Ancient Methods Could Increase Water Availability in Coastal Peru

According to a new study conducted at Imperial College London, 1,400-year-old methods can possibly increase the availability of water in Lima during the dry season.

Dwelling between the Andes Mountains and the Pacific Ocean, the people of Peru’s coastal area depend on surface water from the Andes for industry, drinking water, and crop and animal farming.

The geographical area, which includes Lima—the capital city of Peru—is usually overwhelmed with rain during the wet season; however, water becomes scarce just before the advent of the dry season.

Such factors, along with the rapidly increasing population of Lima, means it is difficult to supply water to the city’s 12 million residents during the months of May to October, which mark the city’s dry season.

Currently, researchers at Imperial College London along with their coworkers at the Regional Initiative for Hydrological Monitoring of Andean Ecosystems in South America have demonstrated that ancient water systems—which happen to pre-date the Incan Empire—can be revived to save wet season water for the dry spell, where it is badly required.

In order to achieve this, the researchers examined a water system in Huamantanga, Peru—one among the last of its kind available in the city.

Trickle effect

Water systems in coastal Peru are constantly stressed, making it difficult for the city to handle the growing demand.

The people of Lima live with one of the world’s least stable water situations. There’s too much water in the wet seasons, and too little in the dry ones. The indigenous peoples of Peru knew how to get around this, so we’re looking to them for answers.

Dr Wouter Buytaert, Study Senior Author, Department of Civil and Environmental Engineering and Grantham Institute, Imperial College London

In 600 AD, ancient Peruvian civilization constructed ponds and canals both around and within the mountains to divert surplus amounts of rainwater from source streams through rocks and onto the mountain slopes.

It would take several months for the water to travel through the canal and pond system and resurface downstream—just in time for the dry spell. In order to inspect this, the team examined one such system which is located in Huamantanga’s central Andean community.

Hydrological monitoring and dye tracers were used by the team to analyze the system from the wet to dry periods of 2014–2015 and 2015–2016. To better interpret the practice and help map the landscape, social researchers also worked with the local people of Huamantanga.

They eventually discovered that the water took approximately between two weeks and eight months to emerge again, with a typical time of 45 days.

Based on these time scales, the researchers computed that, if the systems are expanded by governments to meet the water demand of the present population size, then 35% of wet season water—same as 99 million m³ per year of water through the natural terrain of Lima—could be rerouted and delayed.

This might boost the availability of water during the dry season by around 33% in the initial months, and an average of 7.5% for the remaining months. Such an approach could fundamentally prolong the wet season, offering longer crop-growing periods and more amounts of drinking water for local farmers.

Reported in Nature Sustainability, the study is the first to comprehensively look at the pre-Inca system to find solutions for today’s problems. The study demonstrates how contemporary engineering solutions could be complemented by indigenous systems to ensure water security in coastal Peru, stated the authors.

With the advent of modern science, you’d be forgiven for wondering how ancient methods could apply to modern day problems. However, it turns out that we have lots to learn from our ancestors’ creative problem-solving skills.

Dr Boris Ochoa-Tocachi, Study Lead Author, Department of Civil and Environmental Engineering, Imperial College London

“Like many tropical cities, Lima’s population is growing fast—too fast for water reserves to keep up during dry seasons. Upscaling existing ancient infrastructure could help relieve Peru’s wet months of water and quench its dry ones,” stated Dr Buytaert.

Indigenous ingenuity

Human impacts tend to worsen the seasonal variability, which is a characteristic of coastal Peru. These impacts specifically include the melting glaciers that are induced by global warming. In addition, humans contribute to soil erosion, which makes the soil extremely weak to support dams that are sufficiently large to hold all the water. Furthermore, wet seasons are made wetter, and dry seasons are made drier as a result of climate change, making it even more urgent to implement effective water storage in Peru.

The uncertainty of the Earth’s climate’s future also makes it complicated to design and construct systems that are meant to last for many years in the days to come.

According to the authors, integrating classic structures, like smaller dams, with pre-Inca systems can possibly distribute the workload across techniques and boost adaptability in a fluctuating climate.

Because we can’t rely fully on one method, we must be open-minded and creative—but our study shows we have lots to learn from the way Peru’s indigenous population intelligently managed their landscape 1,400 years ago.

Dr Wouter Buytaert, Study Senior Author, Department of Civil and Environmental Engineering and Grantham Institute, Imperial College London

As of now, the team has examined only one system, and hence the outcomes of comparable work may probably vary across the coastal areas in Peru. Nevertheless, the study demonstrates an intense argument for employing nature-based solutions to boost water security, which presently is the leading water agenda, both globally and locally.

The researchers continue to inspect the region in an effort to learn more about how indigenous systems, practices, and knowledge can aid in supplying water to enormous urban populations residing in dry, water-unstable conditions. In doing so, the researchers are hoping to enhance the water security and resilience in coastal Peru to an unpredictable and fluctuating climate.

“This fascinating example of ingenuity within local communities shows the enormous potential of indigenous knowledge to complement modern science,” Dr Ochoa-Tocachi concluded.

The Natural Capital Project, CONDESAN, Alternativa NGO, AQUAFONDO, TNC, UK Research and Innovation, and the Natural Infrastructure for Water Security Project, and Natural Environment Research Council funded the study.

The study, titled “Potential contributions of pre-Inca infiltration infrastructure to Andean water security” by Boris F. Ochoa-Tocachi, Juan D. Bardales, Javier Antiporta, Katya Pérez, Luis Acosta, Feng Mao, Zed Zulkafli, Junior Gil-Ríos, Oscar Angulo, Sam Grainger, Gena Gammie, Bert De Bièvre and Wouter Buytaert, was published in Nature Sustainability on June 24^th, 2019.