"Include canals" does not seem to distinguish between canals that have replaced natural drainage channels, and those that connect different watersheds - which m

"Include canals" does not seem to distinguish between canals that have replaced natural drainage channels, and those that connect different watersheds - which may or may not be what you want. This is noticeable, for example, in the English midlands, where the major watersheds merge into one connected entity (maybe because of the network of pre-railroad navigation canals?)