Situated above the Urubamba Valley and Urubamba River in Peru is a 15th century Inca site called Machu Picchu, and it is one of the most familiar and visited sites of the Inca. While the exact reasoning for its construction and its later abandonment are still being debated, the site remains an incredible marvel of engineering and planning. The design and implementation of water system and drainage in the city show an incredible amount of sophistication and have been instrumental in preserving Machu Picchu for over four centuries.
The city is continuously supplied with fresh water via a spring higher up the mountainside A spring collection system was constructed to gather the water from the spring. From there, a gravity-fed water canal takes the water over 700 meters from the site of the spring to Machu Picchu and provided fresh drinking water to all of the inhabitants of the city, which may have ranged between 300-1000.
The canal feeds runs through into the city, first through the agricultural areas and then the urban area where it supplies 16 fountains that provided fresh water for the inhabitants. The fountains were designed to accommodate a range of flows from 10 L/min all the way to a maximum of 100 L/min while the channel is designed to accommodate nearly 300 L/min. The reasoning for this was because the yield of the spring was dependent on rainfall and an excess amount of rainfall would send more water through the canal but the fountains didn’t need to provide that much water for the people. To deal with this, the canal has two control points along its length inside the city in order to make sure that water never exceeded the amount that the fountains could provide which could have damaged the system. The excess water would either go into the agricultural area or through the main drain before it reached the fountains.
Agricultural drainage at Machu Picchu
Drainage at Machu Picchu presented a problem because of the steep slopes which the city rests near. This area had the potential for landslides due to the slope and the amount of rainfall and could have damaged the city. To combat this problem, the Inca placed agricultural terraces along the slope. This decision not only created land for farming along an otherwise unusable slop but it also stopped erosion because of the subsurface drainage that was constructed.
Below the top soil layer of each terrace is a layer of sand, followed by a layer of gravel, and then a layer of loose stone at the bottom. This allowed for proper drainage of the terraces and the top of the terraces were even sloped towards surface drainage systems to remove excess surface water. This design ensured that the terraces would be stable and not affected by the rainfall that the area experiences
Urban drainage at Machu Picchu
In the urban area of the city, drainage was also very important. The thatched roofs of the buildings increased the runoff from rainfall events and the water needed to be removed from the urban area as so much of it was not able to infiltrate into the ground. To deal with this, drainage features were integrated into most structures. Walkways, stairways, and the interiors of buildings all featured drainage channels to collect the water and move it towards the main drain of the city. From the main drain, the water would leave the city and go to the valley and river below. The large plazas of the urban area were also constructed similarly to the agricultural terraces in terms of the subsurface materials and drainage.
The water and drainage systems of Machu Picchu show an amazing amount of knowledge and engineering design on the part of the Inca people. The systems were not added as an afterthought but planned and designed before or during construction. Since their creation, the drainage and water systems of the city are still performing as they were intended to and preserving the Machu Picchu despite it being abandoned over 400 years ago.