Rain gardens are extremely common where I live. I think most cities require them for new housing complex or road planning over the last 30 years. They work a treat for slowing water flow, helping storm drains, and storing the water in the soil to help plants grow in the summer drought (and reduce wildfire risk near houses)
Here's a gateway to some of the plans that work well in our climate.
https://www.crd.ca/environment/stormwater-watersheds-harbours/stormwater/managing-your-rainwater
I'm always surprised they aren't more common elsewhere.
