I'd imagine that since, for some reason, the river is in heavy use, that cranes would be somewhat abundant. Heavy lift capacity cranes, such as those that could be constructed over natural or unnatural holes even more so. I would think that your water enterprise would surely have cranes of significant capacity Redrobes. No doubt it would actually be more efficient to lift product down to boats for farther flung areas of the city (I think these city roads would have extremely heavy traffic issues).