Originally Posted by kuroba

I have no idea if they have a particular name in English but those are pools to contain and redirect landslides. Where I live it's a desert terrain but sometimes (every 10 years or so) we get an unusual amount of precipitation which back in 1991 caused a series of landslides that severely affected the city. The pools were built a few years later in the major ravines around the city to prevent this from happening again.