I too live in the PNW and have been managing to much water on saturated soil
I've found that you have to be careful in your swale design - to deep in spots and the water slows (relatively speaking) and then soaks in down hill and turns that area into a mud bog....with surface water. Uneven swale bottom can have this effect too, or to little of a grade. You really have to watch how the water moves in your ditches/swales.
I had to redesign my
pond run off ditches last week during heavy rains. My animals had messed up last years work. I created steep sides and smooth grade transitions with small (inches) waterfall drop offs every now and then. This sped up the water flow through the ditch on contour, and the land down hill dried - that is to say it was no wetter than any other place under that much rain. Surface water had disappeared. Before my ditch the water spread out, running all over the surface of the land. This leaches the land of nutrients. So personally I would not capture and/or slow down water where buildings, roads or animal housing was just down hill. My garden is just down hill of my pond's overflow. There's a time when we want to slow down and even capture water, but there is another time when draining off water from certain areas is a necessity. A plan for draining water is a good thing for the land when the water is obviously doing damage.
I plan on running extra winter rain run off quickly to my seasonal creek, where I will be putting in logs and rocks every so often to build mini dams to slow the water in the creek. The creek has very high sides so water expansion will not be a problem in the that area.
My neighbor put in a very small pond on the high ground just above his RV and outbuildings last year. This year, he was complaining about all the mud and water even with lots of rock being dumped. I asked him if he had sealed the down hill side of that pond and he said no. I said he was the one who was bringing in more water to his compound. And the next day he was digging a french drain in front of that pond. He has since reported things are back to normal (for Oregon) in his living area. He ran his french drain into his seasonal creek. With french drains you do not have as much issue with the downhill grade of the ditch as you do with a swale. The pipe helps to 'move' the water.
