Advice needed for difficult area of the garden

Also whilst you're all here.....
I have a border between ours and our neighbours property. She has given me the go ahead to plant the border up but it floods very easily.

There are some daffs coming up, and we had a viola hybrid border last summer, but id like something permenant, something hedge forming that can withstand very wet conditions. Low growing preferable (no higher than 2ft but I can prune etc)

Thank you x

Is it always damp or it is wet because of the recent weather conditions? 2 perennials that I like for wet places are astilbe and rodgersia. There is a shrub called Clethra which likes it wet

 

but it is 3 - 4 feet, but I think there are dwarfer ones. One disadvantage is that it's leaves are late to come out in spring, but it is pretty in flower.

Its whenever we have rain it floods so it resembles a moat. I'll look into the dwarfs of that one thanks