COMHAIRLE CONTAE ÁTHA CLIATH THEAS
SOUTH DUBLIN COUNTY COUNCIL

MEETING OF SOUTH DUBLIN COUNTY COUNCIL

Tuesday, May 07, 2019

HEADED ITEM NO.12(a)

HEADED ITEM: UPDATE ON THE RIVER PODDLE FLOOD ALLEVIATION SCHEME

REPLY: 

6km in length rises in Tallaght flowing through Tymon Park, KCR, Harold's Cross, Blackpitts and discharges at Wellington Quay

History of Scheme:

• Recent major flood events recorded in 1986, 2000, 2008 and 2011
• Identified in OPW Eastern CFRAMS 2011 Report
• River Poddle Options Report 2014
• Storage in Tymon Park combined with flood defences
• Approval for funding provided by OPW in 2017
• SDCC Lead Authority in Tri agency scheme with DCC and OPW
• Nicholas O’Dwyer Ltd appointed as consultants in March 2018
• Scheme launched by Minister of State Kevin ‘Boxer’ Moran in October 2018

Poddle Catchment Data:

• Catchment Area: 15 km2
• Open channel upper catchment
• Mostly culverted lower catchment
• Catchment drains into River Liffey at Wellington Quay via surface water system
• Heavily urbanised watercourse
• Mostly open channel from ITT through Tymon North, M50, Tymon Park to Kimmage
• Piped surface water drainage system from Harold’s Cross, under Grand Canal to City Centre
• Flooding issues in the River Poddle Catchment have been frequently documented in previous years. The River Poddle has overflowed its banks at several locations and back up the drainage system posing a risk to human life.
• On October 2011 a major flooding was reported along river Poddle. The rainfall depth exceeded the 2% AEP (1 in 50 year event).
• The river Poddle hydraulic model was constructed in 2011 as part of the Eastern CFRAM study using the InfoWorks ICM software.

Main Objectives:

• Update/modify/correct the existing hydraulic model to best represent the current drainage layout of the River Poddle catchment
• Model a range of design events and undertake a detailed analysis to complete a design for Poddle Flood Alleviation Scheme
• Prepare Environmental Impact Assessment Report (EIAR), Part 10 Planning Documentation;

Design Standards:

• There should be no flooding from surface water pipelines for a return period of fewer than 30 years.
• There should be no property flooding from river flows for a return period of fewer than 100 years.
• There should be no property flooding from tidally influenced rivers for a return period of fewer than 200 years

Works to Date:

• Full Hydrological Analysis of the Poddle catchment
• Full Hydraulic analysis of the River with a range of blockage scenarios
• Environmental Impact Assessment and Preliminary Design Reports currently being finalised for Part X Application
• Construction Environmental Management Plan
• 4 Public Information Sessions held in December 2018
• Range of surveys completed including
• Topographic and Threshold
• Structural Condition
• CCTV surveys of Culverts

Scheme Proposed:

• Increase storage at Tymon Lakes to reduce outflow downstream with a 200m long embankment.
• Create additional flood storage at Wainsfort/Manor Green and Ravensdale Park (DCC)
• Build flood defence embankments and flood walls along river course at vulnerable locations
• Embankments to include 500mm freeboard, flood walls: 300mm
• Clear trees and vegetation where defences are being installed
• Upgrade culvert screens and screen maintenance mechanisms
• Rehabilitate existing flood defence walls, structural assessment and replacement as required of existing walls along river route
• Develop Asset register of River Poddle Flood Defences for SDCC/DCC Development Plan
• Estimated flood defence lengths greater than 2,100m

Future:

• Part X Planning Application estimated to be submitted to An Bord Pleanala in June 2019 
• Submit Designs, Layouts, Environmental Impact Assessment Report and Natura Impact Statement
• Minimum 6 week Public Consultation for Submissions
• Possible Oral Hearing
• 18 weeks decision time from date of last submission
• Construction forecasted to start in Q4 2019/Q1 2020 subject to planning approval
• 24 Month Construction Period