Paleohydrology of the Incamisana Watershed and Mountain Canal System at Ollantaytambo, Peru

The Incamisana, at Ollantaytambo Peru, is an ancient Inca water temple that exemplifies the high level of understanding the Inca engineers had for hydraulics and hydrology. The hydraulic engineering at this site extends up the mountainside in an extensive mountain canal system. The purpose of this study was to analyze the water supply to the Incamisana from a hydrologic point of view. The current sources for the Incamisana is the Rio Patacancha, and through field studies, a mountain stream has been identified as another potential source, via the Bandolista Canal, although the Inca may not have used it. There is no evidence that the Incamisana was fed by a spring source. There are consistencies in canal design; the canals typically have similar dimensions and 1 to 2% slope, which result in a subcritical flow, canals also had the ability to transport sediment. At 50% full, the canals had a capacity of about 5 million gal/day from the mountain streams, down to the valley where it was used. Fieldwork, flow calculations, and a watershed run-off analysis show that there is sustainable infrastructure and adequate water to supply the Incamisana, and also irrigate the agricultural terraces.