I think maybe I didn't explain well:
I dug a hole for a
pond a few years ago, but it doesn't hold water long
enough to be a pond, so I started piling organic stuff in the bottom, burning wood scraps,etc. in there,
and now there is a nice layer of grass and organic material in the bottom. The bottom is always moist, even after weeks without rain.
One of the main points of hugelkultur is to store water in the rotten wood below the mound, my idea is pretty much exactly the same, except it is not only storing water that falls on the surface area of the mound, but also the water that is collected from the sloped sides.
A hugel with a rain concentrator basically.
This might not be useful for those in say, the Pacific North West, but here in Georgia we've had a run of years where we get tons of rain for a while, then weeks to months with little rain.