I originally didn't want to sandbag because of wanting to keep plastic out of the soil, but it looks like it will be absolutely necessary in a few areas. Considering the amount of trash and plastic we've pulled out of the soil since moving in, I guess we have good enough karma to add a bit back in the form of sandbags. If we could get some bamboo to break through the sandbags and root, we could eventually reclaim those areas.
After seeing how fast the river moves when flooding, especially through a particularly narrow section on our property, I think tent platforms will be the most reasonable things to put near the river. Four legs and no walls or roof, and something hydrodynamic on the upstream side like a water deflector, or perhaps a torpedo-shaped tent platform 🤔.
We just got a few new varieties of bamboo for planting, one that doesn't spread aggressively and has tasty shoots, and another that grows slowly but makes nice and straight tubes good for furniture. There is also lots of local bamboo growing in the forest, will probably supplement with some of those too.