Pluvial Flooding/Wad River

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Wad River

Project Background & Current Status

There have been a number of historical floods within the river Wad catchment, most recently in 2008, 2009 & 2011 causing severe disruption and flooding damage to the area.  During extreme rainfall events in the catchment the existing pipes and culverts along the Wad became overwhelmed and could not accommodate the increased flows.  This resulted in surface water not being able to enter, and escaping from the River Wad system causing extensive localised flooding in areas such as Collins Avenue, Clanmoyle Road, Howth Road and Clontarf.   

                   Photo of Fig 1: Wad catchment and locations of reported flooding

 Fig 1: Wad catchment and locations of reported flooding

 

Dublin City Council commissioned a study to reduce and alleviate flooding within the Wad River Catchment (from Ballymun to an outfall into Dublin Bay at Clontarf). The Wad Catchment Study report in 2012 recommended that the following specific works be undertaken in a staged fashion:

  1. Sub Scheme 1 – The Clanmoyle Road Flood Alleviation Scheme
  2. Sub Scheme 2 – The Middle Wad Flood Alleviation Scheme

 

  1. Sub Scheme 1 – Clanmoyle Road Flood Alleviation Scheme – This scheme involved diverting flood waters emanating from the river wad away from Clanmoyle Rd and Collins Avenue through a series of underground pipe work and temporarily storing it in an attenuation pond located within the grounds of Clontarf Golf Club.  Once the flood event has passed the retained water is slowly released in a controlled fashion back in to the River Wad. The system is fully automated and is controlled by the automated opening and closing of penstocks monitored by level sensors within the River Wad.    

    Sub Scheme 1 was split into the following 3 separate Works Contracts for construction purposes:

Contract A – Civil Engineering – This work involved laying the upgraded and diversionary pipework, culverts and associated works. The Civils work was undertaken by the OPW and is currently fully complete with the exception of the following:

  1. Landscaping of the Green Area within Clanmoyle Road. This work is being undertaken by a landscaping Contractor in conjunction with the DCC Regional Projects and Flood Advisory Office and DCC Parks and landscaping Section. A Contractor has been appointed and site works have commenced on the 16th April 2018. The Works are anticipated to take 4 weeks to complete.  


Contract B - Golf Course Reinstatement Works – This landscaping contract was carried out by Clive Richardson Ltd. and is fully complete

Contract C - Mechanical & Electrical Works - This contract fully automated the scheme and was being carried out by Veolia Water Ireland. It is fully complete and operational. 

(2)    Sub Scheme 2 – Middle Wad Flood Alleviation Scheme. This Scheme is the next phase in the overall project and involves the following construction works:

  1. Howth Road Crossing – This involves constructing a new culvert across the Howth Road at the junction of the Howth Road and Hollybrook Park. The existing Wad River Culvert at this location is hydraulically limited and needs upgraded. DCC Regional Projects and Flood Advisory Office are currently in the process of procuring Consultant Engineers to produce a full design package for this proposed work.
  2. New Outfall at Clontarf – This work involves providing a new outfall for the wad River at Clontarf. Some advance works relating to this project have been already undertaken and completed during new watermain works at Clontarf Promenade in 2015. The remainder of this work is to be advanced in conjunction with the works at the Howth Road Crossing and similarly DCC Regional Projects and Flood Advisory Office are currently in the process of procuring Consultant Engineers to produce a full design package for this proposed work.

 

Historical Documents

In July 2009, an interim report was carried out by RPS Consulting Engineers.  In December 2009 Nicholas O'Dwyer Consulting Engineers were appointed to carry out a study on the Catchment.


Flood Alleviation Investigations

A data collection exercise was carried out, information from which was used to verify a computerised hydraulic model of historical storm events, such as those of August 2008, July 2009 and October 2011.

Following this, potential generic scenarios for flood alleviation within the Wad catchment were identified. These included;

  • Diversion of Flow Only

  • Piped Conveyance Only

  • Overland Conveyance Only

  • Attenuation Storage Only

  • Non-Structural Measures

More detailed assessments were carried out on all the scenarios based on a number of constraints, such as;

  • Public Acceptance

  • Relative Costs

  • Practicality

  • Health and Safety Issues

  • Planning Issues

  • Traffic Impacts

  • Environmental Issues

  • Programme of Works

  • Existing services and Utilities

  • Buildability & Reliability

  • Long Term Operation

  • Maintenance Issues

None of the above scenarios provided the required flood risk reduction on their own, thus a scheme using the beneficial elements of each scenario/flood alleviation measure was examined and assessed.  The first phase of which is described below, and is called the Clanmoyle Flood Alleviation Scheme.


Clanmoyle Flood Alleviation Proposals

The proposal intends to pipe the flood waters in Clanmoyle Road in the quarry area of the Golf Club, and when the storm abates to release it slowly back into the existing Wad culvert.  There are a number of proposed structures which are required to achieve this and detailed on the planning drawings listed below.

There is also a proposed tunnelled upgrade of the culvert capacity at Howth Road and an additional outfall to the bay alongside Clontarf Road.

The layout of the entire scheme is detailed on planning drawing numbers 20446-PP-01 to 12, downloadable below.

Future Scheme (not part of the recent Planning Application)


Localised works will be required to the west of the M1 in order to alleviate the risk of flooding and there is a proposed new culvert from Collins Park to link up with the proposed culvert on Clanmoyle Road.

Note: It should be noted that when the entire scheme is constructed, the overland flows will be diverted underground at Collins Park, further reducing the risk of overland flows and flooding in the catchment.

The locations of individual components of the schemes are presented in greater detail in the Catchment Report and on the appended drawings, listed below.

Consultations

Following the flooding of August 2008 and July 2009 meetings were held in the local community centre, Le Chéile, following these meetings, further consultations took place with the relevant landowners and stakeholders.  The primary stakeholders, the Clontarf Golf Club, Iarnrod Eireann and Clanmoyle Residents gave approval in principle to proceed with the Part 8 Planning Process, which has resulted in the recent Part 8 Planning Submission.

Dublin City Council’s Law Department and Valuers Department are also engaged in consultation with the relevant landowners, as there are legal items to be agreed, items such as wayleaves.

Liaisons with stakeholders are ongoing, and will continue during the planning process and until construction is complete.

Consultation has also taken place with the Foreshore Unit of the Department of the Environment, Community and Local Government, as a foreshore licence is required to construct the outfall in to the Tolka Estuary.  Further details of this process are described below.

PART 8 Planning Application

The Environment and Engineering Department of Dublin City Council were granted planning permission on the 14th of January 2013 (Application Reference Number: 3161/12).  This approval allows for the first phase to proceed of a wider proposal to reduce and alleviate flooding within the Wad River Catchment to the National Design Standard, the 1:100 year rainfall event.  They are also designed to reduce flooding downstream of the Golf Club in the Castlecourt and Auburn areas. 

The proposal can be summarised into the structures listed below which require planning consent;

  • Inlet structure in Clanmoyle Road green area
  • Pedestrian bridge in the Clontarf Golf Course
  • Retaining wall along the boundary of Clontarf Golf Club and the Dublin-Belfast railway
  • Sports netting around the boundary of the Clontarf Golf Club and properties along Collins Avenue East
  • Inlet and outlet structure in the Clontarf Golf Course
  • Outfall into Clontarf Foreshore

List of Documents And Drawings

The attached documents outline the Wad River Catchment in more detail, and give a greater understanding of the catchment, its geographical area, and the history of flooding within it.  The documents included are as follows;

Clanmoyle Flood Alleviation Scheme – Part 8 Planning Permission.pdf

Wad Drainage Catchment Study - Planning Drawings
(PDF Links to Drawings)

Drawing Number  Drawing Title
20446-PP-01          Overall Scheme Keyplan
20446-PP-04          Recommended Alleviation Works Layout Plan (3 of 6)
20446-PP-05          Clanmoyle Road Alleviation Scheme (4 of 6)
20446-PP-06          Recommended Alleviation Works Layout Plan (5 of 6)
20446-PP-07          Recommended Alleviation Works Layout Plan (6 of 6)
20446-PP-08          Proposed Inlet Structure at Clanmoyle Road
20446-PP-09          Proposed Pedestrian Bridge Structure Details
20446-PP-10          Proposed retaining Wall in Golf Course
20446-PP-11          Proposed Ball catch netting in Golf Course
20446-PP-12          Proposed inlet and outlet Structures

For greater clarity, there are a number of ancillary documents which accompanied the Part 8 documents they are described as follows;


This document primarily outlines the processes which have lead to the application for Part 8 Planning, its approval and why we wish to carry out the Clanmoyle Flood Alleviation Scheme. Our consultant was engaged to carry out an examination of the hydraulic performance of the Wad catchment, and recommend works which would improve flood protection within the catchment.


This report addresses the main EIS (Environmental Impact Statement) themes which were requested by the Planning Department.  This report also includes a Geophysical Survey carried out by Minerex Geophysics Limited.

Appropriate Assessment – Stage 1 Screening Report Rev C
This report is included in the Environmental report, and has been prepared by our consultants to determine the potential impacts, if any, Sub Scheme 1 (Clanmoyle Flood Alleviation Scheme) and Sub Scheme 2 (Middle Wad Flood Alleviation Scheme) may have on nearby sites with European conservation designations (i.e. Natura 2000 sites).  Its conclusions were “No significant impacts on the North Bull Island SPA, the South Dublin Bay SAC, the North Dublin Bay SAC and Tolka Estuary/Sandymount Strand SPA (alone or in combination with other projects or plans) are anticipated.”

Wad River Catchment Study – Catchment Drawings

Drawing Number  Drawing Title
20446 – 01           Overall Catchment Plan
20446 – 02           Survey of Study Areas (1 of 3)
20446 – 03           Survey of Study Areas (2 of 3)
20446 – 04           Survey of Study Areas (3 of 3)
20446 – 05           Areas of Reported Flooding (1 of 5)
20446 – 06           Areas of Reported Flooding (2 of 5)
20446 – 07           Areas of Reported Flooding (3 of 5)
20446 – 08           Areas of Reported Flooding (4 of 5)
20446 – 09           Areas of Reported Flooding (5 of 5)
20446 – 10           Model Output; Flood Plain - August 2008 (1 of 2)
20446 – 11           Model Output; Flood Plain - August 2008 (2 of 2)
20446 – 12           Model Output; Flood Plain - July 2009 (1 of 2)
20446 – 13           Model Output; Flood Plain - July 2009 (2 of 2)
20446 – 14           Model Output; Flood Plain – October 2011 (1 of 2)
20446 – 15           Model Output; Flood Plain – October 2011 (2 of 2)
20446 – 16           Model Output; Flood Plain - 1/100 Year Return Period (1 of 2)
20446 – 17           Model Output; Flood Plain - 1/100 Year Return Period (2 of 2)
20446 – 18           Predicted Flooding For A Joint Tidal / Rainfall Event
20446 – 19           Potential Alleviation Works - Scenario 1 (1 of 2)
20446 – 20           Potential Alleviation Works - Scenario 1 (2 of 2)
20446 – 21           Potential Alleviation Works - Scenario 2 (1 of 3)
20446 – 22           Potential Alleviation Works - Scenario 2 (2 of 3)
20446 – 23           Potential Alleviation Works - Scenario 2 (3 of 3)
20446 – 24           Potential Alleviation Works – Keyplan
20446 – 25           Potential Alleviation Works – Layout Plan (1 of 6)
20446 – 26           Potential Alleviation Works – Layout Plan (2 of 6)
20446 – 27           Potential Alleviation Works – Layout Plan (3 of 6)
20446 – 28           Potential Alleviation Works – Layout Plan (4 of 6)
20446 – 29           Potential Alleviation Works – Layout Plan (5 of 6)
20446 – 30           Potential Alleviation Works – Layout Plan (6 of 6)

 

Application for a Foreshore License

The river Wad discharges to the sea through a culvert outfall at Clontarf Promenade opposite Clontarf Garda Station. As part of the scheme, it is intended to construct a second culvert with a second outfall to the sea. This latter element requires a Foreshore Licence. To that end, Dublin City Council applied to the Department of Environment, Community and Local Government (DOECLG) for a Foreshore Licence. The minister signed and approved the draft Foreshore Licence and it has now being referred to the Chief State Solicitors Office and Dublin City Councils Law Agent for final drafting.
 

                 Photo of Figure 2 – Impression of proposed culvert along Clontarf Foreshore

 Figure 2 – Impression of proposed culvert along Clontarf Foreshore

The proposed new outfall is a new box culvert to be constructed under the grassed area of the Clontarf Promenade, from the bus lane of Clontarf Road to the foreshore. The new culvert is to be located alongside the existing underground Wad River Culvert. Its aim is to increase the carrying capacity of this section of the Wad network and thus reduce flooding upstream.

Drawings and Information

Where do we go from here

  • Legal wayleave agreements are to be reached with the relevant stakeholders and residents
  • Finalise Foreshore Licence
  • Construction phase funding in place
  • It is expected that construction works will be carried out by the OPW, with works programmed to commence later this year / early next year, subject to way leave agreements.

Information last updated October 2013

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