So rather than have sewer pipes throughout the city, why not demonstrate that this is a proper Imperial town, and the North-most Imperial Town at that? GIve it something really iconic that separates it from the other towns. Aqueducts sprung to mind, bringing water from the nearby mountains, with enough of an elevation on the duct to prevent freezing(though it doesn't look like solitude has an issue with snow) These could be decorated with statues of Emperors or Divines(of course taking into account politics, removing statues of figures not allowed, maybe Talos or an Emperor in the event the Stormcloaks take the town).
This Aqueduct could also be used for an above street level causeway for a Thief or Assassin looking for a sniping point during a specific event. (get what I'm getting at?)
Now you might say that this can't be done now that the game has been released. Mods could fix that. I throw this idea out for any modder or people who just like the idea.