<Li> weirs and dams to raise river water levels to usable depths; </Li> <Li> looping descents to create a longer and gentler channel around a stretch of rapids or falls; </Li> <Li> locks to allow ships and barges to ascend / descend . </Li> <P> Since they cut across drainage divides, canals are more difficult to construct and often need additional improvements, like viaducts and aqueducts to bridge waters over streams and roads, and ways to keep water in the channel . </P>

Where does the water in canals come from