Past innovations for future resilience: Hydrogeological appraisal of La Valduerna’s Ag-MAR system
This study validates the La Valduerna region's centuries-old agricultural managed aquifer recharge (Ag-MAR) system, demonstrating through hydrogeological modeling that traditional infiltration channels (zayas) are a critical, cost-effective nature-based solution for overcoming natural recharge deficits and ensuring sustainable groundwater availability for irrigation.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
In many parts of the world, farmers face a difficult rhythm: rain falls heavily in the winter, but crops need water in the scorching heat of summer. Nature often struggles to bridge this gap, leaving rivers dry and soil parched when it matters most. To solve this, people have long looked to the ground beneath their feet. Aquifers are vast, underground layers of sand and rock that hold water, acting like natural sponges. While we often think of these as static reservoirs, they can be refilled. This process, known as managed aquifer recharge, involves intentionally guiding surface water into the ground to store it for later use. When farmers do this using their existing fields and irrigation channels, it is called agricultural managed aquifer recharge. It is a way of turning the landscape itself into a storage tank, capturing excess winter flow to survive the dry months. As climate change makes weather patterns more erratic, finding simple, low-cost ways to keep these underground reserves full has become a critical question for water security.
In the La Valduerna region of northwestern Spain, this concept is not a new experiment but a centuries-old tradition. For generations, local farmers have used a system of unlined irrigation channels, locally called zayas, to divert water from the Duerna River into their fields during the wet season. As the water flows through these open channels and floods the soil, it seeps down, recharging the shallow aquifer below. Later, when the river runs low in late summer, farmers pump this stored groundwater to water their crops. However, a conflict arose in 2017 when water authorities restricted the use of these channels to the official irrigation season starting in April, effectively banning the winter diversions that had historically filled the underground reservoir. Farmers argued that this policy was draining their water security, but without hard data, the debate remained stuck between tradition and regulation.
A team of researchers from the Spanish Geological and Mining Institute set out to settle this question with a comprehensive look at the land itself. They combined old maps, modern satellite images, and field measurements to build a detailed picture of the underground world. They dug into historical records, finding that these channels have been in use since at least 1433, with some evidence suggesting the system may be even older, rooted in the Islamic period of the Iberian Peninsula. To understand how the water moves, the team constructed a three-dimensional model of the aquifer, piecing together data from nearly 180 wells and electrical surveys to see the shape and depth of the water-bearing sand and gravel layers. They also built a computer simulation of the rivers and the rainfall to predict how much water was available and when it could be safely diverted without harming the river's ecosystem.
The results painted a clear picture of a system that is working, but is currently being held back. The study found that the aquifer is relatively small, holding between 9 and 12 million cubic meters of water. Natural rain alone is not enough to keep it full; it only adds between 1 and 3 million cubic meters a year, while the farmers need between 6 and 8 million cubic meters to irrigate their crops. This gap means that without the help of the zayas, the groundwater would run dry. The researchers measured the system in action during the spring of 2024. By diverting water through the three main channels for 43 days, they observed the water table rise by nearly half a meter across the entire area. This single event added about 1.5 million cubic meters of water to the underground storage, proving that the channels are highly effective at moving water from the river into the ground.
The computer simulations offered a path forward for the future. The models showed that if the farmers were allowed to use the channels earlier, starting in January instead of April, they could capture significantly more of the winter surplus. Alternatively, adding new channels to the system could double the amount of water recharged each year. Crucially, these simulations indicated that such changes would not harm the river's ecological flow, the minimum amount of water needed to keep the river healthy for fish and other wildlife. The study confirms that the zayas system is a robust, nature-based solution that has sustained the community for centuries. It is a simple, gravity-driven method that uses local materials and existing infrastructure to solve a complex modern problem. The authors conclude that recognizing and supporting these ancestral practices, rather than restricting them, is essential for ensuring water resilience in a changing climate. The data suggests that by working with the natural rhythm of the seasons and the land, communities can secure their water future without expensive new technology.
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