wrote in message
ups.com...
What stops a pond from overflowing, and water spilling out into the
garden, when there is heavy rain?


If you're talking about an existing pond ... not a lot, unless you redesign
parts of it to incorporate an overflow system (covering the overflow with a
gauze so fish don't get stuck). I wonder if there's any eleectrical system
that can detect the level of water rising and pump out water until it
returns to level.

I guess that the design and working of a filter system may provide a
solution for some sort of overflow.