After pulling up all the previous ground cover -- clover, and liming the soil, we had several weeks of torrential rain. I feel confident in saying that all the lime got completely washed away, along with a good deal of topsoil. When the clover was in place, the soil was never washed away. But ironically, the heaviest rain I've ever seen, anywhere, fell just after we pulled up the ground cover.
The soil did a pitiful imitation of the Mississippi River, carrying our topsoil off to the sea.
The next lot of ground cover that we decided on is a sort called Lippia nodiflora (iwadare-kusa in Japanese) which is said to grow like billy-ho, and be reasonably resistant to drought. I really hope it is, because I'm not in the habit of watering 'lawn' space.
As a means of preventing the whole plot of land washing away completely, I carved out channels running across the slope, with the soil piled up on the downhill side. The Lippia is planted along the little berms.
This actually worked quite well for a few days more of the torrential rain, but without any well-established ground cover, the ditches and berms are beginning to get flattened.
The rainy season was officially declared over on Friday, when we had some typical summer weather. But then on Friday night and Saturday morning, we had a massive thunderstorm that shook the whole house, and on Saturday evening, we have the same son et lumière again, with more Biblical quantities of rain.
I never thought that the anxieties I'd face in life would include the loss of my precious topsoil. More rain forecast for tomorrow...