The study is focused on desert areas of coastal Peru which are highly depended on the water streams deriving from the Andes. A major issue is that those streams do not have a constant water flow and therefore, they do not provide water supply during the dry season. To address this problem, ancient engineers constructed the aforementioned system of canals that stored the excess amount of water in natural springs.
The canals that were made out of stone and soil, were less permeable than the natural ground and were capable of carrying large amounts of water to the springs. “Water is stored in the soils and travels much slower beneath the surface than it would as overland flow,” Dr. Boris Ochoa-Tocachi, a Post-doctoral Researcher at London's Imperial College, stated.
Currently, most of those canals are abandoned. However, there are still some local communities that use 11 of them to provide 65 springs and 14 lakes with water supply. Moreover, some local organizations took the initiative to optimize the canals' performance mostly by using concrete to decrease their permeability.
Authors examined the performance of one canal that is still operating to find out that about 50% of the rainfall water is captured. Thus, they concluded that the system is still highly effective, at least for small communities.
The ultimate purpose of the researchers is to implement a similar technique to resolve the water shortage issue in big cities with large population. Currently, Lima, the capital city of Peru, needs an excess of 43 million m3 to satisfy its water demand during the dry season and, therefore, the ancient approach could tackle the issue.
Researchers simulated a canal system connected to the Rimac River basin that provides water to Lima and conducted computer analyses. The findings show that, by applying the system, the water flow will increase by 7.5% during the dry season on average. However, the water supply will not be distributed evenly. The first 2 months will experience a 33% increase while the following period will be slightly affected. “We observed that the water volumes will follow a curve that peaks after two months and is sustained even eight months later. The mean residence time of water inside the soils is 45 days, which means that if a unit of water is infiltrated in day 0, half of this unit would come out within the first 45 days, and the other half will come out after 45 days, but for as long as 10 months after the initial infiltration. This means that water will emerge unevenly (more water during the early months and less water during the later months),” Dr. Ochoa-Tocachi explains. According to the results, 99 million m3 of water will be diverted to the Rimac river by implementing the canal system.
However, according to Dr. Ochoa-Tocachi neither local authorities nor the Peruvian government are ready to invest in the canal system. “Although local NGOs (Non-governmental organizations) have become interested in restoring some of the canals, Lima's water utility SEDAPAL is still more reluctant to invest in this type of infrastructure,” he commented.