What can I do with a backyard that floods?

I have close to an acre backyard which I would love to make usable unfortunately, it floods approximately twice a year. I have spent over $6,500 for fill dirt and ditch drainage on each side of the property. I even had the creek, which runs between the yard and the hillside of trees in the background, dug deeper and wider but that too was a waste of money. After the fill dirt job the ground was bare. I sowed it with mixture of fesue grass seeds which is recommended for the area I live in and covered it with straw. However, the crab grass won out. The ground beneath the crab grass and dandelions is hard and infertile soil even though I have been generous with fertilize and topsoil. Although the flood water doesn't get very deep it is swift and has washed away flowers, shrubs, young trees and yard ornaments. The only tree I have left is in the pic at the edge of the yard. A willow that isn't doing all that well. The water has never gotten in my home, for which I am thankful, but it does get near the back deck where only a small group of Primrose has survived. So I'm reaching out for any ideals for helping to make my yard look more attractive.
q what can i do with a backyard that floods
A view of my backyard
q what can i do with a backyard that floods
Flood water at the edge of back deck
q what can i do with a backyard that floods
Primrose, still surviving
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