Thunderstorm downpour led to sewage overflow at weir

A HEAVY downpour of rain this week led to a sewerage network overflowing and flooding into Balrothery Weir.

On Monday night, heavy rainfall and thunderstorms resulted in a manhole located on a green space near the Balrothery Weir – or Firhouse Weir as it’s known locally – surcharging.

Surcharging happens when the carrying capacity of a sewer system is overloaded as a result of inflow and infiltration.

The Dodder Valley sewer is part of Uisce Eireann’s wastewater network in the Dublin region.

“On the evening of Monday, May 8, following very heavy rainfall and thunderstorms over a short period of time (Yellow weather warning in place), a Dodder Valley sewer surcharged near Firhouse Weir in Dodder Valley Park,” a spokesperson for Uisce Eireann, formerly Irish Water, told The Echo.

“Due to the unprecedented nature of the storm and the sheer volume of rainfall in a very short period of time caused a release on our network.

“Uisce Eireann has been liaising with South Dublin County Council, the [Environmental Protection Agency] EPA and Inland Fisheries Ireland in relation to the overflow, and a clean-up is being carried out in the area by South Dublin County Council.

“Uisce Éireann regrets any disruption to the local community caused by this issue.”

Surcharging of the Dodder Valley sewer is an issue which, despite over €5m being invested by South Dublin into the Dodder Greenway at the park, is ongoing.

At times of heavy rain, and when the system reaches peak capacity, there is the risk of wastewater overflowing into Dodder Valley Park– and towards one of the city’s most important, biodiverse waterways, the Dodder.

This is what happened in February 2021 when heavy and persistent rain resulted in a serious volume of wastewater and debris gushing into a stretch of parkland between the weir and Cherryfield.

In September 2022, Irish Water said that it “was testing the existing network against current design flows and future predicted flows out to a 25- year design horizon”.

At that time, it made a commitment to work with the council in relation to “investigating and removing misconnected flows that have resulted in large areas of paved area being connected to the foul sewer”.

This cropped up after the manhole surcharged, and heavy flooding occurred at the weir, which had been renovated as part of the Dodder Greenway project and was ultimately damaged.

A newly laid pathway was damaged and washed away, with the council later repairing it.

However, when the heavy rainfall occurred this week, the sewer drainage surcharge happened once again at the location.

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