Wow, I looked it up. I guesstimated it would have a cylinder diameter of 160m and depth of 20m and I was pretty close at ~22m x ~190m given (its an irregular po

Wow, I looked it up. I guesstimated it would have a cylinder diameter of 160m and depth of 20m and I was pretty close at ~22m x ~190m given (its an irregular polyhedron). Its an underground lake. I guess its a question of scale, I was referring to small rivers that meander through city suburbs and are part of the stormwater network and may have a few overflows on occasion, rather than a city of Madrid which has a population about 60% of my entire country. In New Zealand stormwater to my knowledge is not treated. If anyone else is interested: https://www.canaldeisabelsegunda.es/en/-/tanques-de-tormentas-protectores-de-los-rios https://www.canaldeisabelsegunda.es/en/-/tanques-de-tormenta...