By Jay Landers
As a country, Peru is rich in freshwater, but the geographical location of those resources makes them largely unavailable to most of the country’s growing population. Unfortunately for South America’s fourth-most populous nation, nearly all of Peru’s freshwater is present in Amazonian rainforest located to the east of the towering Andes Mountains. By contrast, most of the country’s residents are found in the mountains or along the arid coastal plain to their west that borders the Pacific Ocean.
This mismatch between water resources and population is felt acutely in Lima, Peru’s capital city, which struggles to provide adequate supplies of drinking water to its 11 million residents. At the same time, Andean villagers are experiencing growing water scarcity, as the mountain glaciers that supply the runoff they have relied on for generations continue to shrink.
In a unique historical twist, one of the solutions that could help alleviate the water concerns of both urban and mountain dwellers alike involves rehabilitating ancient systems known as amunas that are used to capture and store water underground high in the Andes. (In Quechua, the language of certain Indigenous peoples of Peru, amuna means “to retain.”)
In recent years, the Peruvian nongovernmental organization Aquafondo has led these rehabilitation efforts, helping Andean villagers ensure they have enough water to sustain their livelihoods during Peru’s dry season.
Meanwhile, a growing body of research indicates that restoring the amunas also will improve the outlook for Lima’s drinking water supplies.
More than 1,000 years ago, the Huari people occupied the Andes Mountains in what is now modern-day Peru. In Chapter 6 of her 2022 book Water Always Wins: Thriving in an Age of Drought and Deluge, author Erica Gies described how the ingenious Huari used amunas to solve their need for water in the region’s dry season:
“They built canals to divert high flows from alpine streams during the rainy season and spread it across porous basins, where the water infiltrated into the ground and later emerged from springs at lower elevations. Because water moves more slowly underground through sediment than it does running on the surface, this strategy allowed people to harvest the water for irrigation in the dry season weeks and months after it fell from the sky.”
To prevent water from flowing straight down the hillside, amunas often include walls along their lower edges. Made principally of such local materials as rock and clay, the walls typically stand about 60 cm tall.
Over time, the amunas largely fell into disrepair, though some remain intact and continue to be used by communal farmers in the Andes. Gies described one such amuna as a “canal about two feet wide and a couple of feet deep (that) winds like a sinuous snake along the contour of the hills for almost a mile.”
For its part, Aquafondo is working with the communal farmers to repair and restore the decrepit amunas in the hopes of boosting underground water supplies in the region, supplies that in some cases could find their way downstream to thirsty Lima.
Working with villagers
Aquafondo began repairing amunas in 2012 as part of a partnership with the conservation organization The Nature Conservancy and the U.S. Agency for International Development, says Pamela Quino, the technical coordinator for Aquafondo, who spoke to Civil Engineering Online by means of a translator.
By the end of 2022, Aquafondo had overseen the restoration of 23 amunas totaling 34 km in length. Located in four watersheds, these amunas range from 305 m to 8.4 km in length, Quino says.
Aquafondo works closely with the villagers to locate amunas, some of which may require extensive repair efforts. In some cases, only a “trace” of an amuna is apparent, Quino says, while in other cases the structures require only minor repairs. Typically, a group of about 25 people is needed to restore a 1 km long section of amuna.
Much rehabilitation work remains to be done. Mapping conducted by The Nature Conservancy in 2018 found 25 amunas totaling 67 km in length, Quino says. However, more of the systems are known to exist because villagers have informed Aquafondo of additional amunas that were not included as part of the mapping effort, she notes.
“Our goal for this year is to restore at least 8.8 km,” Quino says. Next year, in 2024, Aquafondo aims to restore a further 14 km at least, she says.
Following the restoration efforts, local springs are providing more water during the dry season, enabling villagers to engage in agriculture and raise cattle when water is most scarce, Quino says. Hydrological monitoring conducted in 2019 confirmed that water from the springs had originated in the amunas, Quino says. “It was the same water.”
Meanwhile, the increased moisture in the hillside facilitates the growth of vegetation that, in turn, helps control erosion on the steep slopes.
Ultimately, restoring the amunas is expected to boost local infiltration on a major scale, as shown by a study from the Water Research and Technology Center at the University of Engineering and Technology, in Lima. For the study, researchers conducting hydrologic monitoring determined that, on average, 1 km of amuna contributes more than 225,000 cu m of water per year to groundwater supplies, Quino says.
Based on this estimate, the amunas rehabilitated by Aquafondo to date have an infiltration potential ranging from 68,000 to 1.9 million cu m/year, according to the organization’s website.
If all 67 km of known amunas were to be restored, a “potential water benefit” of 15 million cu m/year could be realized, according to the website.
Based on the results of a previous study conducted by the World Bank to evaluate the benefits of amuna restoration, Aquafondo has determined that approximately 20% of the infiltrated water eventually will make its way to one of the rivers that supplies drinking water to Lima.
In certain years, the percentage available to Lima might even increase from that if local use of the springs declines, Quino says. “The goal is water security,” she says.
This article first appeared in Civil Engineering Online.