Thanks Dan,
Swale systems such as you describe (if I am picturing correctly) can be and have been designed and accomplished... Yes, you can design a 'spillway' at either end of a swale (and all swales generally
should have spillways anyway), or you could actually put the spillway anywhere else along the swale as well... wherever some extra
water will fulfill the most functions or address your goals best.
A question you might want to consider on the pasture area you describe is whether or not you need an entire series of interconnected swales at all... ? This will depend on what your goals are for the land. If your goals include a large hugelswale at the base of the slope for growing a diverse yielding
polyculture, along with generally harvesting all the rainwater you can, and having healthy pasture above the hugelswale, then perhaps you don't need all the other swales... and could save the expense/time/energy of building them. Instead of harvesting water along relatively thin strips in the landscape, every so often, you could manage the pasture to be a 'sponge' over its entire surface area (not just thin linear strips), then catch anything else in the very bottom swale
hugel... Managing for an effective water cycle--creating a sponge--on all of the land will store more water more evenly across the pasture, and can be accomplished by holistic planned grazing, by keyline sub-soiling on keyline pattern cultivation, or many other strategies which can be integrated to generate what I sometimes call an 'amplified topsoil explosion'! We will cover these in some detail in the Colorado
workshop, July 22-24... hope we see you there!