The Ongoing Drought Crisis in Spain
The drought has been a recurring topic over the past few years, taking center stage in the informational agenda due to the lack of rainfall and its myriad consequences. This ongoing situation begs the pressing question: how much water do we have left? The inquiry, however, leads to a troubling realization: we are not truly equipped to answer it.
What is abundantly clear is that our water reserves typically fall short of what official data suggests. This discrepancy arises from natural processes such as erosion and sedimentation , the ramifications of which have long concerned experts in the field.
Throughout their course, rivers transport small particles of rock and organic matter that tend to accumulate at specific points along their journey, whether on the riverbed, in delta formations, or in their meandering paths. Reservoirs are another prime location where water tends to “release” these particles.
The floors of reservoirs tend to accumulate silt . The primary problem this creates is the loss of the reservoir’s capacity. The greater the volume of the reservoir occupied by sediments, the less water it can store.
A second concern is that we do not have a precise understanding of the rate of sediment accumulation in each reservoir, as this can vary based on the characteristics of each watershed and reservoir. Without this knowledge, we are left in the dark about how much water remains .
The Weight of Sedimentation
Estimations regarding sedimentation—commonly referred to as siltation —vary significantly. A bathymetric study conducted in 2018 by the Tajo Hydrographic Confederation in the Entrepeñas and Buendía reservoirs suggested that sediment build-up was negligible.
Conversely, another bathymetric study, undertaken by the Segura Hydrographic Confederation , estimated that its reservoirs could have lost between 10% to 40% of their capacity due to this phenomenon. Notably, they highlighted the Lorca reservoir, built at the end of the 19th century, as being on the upper end of this spectrum.
Estimates for all Spanish reservoirs remain limited. A study encompassing 110 reservoirs indicated that the loss of capacity could be around 5% . José Luis Casamor and Antoni Calafat from the University of Barcelona cautioned that the uncertainty surrounding this estimate is quite high, given that the potential to extrapolate these results to over a thousand other reservoirs is limited.
This issue is one that experts have been warning about for years . For example, the study conducted in the Segura basin was carried out in 2017 , while the work by Casamor and Calafat was published in 2018 in the Tierra y Tecnología journal of the Official College of Geologists .
In a subsequent article published in 2018 in The Conversation , Casamor explained that the problem of sedimentation presents “expensive and complex solutions.” Cleaning the sediment from reservoir beds is a daunting task that necessitates emptying the reservoir, a process made even more complicated in older reservoirs.
Experts like Casamor advocate for preventative measures . These involve integrating knowledge about sediment accumulation during the design phase of infrastructure projects. One suggestion includes the addition of dikes upstream from reservoirs to catch sediments before they reach the reservoirs.
Additionally, proposals have emerged for upstream sediment control , which includes reforestation efforts. Plants help reduce soil erosion, thereby decreasing the number of particles that reach rivers and ultimately reservoirs. In this context, the phenomenon of rural abandonment has also been partially held responsible for the current state of affairs. Furthermore, wildfires contribute to sediment runoff into waterways, emphasizing that mitigating those effects can aid in lessening the problem.
As the water crisis continues to pose challenges, addressing sedimentation in reservoirs has become imperative for the sustainable management of water resources in Spain.