Amunas of Huamantanga & Huarochirí — Reviving Pre-Inca Infiltration Canals for Lima's Dry-Season Water (Peru)

Amunas (Quechua for 'to retain'; Spanish mamanteo, 'breastfeeding') are pre-Inca canals that divert wet-season stream water from about 3,800 m onto rocky hillslopes so it infiltrates and re-emerges weeks later in downslope springs. A 2019 Nature Sustainability study by Imperial College London, CONDESAN, SUNASS, FONAG, Forest Trends and PUCP partners examined one of the last intact systems, in the community of Huamantanga (Canta Province, c. 3,300 m).
Using tracer tests, the authors found infiltrated water stayed underground about 45 days on average before resurfacing, lengthening and stabilising dry-season spring flow. Extrapolating to Lima's source-water areas, they estimated that restoring such systems could delay about 99 million m³ of streamflow per year and raise dry-season flows by roughly 7.5% on average — against a dry-season deficit of about 43 million m³ and about 330 million m³ of existing artificial storage. This scale-up is a modelled estimate, not a measured outcome, and the authors frame amunas as a complement to grey infrastructure.
Aquafondo, the Water Fund for Lima and Callao, is now rehabilitating amunas in Huarochirí. At Quilcamachay-Vicas (Santa Eulalia sub-basin) it reports 8.25 km rehabilitated with about 1.43 million m³ per year of potential infiltration, with Coca-Cola Foundation funding and community involvement in operation and maintenance. These are potential-infiltration figures; the project page describes no monitoring indicators, so realised dry-season gains remain to be measured.

Read the full analysis: https://cris.pucp.edu.pe/es/publications/potential-contributions-of-pre-inca-infiltration-infrastructure-t/