The Ark Class ship formed part of the three-fold survival plan of the wealthy and powerful of the Petroleum Age. The other two legs of the plan were the arcologies, and space habitats.
In a small farming community, the only way to cross a river is to basically pole vault across. A small section of river has a small raft on a string to pull items across but for a person to cross they must use one of the many provided poles. Might be interesting seeing what the players do when they come across it. Villagers do it all the time so are skilled and can do it with ease.