There is a spot in my front side yard (near the road and the drainage and water pipes), which holds a large pool of water for days or weeks during periods of heavy rains. I need to plant a tree here, but I don't want it to invade the pipes. Thank you for your list of wet soil trees on this website! Can you suggest some trees with non-invasive roots?
What Wet Soil Trees Will NOT Put Roots Into Water Pipes?
Certified GKH Gardening Expert
Magnolias normally can handle wet feet, but with being newly planted, yes, it could be the shock that is causing the leaves to drop and the excess rain could be making the shock worse.
I would look into a temporary solution as for getting the water as once the trees are established, they will like the extra water on occasion. Normally, for some one in your situation, I would recommend building a french drain, but it sounds like that it already along the lines of what you have done. This article may also help: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/yard-drainage-problems.htm