In February of 2017, the Oroville Dam spillway in California was severely damaged due to heavy rain. The failure was attributed, in part, to the drainage system below the spillway. Water can create pressure that lifts and moves structures, so drains are used to relieve this pressure. French drains, named after American inventor Henry French, are commonly used for subsurface drainage. They consist of a perforated pipe surrounded by gravel to allow water flow while holding back soil particles. Properly filtered drains are crucial for dam structures, with many high-profile failures resulting from inadequate drainage. Sand is often used for effective filtration. Subscribe to Nebula for more independent, thoughtful content at a discount.
https://practical.engineering/blog/2024/8/6/how-french-drains-work