Dredging the Quoile River to deepen it would do nothing to alleviate flooding in Downpatrick, a Stormont report has found.
The review published by the NI Executive examined the causes and impact of the devastating floods last autumn across the south east, devastating parts of Newry, Downpatrick, Newcastle and Portadown.
An “extreme period of heavy rainfall” had left the catchments across the south east saturated and further compounded the already high river levels leading to the autumn 2023 floods.
It is estimated that 600-plus properties were flooded across two council areas — Armagh City, Banbridge and Craigavon, and Newry, Mourne and Down.
The worst affected area in Downpatrick was around Market Street. Heavy rainfall over the Quoile River and Annacloy River catchments from October 26 to November 1 resulted in significant flooding into the low-lying floodplain linked to the Quoile.
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The report said the role that the Quoile Tidal Barrage plays is crucial to understanding the flooding in this area.
It read: “This structure serves a vital purpose as it safeguards the Quoile River floodplain and certain sections of Downpatrick situated below the high tide level from tidal flooding. Without the barrage, the threat of tidal inundation of low-lying areas of Downpatrick, like Market Street, would significantly increase.
“A key limiting factor to the drainage of the Quoile River in Downpatrick is the average level in Strangford Lough which fluctuates with tides. However, in all cases, these water levels are considerably higher than the existing bed levels in the Quoile River. As a result, measures such as dredging the Quoile River to deepen it would be of no benefit.
“As the riverbed is below the level in Strangford Lough, dredging would result in the river filling with water in normal conditions and would therefore not improve the drainage of flood water from Downpatrick.
“During the flood event, the sluices at Victoria Lock in Newry were open to drain water from the canal and hence reduce flood levels in Newry.
“Opening the Victoria Lock gates during the Autumn 2023 flood to allow more water to drain out of the canal was not a viable option as it would require equal water levels each side of the gates to enable them to be opened.”
The report also noted that in Newry “unknown persons removed some sandbags placed along Merchants Quay, which allowed the flood water to reach Lower Catherine Street”.
It also revealed that a wall that collapsed into the Newry River may have helped lower flood levels in the Sugar Island area.
The report found drainage systems “generally lacked the capacity to handle the extreme nature of rainfall that fell over Newry, Newcastle, and Portadown”.
Among the recommendations was developing a “comprehensive flood warning and forecasting system to provide appropriate warnings to communities and businesses at risk and the multi-agency responders”.