Sitting above and to the right of Cercedilla is the Navalmedio dam and its reservoir which I first heard about from the previous owners of our cabin while we were finalizing the purchase. They said it was a nice walk from the cabin, and I was quite confused thinking they were talking about the Navacerrada reservoir which is quite far away. So early excursions from the cabin centered on exploring and finding the reservoir. Read on for what I have learned about it!

Data points about the dam

• Construction was completed on 31 December 1968 (unable to find any information on how long it took to build)
• Designed by an engineer named J. Gavala who also did the Navacerrada dam at the same time
• 47 meters tall (155 feet) (about a 14 story building)
• 170 meters long (557 feet) (1.5 football fields)
• Reservoir has around 8 hectares surface area and a capacity of 1 cubic hectometer (around 400 olympic swimming pools)
  • Its main use is to transfer water to the larger Navacerrada reservoir
• Location:
• Great loop walk where you can get really close
• It is a gravity dam:
  • Holds back water purely through its own mass: The enormous weight of the structure — pressing down onto the foundation — creates enough friction and resistance to counteract the horizontal push of the reservoir behind it. No cables, no arches, no external anchoring. Just mass.
• Drawings from Iagua:
  
• The dam is classified as Category A for potential risk — the highest risk category in Spain, meaning a failure would have serious consequences for populated areas downstream. I think these speakers are what would warn us if a failure was imminent:

Pictures

Fall Day:

Downstream face:

Upstream face

Mirror lake:

Sluice gates:

Downstream face with wild Paeonia broteri:

Links, References and things that helped with this

• Canal de Isabell II’s data sheet about the dam
• Iagua’s data sheet about the dam

Thanks for reading and feel free to give feedback or comments via email (andrew@jupiterstation.net).