Machu Picchu Can Handle the Rain

The marvel of Machu Picchu is in its infrastructure and that it was built to endure, according to Denver hydrologist Kenneth Wright. His wife, Ruth, adds, “The seven hundred terraces at Machu Picchu were designed to absorb and control rainfall and to stabilize the steep hillsides.”

The two Wrights have studied Inca civil engineering at Machu Picchu for the past 15 years and have published extensively on this World Heritage Site. For their scientific research at Machu Picchu, the couple has been awarded six academic degrees from Peru universities, along with individual decorations from President Alan Garcia in 2007.

The recent deluge in Peru was not unusual for the 500-year-old archaeological site. Engineer Wright pointed out that the Inca civil engineers designed Machu Picchu for longevity. This included a drainage system that would work under nearly any rainfall that could occur. The skill and foresight of Inca engineers are what made the site the masterpiece it is.

The Wrights added that the Inca provided subsurface drains under the central plaza using hundreds of thousands of white granite stone chips to support the plaza, but also to safely carry off any excess water. (The chips were the leftovers from cutting the granite building stones.) It was under the plaza that the first and only gold was found at Machu Picchu in 1996 by archaeologist Srta. Elva Torres, who excavated in this location for the Wrights’ soil samples. Throughout Machu Picchu, 50 to 60 percent of the ancient work was underground, in the form of site preparation and foundations, the Wrights estimate.

The hundreds of terraces that stabilize the steep slopes of Machu Picchu were built with great care with what the Wrights call “inverse filters.” These filters are permeable and efficiently handle percolating water. The water that does not percolate downward into the filter runs off via elaborate surface drains to the Main Drain (popularly known as the “Dry Moat”).

During their research, the Wrights counted about 130 runoff drain holes to handle rainfall runoff that the Inca incorporated into their masterfully built walls. An example that Ken Wright likes to point to is the drainage outlet under the Inca Trail, not far from the guardhouse. The culvert is in perfect condition after 500 years of operation. Wright takes colleagues to this culvert and explains that the Inca designed with a high standard of care.

“Modern engineers can learn a lot from the ancient Inca civil engineer.” Ruth adds.
Machu Picchu was built as a royal estate for Inca Pachacuti between AD 1450 and 1534. It was meant to last forever. The Wrights have gone on about 20 expeditions there over the years and have found that the Inca were good engineers. They feel Machu Picchu is a civil engineering marvel of which all can be proud. They are planning another research trip to Machu Picchu to document how well the archaeological ruins have withstood the recent rainfalls.

Photo Captions



Ruth and Ken Wright have studied the hydrology of Machu Picchu since 1994.



The Main Drain divides the agricultural and urban areas of Machu Picchu.



The well-drained and constructed terraces of Machu Picchu are the secret to slope stability and erosion control.



Rock chips from stone shaping were used at Machu Picchu for subsurface drainage.



In the excavation shown in Photo 4, this gold bracelet was found. It is the only gold artifact found at Machu Picchu.

16/feb/2009