I've always wanted to have a nice harbor in my base where I could put the boats and maybe dry some fish right by the side of the water but it's impossible to secure an area that has a water edge. It's certainly not a necessity right now when boats aren't even good for logistics, but if we ever get bigger boats that don't come out of the water (and if they are you know actually useful because the river system is contiguous), then a secure harbor would be essential.
To secure a harbor I propose the use of a chain like that which was famously used as WestPoint, it would span across a variable sized length of water, the chain effectively functions as a gate and is built like any gate by first having two corner posts in line with each other, but rather then a set size of 2 the gap can be up to ~30 tiles of only shallow water. The chains material cost is proportional to length and I'm guessing 3-4 Iron bars would be appropriate per tile. The chain can then be locked and keyed like any gate and the chain graphic sinks into the water to indicate it is open and rises just above the water to indicate closed.
The existing wall posts would naturally be used and iron chains could pair with the upcoming 'brick' wall we have been teased with, the soon to be second tier plank wall could pair with a cable of rope that uses several ropes per tile, perhaps with some glue or other expensive materials too. Generally I think the water barrier should be equal in strength to the walls normal gate segment but more expensive to build.