River Poddle Flood Alleviation Scheme

Steve Jones, Engineer (Flood Relief Design Section)

Channel Realignment at Whitehall Park Conception (View Downstream)

The River Poddle rises in Cookstown in Tallaght and travels in a north-easterly direction towards Dublin City. It is mainly open channel until it reaches the Grand Canal at Griffith College where it is culverted for 4km and travels beneath the city under Donore Avenue – Newmarket – St. Patricks Cathedral – Dublin Castle and The Olympia Theatre before discharging into the River Liffey.

The Issue

There is a history of both fluvial and pluvial flooding, from the river and the drainage network, on the Poddle over the last 30 years. One event in 2011 resulted in significant flooding in Crumlin and Harold’s Cross and the tragic death of a nurse on Parnell Road. The urbanised and constricted nature of the channel in many locations makes flood risk management challenging.

The Remedy

OPW in conjunction with South Dublin County Council, Dublin City Council and Nicholas O’Dwyer Consulting Engineers have completed preliminary design and reached a significant milestone when a submission was made to An Board Pleanála in 2020. The proposed scheme is designed to provide protection against a 100-year fluvial flood event (1% AEP), will protect approximately 860 residential and 61 commercial properties and will be constructed by OPW direct labour. South Dublin County Council and Dublin City Council are in tandem to correct issues with the drainage network to further protect properties from pluvial flooding.

Proposed Flood Storage Embankment and flow control structure

In layman’s terms the primary solution is upstream storage through the creation of a flood storage embankment and attenuation of the flow with a flow control structure. Think of it as turning the tap to allow for a steady stream of water to be maintained at all times (2-year event) regardless of how full the tank is. This allows for a greater capacity of water to be stored in Tymon Park and for the controlled release of additional water during flood events. The benefits of upstream storage in this case include more manageable construction in open public parklands, reduction in height of flood defences downstream and the bonus that more congested and complex areas previously thought to require intervention downstream will no longer require works.

Two other significant works areas are at Whitehall Park (Templeville Road) where a channel realignment is proposed and at Ravensdale Park (Poddle Park) where flood walls are to be constructed to provide flood protection and additional storage. An Integrated Constructed Wetland (ICW) will also be created in Tymon Park which is to improve water quality, enhance biodiversity, increase amenity value and further attenuate flows.

There has been great collaboration between all teams working on the project. All parties have worked together to ensure the highest OPW and International technical standards are met in the Schemes hydrology, hydraulic, options development and economic appraisal.

Due to the impacts of Covid 19 the deadline for submissions to An Bord Pleanála (ABP) on the Scheme was extended until Monday 11th of May 2020. In July, ABP issued a request for further information (RFI) which was completed and returned on 19th of October 2020. In response to the RFI further submissions were received and a response issued on the 5th of February 2021. The scheme is currently awaiting a planning decision which is expected in Q2 2021.

As a resident in the area, it has been beneficial over the last three years to balance technical and professional elements as an Engineer with stakeholder considerations as a resident. I’ve always considered that if the benefits of the scheme can be proven to me, conveying these benefits and achieving the buyin of other stakeholders and local residents is a much easier task to achieve.

Proposed Flood Storage Embankment and flow control structure

Proposed Channel Realignment at Whitehall Park Conception (View Upstream)

Poddle in Numbers:

• Properties Protected: 921 (Fluvial)

• Projected Cost: €9.5m (Fluvial)

• Planning Route: Part X (Strategic Infrastructure Development)

• Public Consultation: 5 days – 6 locations

• Further information www.poddlefas.ie or info@poddlefas.ie