@tsarstepan,
That area has flooded over and over for years, don't know if it is still doing it.
Cottonwoods and Willows have questionable business being there.
Western cottonwood is a california native but it is problematic with its greedy roots and its water need, though it's true it is a basin area; they sucker with root disturbance. They get many pests. They don't do all that well where winters aren't cold, and they really aren't in that place. So that's a maybe to me, with a frown. Willows, no, to me. Shallow invasive roots again, need regular to ample water (ample in the valley, I've no doubt, and the area doesn't naturally get a lot of water a year). If there is a california native one, it's not in my source books. They are weak wooded and short lived, subject to a lot of pests.
Lots of improper tree choices were made in the eighties; although these may be defensible, maybe there are smarter choices.
The Army Corps of Engineers has famously made lots of errors in the past, but they very well might know what they are doing in this Sepulveda Basin situation. Among other things, they may be redoing it for better long term site health, including that of wildlife.
I have a couple of landscape architecture colleagues that I would listen to on this, so I'll email them re their opinions. They both know the shaping of the basin better than I do, and the current planting. (I been by the basin but never walked it.)
