William Ockenden has been described as a Dutch engineer who worked on three eighteenth century Irish navigations: the Mallow to Lombardstown canal, the Kilkenny/Nore navigation and the Limerick Navigation [Park Canal section], all of them notably unsuccessful.
It seems likely that he was English, not Dutch, but may have lived in Ireland before inheriting property in England. But was he an engineer or a mill-owner and MP? Were there one or two William Ockendens at the time?
Here is some information and some speculation. I would welcome more of the first.
Irish waterways history 
Sirs, Do you have any information on the Roscommon canals?
1) Proposed extension of Royal canal to Roscommon town.
2) Proposed canal from Athlone to Rosocommon town.
3) Proposed canal to the River Suck.