Friday, December 22, 2023

Machu Picchu Water Management

 The ancient city of Machu Picchu uses a water source of natural springs that are located on the north slope of the mountain of Machu Picchu . The ancient Incan engineers created a very sophisticated collection system to carry the spring water to the city.


What is incredible is that the system remains functional to this day. A canal carries the water from the first spring to the city center

The canal is 749 m long, varying in width between 10 and 12 cm and depth between 10 and 16 cm, and stone lined. A cross section of the canal can be seen below in The average slope of the canal is about 3 percent  and gravity flow is relied upon for delivering the water to the city.

The design capacity of the canal to be 300 L/min while the typical yield from the primary spring is 25 to 150 L/min The ancient Incan engineers planned the canal well to be able to accommodate varying flow rates over time. The canal first enters the city in the agricultural sector and then into the urban center where it starts flowing through the system of fountains. The canal has a fairly steady slope on its way into the city.

The water from the canal empties into a system of 16 fountains throughout the city. The first fountain, fountain 1, is at the Inca ruler’s residence . This would have been the first part of the city planned out after the spring water source was discovered, with the rest of the city developing around it. 

Fountain 1 gives the Inca ruler the first access to the city’s water supply. Fountain 3 can be bypassed using a buried channel that carries water from fountain 2 to fountain 4. Starting at fountain 4 the water flows in series all the way to fountain 16 and then discharged. The 16 fountains are known as the stairway of fountains based on their layout . A map of the city with the spring, canal, and fountains can be seen below. 

Not only do the 16 fountains provide domestic water to Machu Picchu, but they also provide an aesthetic enhancement to the city with the sight and sound of the flowing water. The total vertical drop from fountain 1 to fountain 16 is 26 meters, and all the fountains besides the last one are easily accessible with common stairways and walkways. Each of the 16 fountains have the same general design and function. 

There is a stone channel at the top and a sharp spout edge that creates a water jet for easy filling of an aryballo, an ancient water jug used by the Incans.

The water fills at the bottom of the fountain and flows to the next fountain through a small circular drain. If the Incans at Machu Picchu experienced a dry period from their spring water source, they could use the Urubamba River as a secondary water source.

The infrastructure of Machu Picchu was designed to maintain the purity of the domestic water supply by directing the agricultural and urban stormwater discharges away from the domestic water canal. Drainage of excess water was crucial at Machu Picchu due to the location of the city. 

There is a threat of mudslides due to excess or extreme rainfall events. The agricultural terraces are one of the most recognizable and visual characteristics of the ancient city. These terraces not only maximize the available land for farming, but they help to protect against erosion. The subsurface of the terraces reveals a very well-planned drainage system with stones at the bottom, then gravel, sandy material, and finally the topsoil. 

The above schematics shows a basic schematic of the terrace layers. This layering effect provides strength for the terraces and ensures that water drains at an appropriate rate. The agricultural terraces are also sloped slightly which will direct the runoff into drainage channels that lead to a main drain that carries the water out of the city safely. 

The city incorporated many drainage holes into the walls and structures of the city, and many drainage channels into stairways, walkways, and buildings that carry runoff to the main drain. 

The Incans also built channels that collected water from the roofs of their buildings to be able to protect the building foundations and structures. Two collecting locations for excess spilling water are located above urban sector to keep runoff out of the main domestic water source. 

The very extensive drainage system at Machu Picchu is one of the reasons why the ancient city is still in very good condition and works to this day. The Incans built the city for longevity and it definitely shows.

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