Hi Krystle,
Your assumptions are correct. Riverbanks, flood plains and wetlands would have favorable conditions for weeds to thrive in. As all of these waterways may be potentially inaccessible during the wet season they could all be locations where weed management is difficult.
This article mentions weed management strategies which may be useful for your research: Life on the land with the Lama Lama rangers – a picture essay
Kind regards,
Evelyn