Source: Translated and adapted from: "MACHU PICCHU: A CIVIL ENGINEERING MARVEL". Published in: CIVIL ENGINEERING MAGAZINE. January 2001

When the American hydraulic engineer Ken Wright saw some Machu Picchu photographs, taken by his wife during a visit to Peru in 1974, and heard her comments about the pools and other structures built by the Incas for water supply, he was motivated to visit the famous pre-Columbian ruins and started on-site research on the topic.

Yet, twenty years passed before the Peruvian government consented to research in Machu Picchu. Since 1994 and for the following six years, together with his team, Wright visited the place from one to three times each year while working full time for his own company, WRIGHT WATER ENGINEERS.

During the years of work in Peru, Wright collaborated closely with Alfredo Valencia Zegarra, a Peruvian archaeologist who devoted an extensive part of his professional career to studying Machu Picchu. In the year 2000 they both published the book Machu Picchu: A Civil Engineering Marvel, from which some of the following paragraphs have been taken.

"The city of Machu Picchu, once the royal state of the powerful Inca Empire, lay hidden in Peruvian mountains until 1911, when Hiram Bingham, Professor of History at Yale University, discovered its ruins. From then onwards, it has become South America's most important archaeological site.

In 1450 the Incas reached this place, a 2,440 meter-high ridge in the Andes range, with a goal in mind: to build a state for their emperor Pachacutec. They had "the perfect site", Wright notes, but one whose suitability must have been only obvious to an experienced engineer. The slopes were very steep and sheer. How could the buildings be prevented from sliding downhill in the middle of heavy rains? How would drinking water be made accessible? And from what source would the water come?"

Wright's research obviously revealed that they must have carefully planned the city before building it. First, engineers had to determine the spring's exact location and whether it would supply the population's needs beforehand. Wright's team found that the fountain, on the steep slope of a mountain to the north of Machu Picchu, is fed by a 16.3-hectare tributary drainage basin. After conducting an inflow-outflow evaluation, the team also concluded that the spring draws on drainage from a much larger hydro-geologic basin.

The Incas enhanced the spring's yield by building a spring collection system on the hillside. The system consists of a stone wall about 14.6 meters long and up to 1.4 meters high. Water from the spring seeps through the wall into a rectangular stone trench about 0.8 meters wide. Water from a secondary spring enters the channel about 80 meters west of the primary spring. The Inca also built a 1.5 to 2.0 meter-wide terrace to allow easy access for operating and maintenance work. The spring's condition surprised Wright. "The spring works were still intact, still working and yielding water after all these centuries of abandonment."

However, before the city could be built, Inca engineers had to plan how to channel the water from the spring, at an altitude of 2,458 meters, to the proposed site. They decided to build a 749 meter-long channel with a nearly 3 percent gradient. Inside the city walls, the water would be made accessible through a series of 16 fountains, the first of which would be reserved for the emperor. This is how the channel design, says Wright, determined the location of the emperor's residence and the layout or planning of the entire city of Machu Picchu.