But, I can't see any reason that he couldn't do so by himself, at least in limited quantities, aside from lack of idea or lack of tradition of doing so.
We already know the physics of Erfworld are slightly different [Lava lake that never cools], so this will mainly be Pure Speculation mixed with a small touch of what we have seen happen so far.
We know that Sizemore is able to create tunnels in a hex that is not a city [Its what he just did in The Magic Kingdom]. Not much difference between a tunnel and a ditch, or say an aqueduct. Assuming that Water, Lava or a liquid in general (who knows if there are Acid lake terrain types yet) flows to encompass its container, and as we have seen no reason yet that Dirtamancy cannot Eventually (with a lot of Juice) cause an entire hex to be shaped into a ditch/aqueduct/valley that is incredibly deep, well it would be like irrigation on a large scale. He could change the terrain of a hex from a plains, forest, mountain, etc, into a river [of water or lava]. Something like that would severely aide a side thats heavy Navy and Air because then you don't have to worry about ground types as much, since without a bridge you can't really get ground types across that terrain. Its like making a moat
Course then the question becomes, does an artificial terrain provide the same benefits/penalties as a "natural" terrain, and would it persist as long.









