You can still gather runoff by putting in something like farm tile and direct drainage into the pond basin, or just some simple ditches to do the same. Make sure the pond is designed to sit a little lower so water can run into it without it backing up into the drains when full.

The big question then becomes what is the soil like? If it drains well, it may never make it to the pond.

BTW an 8" drop though a dry summer is not a lot. Many of us have a ton of runoff, and poorly constructed dams loose more than that. Last summer during a drought I was down almost 3'. It wasn't pretty. This year I have had water running through it up until two weeks ago when it finally stopped pouring rain.