The old version with the river-bend.
The new version without the river-bend.
The river-bend was due to a piece of deduction, where the location of Shalebridge and it's relation with Newmarket, and Newmarket's relation within the Assassins! -map, and Old Quarter's relation with said map and T3 map defined it's location to be where it is. Check maps from T3 manual, the Assassins! and consider the conversation of the Bafford's servants from T1.
No known dev comments should exist, simply our work here.
Atleast in the old version I was thinking of the 'delta' as a set of canal-works that were dug to support the City's water-supplies, much like aqueducts (except that here they were dug into the ground, most likely because of the hillside the City is located in (check cutscenes and intros); perhaps to regulate the flow-speed and because it was cheaper to dig through a few hills, than draw a set of pipes all the way from the mountain atop them).
In the old map the canals would begin from the first turn downwards, explaining much of the canals seen in Sealed Section, Ambush! and Assassins! (+Pagan Sanctuary).
And yes, I prefer to think fantasy settings having *add-on* rules of magic, instead of changing any of the existing laws of nature. Otherwise where should we stop manipulating the logic, eh?