Channeling the Past to Face the Future

The canal here, which will run about 1.6 miles, will bank enough water each year to supply more than 7,000 people. It is part of a system of amunas totaling some 32 miles that have been rehabilitated throughout the highlands outside Lima over the past several years.

This is one of numerous places throughout Peru where TNC and other organizations are working to restore traditional water-management systems, as well as developing new, nature-based approaches to increase water supply and improve water quality for both people and nature. Some of these projects, such as this one, help stabilize and augment water supplies for urban areas like Lima; others are aimed at providing cleaner water to small mountain communities.

In addition to restoring amunas, these organizations and local communities are rehabilitating traditional small-scale reservoirs and restoring native wetlands, which act like natural water filters and remove metals and other toxins.

They’re also improving livestock grazing practices, closing off sensitive grasslands, and restoring forests and grasslands, which increase the landscape’s sponginess and ability to absorb water. Together, these initiatives show the promise of new—and ancient—ways of using nature to make every drop count.

Traditional amunas restore water to Lima, the second-largest desert city in the world, more efficiently and at lower costs than dams 

On the steep mountainside above the Santa Eulalia, Jhonatan Pérez, a resident of the nearby town of Carampoma who leads the crew here, explains that rebuilding the amuna is also a way of reconnecting with the community’s lost history.

The trail of red spray paint leads toward the original site of Carampoma, which, five centuries ago, was a mountain citadel. Soon after their arrival in the early 1500s, however, the Spanish conquistadors forced the village’s native Quechua inhabitants to move to a site farther down the valley where they converted them to Christianity, and where the town of Carampoma remains today.

Rehabilitating the amuna, says Pérez, “is a way of reviving the customs and traditions of our community and ancestors.”

Twenty-five miles down valley, the town of San Pedro de Casta sits perched over the yawning gorge of the Santa Eulalia, as if clinging by its fingernails to the side of the mountain. People here have long maintained an especially strong connection with amuna culture, which is much more than simply a way of moving water around the mountains.

Wearing a weathered felt hat and with a “wallqui,” a traditional knit bag filled with ritual items, hung around his neck, Gregorio Lopez is a sort of living encyclopedia and keeper of the cultural flame.

He explains that amunas here are tightly intertwined with “el camachico”—what he calls “the ultimate democracy,” a pre-Incan form of community governance that was forced underground under Spanish rule and has largely disappeared elsewhere in the region.

As more cities find themselves running up against the limits of a water-short world, managers are often single-mindedly obsessed with improving efficiency: the don’t-waste-a-drop approach that drives water agencies around the world to ruthlessly chase down and eliminate leakage from their systems.

Amunas, which one set of researchers called “a 1,400-year-old indigenous infiltration enhancement system,” are literally designed to leak. Amunas capture water from mountain streams swollen with rainy season torrents, and then guide that water out across the landscape to the spongiest ground—exactly those spots where the most water will infiltrate into the aquifer below. 

By doing so, amunas intercept water that otherwise would run off straight down hillsides and streams, instead banking it as groundwater.

That process essentially turns aquifers into natural reservoirs that complement the dams and reservoirs at the heart of Lima’s water system. The aquifers then slowly release that water through springs farther downstream, parceling the water out over several months beyond the end of the rainy season. In effect, the system is a time-release mechanism, a way of stretching the rainy season’s bounty over a longer part of the year. 

“During the rainy season, you save water in the aquifer,” says Aldo Cardenas, TNC’s Peru water coordinator, “and then, after the dry season starts, that water comes out through the springs.”

This not only helps residents in Lima, but also ensures that mountain and aquatic ecosystems have water for a longer period of the year.

The use of amunas could also potentially reduce the need for new dams, thereby preserving stream connectivity for fish and other aquatic creatures and benefiting biodiversity.

A Lima-based organization called Aquafondo, established with the help of TNC and other partners, has overseen the on-the-ground amuna restoration work.

Funding for the effort has come from Backus, Peru’s largest brewing company, and GIZ, Germany’s international development agency, as well as from other large industrial water users such as Coca-Cola, PepsiCo and Caterpillar.

The Conservancy, for its part, has been monitoring the performance of the amunas after their rehabilitation.

The potential is significant. While small mountain villages like Carampoma and San Pedro de Casta are still able to supply their own needs from seasonal runoff and mountain springs, the amunas can create extra water storage to benefit Lima, farther down the watershed.

A 2019 paper by researchers affiliated with the Regional Initiative for Hydrological Monitoring of Andean Ecosystems (iMHEA), with support from a conservation organization called Forest Trends, estimates that if amunas were scaled up across the entire watershed from which Lima draws its supplies, they could increase the city’s dry-season supply by 7.5%.

In San Pedro de Casta, TNC is working to refine those estimates with meteorological and hydrometric stations, radar flow meters and fluorescent tracer dyes that, after being released into the amunas, reveal the flow path of water underground. Recently completed monitoring of some 12 miles of amunas near the town has shown that during the dry season, they provide 32% of the water available in the river.

During the 2023 rainy season, amunas in the area recharged 647 million gallons of water.

On average, that water remained underground for 66 days—and in some cases, for more than five months—before discharging to the river, thereby extending Lima’s dry-season supplies by an equivalent amount of time.

Water captured by amunas also comes at a much lower price than that from conventional steel-and-concrete infrastructure.

At TNC, Cardenas and his colleagues found that a unit of water recharged into the aquifer through an amuna costs about one-third of what a unit of water captured by a new dam planned for construction on the Santa Eulalia will.

How native reeds and bacteria help remove sulfuric runoff before the water reaches local communities

Some indigenous communities are facing a different water struggle: toxic pollution from glacier runoff.

About 150 miles north, in the Cordillera Blanca Range of the Andes, Kiara Aguirre looks serious and on point, her eyes shielded under a blue ball cap. She is an engineer with the Instituto de Montaña, which works with communities throughout the Peruvian Andes. Unlike the amunas outside Lima, the focus of this project is entirely on the local community called Canrey Chico.

As global warming accelerates, rapidly melting glaciers in the mountain headwaters are exposing underlying rock that is high in sulfur, which then oxidizes in the open air.

That creates highly acidic glacial runoff, which is also laden with toxic levels of metals like iron, aluminum, cadmium and arsenic. That orange-tinted witch’s brew then flows into local streams and rivers, where farmers and herders get the water upon which their crops, cattle and families depend.

“Compared with contamination from mine effluent, the concentrations are low,” Aguirre says. “But with so much livestock and agriculture here, it goes up the chain and accumulates in people’s bodies; the entire population of Canrey Chico is affected.”

But just upstream from the village of Canrey Chico, in a wooded glen alongside a river at over 12,000 feet, Aguirre shows off what may be a solution to the problem. A stainless-steel headgate diverts foamy orange water from the river, slows it and then gently guides it toward a series of tightly coiled meanders. Those twists and turns are planted with clumps of native reeds known as “totorillas” and are full of sulfur-hungry bacteria, through which the water takes a leisurely six-and-a-half-day journey of purification. There’s a contemplative air to the system, like some sort of aquatic Zen garden.

“These wetlands are nature-based systems that mimic natural processes and don’t require any chemicals,” Aguirre says, adding with a laugh, “It’s like a big gut.”

The idea originated with a local community member who noticed that water percolating through native wetlands emerged much cleaner. Built with help from residents and students and professors from the local university, the concept is decidedly low tech. And that, it turns out, is another part of its beauty.

“The Ancash region is full of glaciers, and in a few years, climate change is going to be a critical issue for a lot of communities here,” Aguirre says. “A lot of population centers are going to be affected by contamination like this, but they don’t have the money to carry out large-scale projects. These are effective, they’re cheap to implement, and they’re easy for the community to manage.”

The Instituto de Montaña is still refining the design of the water-treatment system and gathering data to assess the effectiveness of the approach, just as TNC continues to assess the effectiveness of the newly rehabilitated amunas outside Lima. But these kinds of low-tech solutions are taking hold throughout the Andes, and offering a path toward cleaner and more abundant water for both mountain communities and big cities.

Compared with more mainstream, engineering-heavy water management methods, “it’s a totally different approach,” says TNC’s Garcia. “But we’re seeing exciting things start to happen.”