What perplexes me is that these earthen structures have not fallen into invisibility through erosion and become mere depressions that are hardly recognizable as man-made.
The other factor is being able to run a line of levels this far across terrain and get the right slope to encourage adequate flow without over flowing.
Parts of the original canal silted up. About 300-350 years ago there was a need to build a canal system in England to drain off standing water and open up more land for agriculture, which also transitioned into the pre-rail heavy cargo transit.