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Ancient Irrigation Systems Could Help Peru on Water Security

Conceptual representation of how the pre-Inca infiltration system works. Water is diverted during the wet season using canals that transport surplus water during the wet season to high permeability zones. Water penetrates the soil and emerges in downstream springs after weeks or even months, which provides water during the dry season. Credits: Ochoa-Tocachi et al., Nat. Sustain., 2019.

Between the Pacific Ocean and the Andes mountains, Peru’s coastal region relies on surface water from the Andes for drinking water, industry and animal and crop farming.

This region, which includes the 12 million residents of Lima is often overwhelmed with rain in the wet season. However, by the time the dry season comes, water is scarce. With a rapidly growing population, the city struggles to supply water between May and October.

Now, Imperial researchers and their colleagues at the Regional Initiative for Hydrological Monitoring of Andean Ecosystems in South America, have outlined how reviving ancient water systems could help save wet season water for the dry season.

The indigenous peoples of Peru knew how to get around this, so we’re looking to them for answers“, says senior author Dr Wouter Buytaert. “Upscaling existing pre-Inca systems could help relieve Peru’s wet months of water and quench its dry ones.”

How does it work?

Ancient Peruvian civilisations in 600 AD created systems within mountains to divert excess rainwater from source streams onto mountain slopes and through rocks.

The water would take some months to trickle through the system and resurface downstream—just in time for the dry season.

They found the water took between two weeks and eight months to re-emerge, with an average time of 45 days. From these time scales, they calculated that, if governments upscale the systems to cater to today’s population size, they could reroute and delay 35 per cent of wet season water, equivalent to 99 million cubic metres per year of water through Lima’s natural terrain.

This could increase the water available in the dry season by up to 33 per cent in the early months, and an average of 7.5 per cent for the remaining months. The method could essentially extend the wet season, providing more drinking water and longer crop-growing periods for local farmers.

Beyond this fascinating example of ingenious problem-solving, our research shows the enormous potential for indigenous knowledge and rural science to complement modern science“, concludes Dr Buytaert.


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