COMHAIRLE CONTAE ÁTHA CLIATH THEAS
SOUTH DUBLIN COUNTY COUNCIL

MEETING OF LUCAN AREA COMMITTEE

Tuesday, October 28, 2014

QUESTION NO. 17

QUESTION: Councillor P. Gogarty

"To ask the Chief Executive for an update on matters discussed at last months ACM regarding proposals for a pedestrian bridge across the Griffeen in Lucan village; especially with regard to what further contacts/discussions, if any, have taken place between the relevant Council departments regarding guarantees to ensure the bridge maintains the same levels of flood protection as currently given by the raised wall; given that climate change projections suggest increased heavy precipitation increasing the likelihood of the "one in 100" year floods such defences have been built for; and if he will make a statement on the matter?"

REPLY:

The proposed bridge across the Griffeen River in Lucan Village is at a very early stage of design and requires further detailed design and assessment. In any detailed proposal the Council will seek to maintain the existing conveyance and storage capacities of any existing channels. The design and construction of any bridge will be such that flood risks up- and / or down-stream are not increased, or, where no other viable options exist, are restricted to acceptable levels, and will comply with any flood risk management objectives and plans established for the area. In this respect any information or modelling available from CFRAMS [Catchment Flood Risk Assessment and Management ] will be used to establish the viability and effect of any design.

The consent of the OPW is required by bodies and persons proposing to carry out construction/alteration works on bridges and culverts under Section 50: Arterial Drainage Act, 1945 and EU (Assessment and Management of Flood Risks) Regulations SI 122 of 2010. The OPW may consent to alterations to existing watercourses or structures if the proposed works would not increase the risk of flooding, or will not have a negative impact on drainage of land.

In general, a proposed bridge or culvert design submitted with an application under Section 50 should demonstrate the achievement of the following design standards:

A bridge or culvert must be capable of passing a fluvial flood flow with a 1% annual exceedance probability (AEP) or 1 in 100 year flow without significantly changing the hydraulic characteristics of the watercourse.

A bridge must be capable of operating under the above design conditions while maintaining a freeboard of at least 300 mm.

If the land potentially affected includes dwellings and infrastructure, it must be demonstrated that those dwellings and/or infrastructure are not adversely affected by constructing the bridge or culvert. 

In the event that any developed design for the bridge does not meet the appropriate criteria the development as proposed will not proceed.