Ruth Delany, in her Ireland’s Royal Canal 1789–2009 (with Ian Bath) The Lilliput Press, Dublin 2010, tells us that the promoters of the Royal Canal decided to divert it through Kinnegad. In January 1801 the Directors General of Inland Navigation asked the engineer John Brownrigg to inspect the route:
Brownrigg was very critical of the diversion proposed in order to pass through Kinnegad, which he said would bring the line through bog and broken quarry. The route through Thomastown was not only better, he felt, but brought in a good water supply ….
John Rennie too, in 1802, criticised the Kinnegad route, even though work had begun on its construction — despite the fact that the company would have needed approval, which it did not get, for that diversion from the route originally approved. The Kinnegad route was abandoned, but the company owned the land for many years afterwards, which may explain why it was shown on the 6″ Ordnance Survey map of ~1840. Here is the western end of the work.
Here is the central section; my map extract overlaps slightly with the extracts showing the two ends.
Here is the eastern end, showing where the Thomastown route went.
Here is an overview of the route. I tried underlining it in red but my line is a bit wobbly.
You can follow the route for yourself; this link should take you to the place where the abandoned line diverges from the current line of the Royal. Make sure you have selected Historic 6″ to get the map from ~1840.
Ruth Delany said that she and the crew of Hark were able to identify the start of the route in 1955. Is it still identifiable?