Swale paradox: My observations

So I put in alot of swales. About forty plus over ten acres and placed 30 feet from eachother. I put half in this year over the summer and half last summer. This year I noticed a definite difference between the new swales and the old swales. The new swales put in this year, gathering substantially more water than swales from last year despite being in areas that theoretically should get less runoff. So my new trees and cover crop performed far better in the fresh and raw swales. In the old swales, the trees are struggling and dying off.

My only working explanation is that the old swales allowed more grass to grow and this absorbed water instead of allowing the water to run into the swale. Less water reaching the swale means the trees are getting less water hence their inferior performance. Secondly, increased herbaceous growth in the swales is now competing with the trees when they had a clean slate last year. Has anyone else observed this effect? And, is there anything to be done?

I will also share a victory, my property had WAY more fruiting prickly pear than the surrounding properties. I fill multiple five gallon buckets and left half of the fruits for the wild life. Within 100 feet of my property, the prickly pear fruit rate dropped off to zero. So the swales must be infiltrating more water and even percolating it some distance into the surroundings - even slightly uphill.

From; /swales_killed_my_trees_

"So it’s time we talk about swale fails.
The biggest one I’ve seen and discussed with a lot of experienced designers in the movement is where swales are just too deep for the site specifics.
A lot of this may be caused by seeing those massive swales Geoff Lawton builds in Australia.
Those swales have a function in Australia, on Geoff’s massive landscapes, on soils that are hydrophobic, and with infrequent, huge precipitation events.
But elsewhere in the world, swales that are too deep destroy the landscape hydrology, make the soil dry, and kill our trees and crops."

Thank you, John. That post was gold and I had never seen it before. So the old swales are working, just infiltrating more. And as the deep swales get filled in with sediment, their performance should improve.