Could This Ancient Water Tech Save Lima?
WHY YOU SHOULD CARE
This 21st-century water problem might have an ancient fix.
By Wesley Tomaselli
From afar, they appear to be silvery serpents zigzagging down the Andean highlands. Up close, though, they turn out to be ancient stone ditches. Known as amunas, these vestiges of pre-Incan technology are now being restored and put back into use. And they might even save a city just downstream: the Peruvian capital, Lima, where 10 million people dwell in the middle of a coastal desert.
As climate change melts glaciers and globalization draws people to megacities, water resources are being subjected to enormous stress. Perhaps nowhere is this more visible than Lima. Here, only 1 in every 10 inhabitants has access to potable water. The rest are thirsty, and often tired from hauling water jugs across town. That’s where the amunas come in.
Well before 1533, when Spanish invaders conquered the Incas, indigenous peoples had engineered a canal system to manage the extreme disparities in water access along the arid coast of what is now Peru. The system is twofold: diversion canals, built from impermeable stone, and permeable infiltration canals that allow water to seep into the subsurface during the rainy season.
The water is then directed from the amunas to fill water holes where it can be harvested during the dry season, explains Mariella Sánchez, director of Aquafondo, a water fund established in 2014 to help with rehabilitation of the ancient system. The system also prevents erosion, which is more likely to occur during the dry season.
Lima is the second-largest city in the world located in a desert.
Aquafondo and other organizations are recovering miles of the centuries-old technology, with some 5.6 miles already revived. And experts are toying with the idea that amunas could inform new hydro technologies for supplying Lima with water and saving what some experts believe is a city on the verge of a crisis.
Lima is the second-largest city in the world located in a desert, right after Cairo, says Hugo Contreras, the Nature Conservancy’s director of water security for Latin America, and “65 percent of the population lives on the coast where only 2 percent of the water is.”
Changes in climate conditions can disrupt hydrological cycles. At the same time, people around the world are increasingly living in urbanized environments where access to basic services like sanitation and potable water is limited. Lima water and sewage utility Sedapal estimates that unless investment increases and the city expands its water system, demand for potable water will outstrip supply by 2030.
Contreras hopes that ancient technologies like amunas and modern methods can meld to provide water security solutions and keep Lima’s water crisis at bay. The Nature Conservancy is currently testing the viability of amunas as supply systems by measuring water volumes during the dry season. The organization has already discovered that amunas extend the period that water is available during the dry season by months. The Peruvian government is also getting behind the restoration. A $24 million package for investment in natural infrastructure, which would include rehabilitation of the ancient ditches, is expected this year.
“[Our team] is measuring the impact in order to see how much water we can bring to the city of Lima,” says Contreras.
Indeed, magnitude presents a challenge. Sánchez cautions that the network of canals may not be as scalable as some would like to believe. “The amunas weren’t originally built so much for scaling and satisfying water for large populations,” she explains, adding that amunas are unlikely to be the only solution. In fact, a desalination plant on the coast of Lima is already under construction.
That’s why Contreras insists that ancient ways of addressing water need to be combined with modern technologies for the scale of a megacity like Lima. “The question for me is how can we turn this traditional technology into modern technology, where you try to use nature as part of modern technology,” he says. “If you could have a hybrid, I think that’s where you have the most to gain.”