I think miscanthus varieties will do well by the banks of the river.
Not to mention all the rushes (juncus), sedges (carex) and like species that grow in, and close to water or boggy areas.
I would think you can have lots of fun with this project.
Not a grass, but check if Gunnera will grow in your area. It is a fun, big plant and likes to be wet. Might be too cold in Jersey though.

You might want to try blue eyed grass which is actually a member of the iris family but very pretty.

Shorter grasses that like it wet include Chasmanthium latifolium (Northern Sea Oats) and Deschampsia caespitosa (Tufted Hair Grass).

Might be a good spot for one of the shorter bamboos.