I would look into native plants and shrubs. Possibly native flame azaleas. Not sure of others but try searching online. I think a place called Niche gardens. And please, if you don't already have it, carry flood insurance. I cannot stress this enough.

Absolutely native plants would be the best in such a natural environment. A naturally occurring riverside shrub is Virginia sweetspire - Itea virginia. There are low growing forms if you think height is an issue: 'Little Henry' is one. This plant suckers a bit in ideal conditions so it would help with erosion. It is not evergreen.

Native evergreen plants that you could mix in would include Mountain Laurel (Kalmia latifolia) and Inkberry (Ilex glabra).

All of these would thrive in those wet, part shade conditions. You can easily get these plants at better nurseries like Buck Jones in Woodstock/Roswell or Grayson.