Yeah, i have seen some of the people doing rain gardening. Actually they have large plastic boxes and they used to store rain water in them. They use that water for the irrigation of their lawn and their lawn is very attractive and is growing day by day.
I have a few beds in front that I call a 'rain garden'. They are not for ornamentals, but for veggies. They receive the water from one downspout after the rain collection containers are full. The sunken beds don't become bogs because there is very good drainage.
The purpose of my rain gardens is to prevent any water that falls on the property from leaving it. We (SoCal) are still in a severe drought, and in spite of this last El Nino, we only got 60-70% of our annual rainfall.
5 years later.....
The two beds I used for my so-called rain garden in the front yard have more than filled with organic matter bringing their level from a few inches below surounding soil in pathways, to a few inches above it. They were not intentionlly filled, it just happened with additions of mulch and its decompostion. These beds have been no till since then and plants growing in them are doing extremely well. The soil in these beds is soft and rich.
I still divert rain into this front garden area, as well as in the back yard, when we get any. There has been zero problem with run-off. The land is very thirsty. Last year we got about 7 inches of rain, which is about half our average.
Coastal Southern California, zone 10, avocado belt, still in a drought.
Thanks for the update gianna. I remember watching something on HGTV years ago (when the G actually stood for garden) and was enchanted by a tour through a sunken garden. Of course it was mostly perennials but I can definitely see now how it would be advantageous to vegetables especially in a dry year.