“Canals are made of flat water, and flat water is difficult stuff to get hold of. It is expensive. You use locks to keep it flat when you go up hills. Sometimes, you have to take the water under hills in tunnels in order to preserve its flatness. Canals were not cheap to build.” WaterLocksCanalsWaterwaysCanal LocksFlat WaterWaterway Engineering Book:Parallel Lines: Or, Journeys on the Railway of Dreams Source: Parallel Lines: Or, Journeys on the Railway of Dreams