The reservoir, located in the Blessington Lakes in west Wicklow, is used by ESB for hydroelectric power generation.
Its dam structure also plays a critical role in regulating water flow through the Liffey catchment area, namely Wicklow, Kildare and Dublin.
As a result of the consistent rainfall over past two weeks, exacerbated by Storm Chandra, the reservoir is now nearing capacity with water levels having risen by two metres; the state-owned company has said it will need to ease the pressure.
“Over the last number of weeks there has been prolonged and intense rainfall in the River Liffey catchment area, which has significantly increased river and reservoir levels,” ESB said in a statement.
“Large volumes of rain water arrived into the Poulaphouca reservoir in recent days from the upper Liffey catchment area. The vast bulk of this volume has been retained in the reservoir, increasing levels by almost two metres.
Poulaphouca Reservoir.
News in 90 seconds – Saturday, January 31
“Without the dam structures at Poulaphouca, this water would have proceeded through the Liffey from Wicklow into Kildare and ultimately Dublin, significantly increasing water levels all along the river over and above what has been already experienced.”
However, rain has continued unabated in the area since the storm, presenting excess levels of water that will need to be emptied to prevent overflowing.
“As reservoir storage is limited and given current forecasts there may be a need to pass through some of these additional inflows over the coming days,” the statement continued.
“This may increase the risk of flooding along the course of the River Liffey, in particular in the Clane and Newbridge areas. The situation will continue to be closely monitored.”
The company said that a sub-group of the National Emergency Coordination Group has met to coordinate a response with ESB, all relevant Local Authority Severe Weather Assessment Teams, Met Éireann, Government Departments and other agencies.
ESB added: “The Local Authority Severe Weather Assessment Teams are monitoring the situation closely, ensuring resources are in place, that crews are on standby, preparing the necessary interventions and will issue further communications. Individuals with concerns about flooding should contact their local authorities for further information.”