Building on my previous thread and taking into account suggestions Long distance travel by non-motorised rolling vehicles
I wish to consider two-way rivers that flow in opposite directions at the same time.
There is a high fertile plateau surrounded by flat scrubland. Rain is plentiful on top of the plateau and waterfalls occur around its edges. At the moment, these falls create rivers that flow away from the plateau in various directions, ending at the sea. This is great for transport by boat when exporting crops from the plateau, however it is hard work going upriver when the boats are bringing imports to the plateau.
The proposed system
A trial is to be performed with the biggest of the rivers. It will flow to the sea as usual but, before it gets there, it will be sent on a long diversion. Canals are to be built that carry the river to outlying cities and back.
Boats do not need to be powered, they all travel with the flow of the river.
I know about canals that currently exist on Earth but as far as I know, the flow is prevented by locks and any flow is one-directional. Has anyone used this proposed system before? If so where and when. If not why not?