If you're talking about a larger piece of land, and not just a garden, then swales would probably cause problems,
simply because most of the moisture would end up turning the valleys into mud pits.
That's where the P.A. Yeomans' Keyline design system comes into play, which you can read about here:
http://www.soilandhealth.org/01aglibrary/010125yeomans/010125toc.html If that's too complicated, I'm sure Darren Doherty would explain it to you at one of his workshops

.