I see what youre saying about a very shallow lake of water used as a leveling device, say only an inch deep or so .
In fact the entire course surface wouln't need to be covered in water.
Islands would form in the high spots which would remain dry allowing them to be worked upon, the work eventually reducing the dry islands down to the shallow water level.
A quantity of water could then be released further exposing the 'high spot' islands which are again dry worked down. The process is repeated over and over until eventually there are no large islands and of course no water. In other words a flatish surface consisting of numerous very small dry islands and small very shallow pools.
Imagine a parking lot after rainfall, small, very shallow puddles all over the place. Good enough???
Anyway this would negate the problem of working in dirty opaque water, and would ensure minimum material removal and therefore effort in order to achieve acceptable flatness. No measuring equipment or projection equipment required.
Obviously this would only work on a horizontal reasonably flat surface.
Actually I'm surprised that Lehner even considered level reduction work going on underwater.
Edited 1 time(s). Last edit at 15-Jan-17 02:12 by Jon Ellison.