It is filled to the brim with sand, however, and through the sand is an underflow.
From the area of water-bearing gravels found, it was proposed to tap the underflow water at the 630-m.
The general scheme for tapping this underflow was to drive a main gallery at the 560-m.
The water is almost wholly taken from the rivers, but underflow is also utilized, especially in San Luis Park.
Here the waters lost themselves for many feet in the underflow so common in this land of aimless, uncertain waterways.