As an alternative to plummer's hemp after a visit to my sister's allotment, I came across some asparagus plant tops. Reeds -bingo! OK, a bit of colour correction needed, no problem. They dried easily and are pretty flexible, though a splash of PVA in the yet to be airbrushed on colour adjustment won't do any harm. The rhyne bed will be repainted and recoated in PVA in due course though the paint splashes do look a little like stuff you seen in stagment canals etc.