Contour lines, though it looks more like terracing
Still, you now have an idea of what parts of the colony are likely to get inundated when the Silverbough floods in spring, so any building there is going to be built "Queenslander" style on pylons (originally wood, probably later reinforced with mine tailings).
Also, the "boat houses" where in the ferries are birthed/loaded and the ends of their chain are anchored. As a note, having the chain under tension is decidedly odd, as the average chain ferry usually has a slack chain for reasons including allowing water craft to move past it. Keeping it under any sort of tension suggests that preventing continues travel south then west along the Silverbough might have been part of the colony's mandate. Given the width of the river, I picture there being a semiphore tower of some description on both sides to allow the ferrymen to communicate with each other -- possibly suggesting they hold a monopoly on "instantaneous" cross-river communications. Further, there might even be a Ferry Guild who control the right to raft the ore down river.
Of the various ways the ferry can work, I see the chain being strung between two spindles and passing through a mount on each ferry platform. Depending on whether that platform is being used, the ferry is fixed to the chain by bolts through the links. One team winds the chain onto their spindle, dragging the ferry(s) to their side of the river while a second team unwinds theirs. Thus you have 1st and last loads of the day being small payloads as one of the ferries is pulled to the other, with every other transit being both platforms hooked together. In addition to the ferrymen being burly hardcore guys, you could also argue the fact that the town's economy would be shagged without them gives them a degree of social status that isn't just due to them being able to crush your skull