Chihese Hakka House Idea for Garden: How to Protect Soil in Raised Bed in Heavy Rains

I live in Fujian Province, China. The climate is sub-tropical monsoon. I want to build a 3 meter diameter raised bed. Originally, I was planning to build a geodesic dome greenhouse, but I think the summers are too hot for this.

Instead, I want to build a 6 meter diameter earthbag round wall (3 meters high) around the garden for wind protection and privacy. The style would be similar to the Chinese Hakka houses. I don't want to build an enclosed roof, only a roof to cover the walls and 1.5 meters inside the garden round house.

See picture of round hakka houses here https://en.wikipedia.org/wiki/Hakka_walled_village

I also got inspiration from the Forestier Underground Gardens http://www.undergroundgardens.com/


My question is, how can I protect the plants and soil from the heavy rains which occur during rainy season?


Dustin