Hugh Montgomery's "green" found in Newtownards / the day Newtownards got flooded

It's effectively the first recorded golf course and football pitch in Ireland, beside the "great school" which Hugh Montgomery had built in Newtownards around 1620. In the latest edition of Ulster Folklife (Vol 54), historian Andrew Steven analyses all of the documentary and topographical evidence and concludes that it was in the area now known as Movilla Street and Greenwell Street. The school principal was John McClelland, who was one of the four ministers on board the emigrant ship Eagle Wing in 1636.

PS: As an aside, local folk will remember the day in the early 1980s when Strangford Lough, after centuries of retreat, suddenly reverted to its ancient high water mark and just kept coming in, flooding the flat ground of the whole Portaferry Road area, right up as far as the Old Priory where the Montgomeries had built the school and also their first house. The present-day floodgates were built shortly after this incident - but back in 1744, Walter Harris wrote that "the old house of the Mountgomery family stood pleasantly seated on the edge of the Lake". I'm trying to find the precise date of the flood - any help would be appreciated.