You know, you're right. Eventually that irrigation won't be needed. But I'm on flat land so swales are not as effective as on a slope. The irrigation is to establish a cover crop. I'll explain in more detail in a future post so if you're into this kind of thing, follow me and watch for it.
You make a very good point and it deserves its own post as a response. When I post it, I'll add a link back to it from this reply.