caring for a unique resource

Friday, 17 de June

By Daniele Tardani, researcher at CEGA and associate professor at Universidad Estatal de O’Higgins (UOH).

As we all know, the drought is affecting us seriously in many aspects, and one of them is that the lack of rain is reducing the possibilities of supplying water for human consumption. In addition, high temperatures, caused by climate change, cause a significant increase in the evaporation of this resource, which further complicates this problem. Therefore, the proper use of this element and the care of the reserves is fundamental, we are talking not only about the water we see on the surface but also that which is underground.

And, at this point, subway aquifers are of vital importance. They contain a high percentage of the water we consume and are fundamental in coastal areas, where surface water resources are saline and therefore unusable for irrigation, human consumption and many industrial processes.

In the past, cities were mainly supplied by surface water located in lakes, rivers, lagoons, etcetera. But nowadays this is practically impossible, because it is mostly polluted, except in very pristine places such as Patagonia. Thus, it is mainly used in dams and in some industrial activities.

So, everything related to food production, drinking water supply and crop irrigation, in many parts of the country and the world, is mostly done through groundwater. In a UNESCO report of the year 2022, it is mentioned that 70% of the world’s groundwater extraction is used for food production. This water is less evident, it infiltrates the ground by precipitation in the Andes Mountains and moves slowly below the surface in porous or fractured media until it reaches the ocean, where, like surface water, it flows into the sea. A priori it is difficult to imagine what these subway aquifers are or what they look like: a good approximation is to think that we have a box full of rice and that in the empty space between each granite there is liquid water that is able to move and accumulate, and that we can take advantage of.

We know that in the context of drought, such as the one we are experiencing, the recharge of these aquifers is lower due to the decrease in precipitation, so conscious water management is increasingly important. These groundwater reserves are extremely vulnerable, both from the point of view of the reduction of this stock and the risks of contamination. In coastal areas, this resource is even more vulnerable because fresh water is directly in contact with saline water and this can lead to a process called saline intrusion. This process is caused by the entry of seawater into freshwater aquifers and has natural causes such as rising sea levels, or anthropogenic causes, such as excessive exploitation of groundwater, which leads to a decrease in its level and favors the entry of saline water. If this occurs, water quality degrades and its use becomes impossible for both irrigation and human consumption.

Chile is a country that has 6,000 kilometers of coastline and this is home to most of the large cities, such as Viña del Mar, Valparaíso, Concepción, Puerto Montt, Valdivia, La Serena and Antofagasta, among others.

In general, population density is significantly higher in coastal areas than in continental areas and there is a constant trend of migration to the coast, associated with global demographic changes. The growth and urbanization rates of the coastal population are outpacing the demographic development of the interior, driven by rapid economic growth. In China and Bangladesh, for example, the population in the coastal zone grew at about twice the national growth rate between 1990 and 2000. In Chile, the last census showed how the urban dynamics of cities such as Antofagasta and Puerto Montt, accompany the communes of Santiago in the outposts in terms of demographic expansion.

In a social context of world population growth and specifically in coastal areas, groundwater is a fundamental and irreplaceable resource in relevant aspects of our lives. Therefore, it is of vital importance to have a thorough knowledge of the aquifers, their recharge processes and how much water they can provide without causing irreversible damage and to protect them from contamination phenomena such as the aforementioned saline ingression.

Although the State has a register of surface water reservoirs and subway aquifers, there is no clear public policy on the management of the water we have underground. In other words, there are partial registries of the wells drilled in each aquifer, rights are granted to extract water from these wells, but the State does not have the capacity to answer the question of how much water can be extracted from an aquifer without causing irreversible damage in a context of climate change. This means that there is no capacity to adequately manage the resource. Having recent and complete studies on these aquifers in their current state and their future projection is the great challenge in the country for the short term.

You can read the publication in Qué Pasa here.