Comments on relevant observations to the foreshore application

for the Rockabill subsea cable system ref: FS006842

From The Portrane Beach Group (25th July 2018)

Obs. - The Foreshore Ecosystem.

1. The application for the Foreshore Licence is based on prior experience in designing landfalls

and in the installation of subsea cables together with a careful assessment of any potential impacts

on the Portrane foreshore environment and ecosystem through the compilation of the Natura 2000

Impact Statement, Marine Archaeological Assessment Report and Planning Report. The Planning

Report sets out in detail the various aspects and methodologies for the installation of the cable

itself. The key points to note in regard to potential impacts on the foreshore ecosystem include;

The installed cable is only 39mm in diameter – less than 2 inches in width.

At the landfall, the cable will pass beneath the coastline in a pre-installed Horizontal

Directional Drill Duct and this will extend to a point at 60 metres from the coastline.

Seaward of the end of the Horizontal Directional Drill the cable will be installed below the

surface of the beach using a specialised subsea cable plough. This plough will trench and

install the cable in a single continuous operation which will temporarily disturb the surface

of the seabed over a width of 750mm. The area influenced by the installation of the cable is

localised and the disturbance of the seabed is temporary.

Within the intertidal zone (between the low water mark and the end of the HDD duct) the

ploughed cable trench will be reinstated by back blading with the bulldozer in the first

instance. Natural wave action will complement this over the following tidal cycle.

2. The general experience with a sandy seabed such as that at Portrane is that the

beach/seabed profile across the narrow cable trench is largely restored by the natural wave action

of the advancing tide, mostly in one tidal cycle and is fully restored over a short period of time.

Experience at Sandymount, Sutton and for 3 cable landfalls at Southport in the UK has confirmed

this to be the case and in no case has there been any permanent physical, environmental or

ecological knock-on effects.

Obs. - ‘The Quay’ Portrane.

3. The beach at Portrane is flat and sandy and the distance between the High Water Mark and

the Low Water Mark is approximately 600 metres at the proposed landfall location. The Admiralty

Chart data shows the beach drying to 1.3 metres Chart Datum at low tide.

4. The bearing of the proposed route is 80⁰/260⁰. At the shore end the route is 45 metres from

the section of coastline opposite the access to Seaview Heights at the area locally known as ‘The

Quay’ at Latitude: 53°29'37.38"N Longitude: 6° 6'28.26"W. This offset increases to 170 metres at the

headland (Latitude: 53°29'40.97"N Longitude: 6° 5'55.18"W. (Figure 1).

Figure 1. ‘The Quay’ Portrane.

45 metres

170 metres

‘The Quay’ Portrane

Obs. - Existing Sheet Pile Wall and proposed future coastal protection works.

Existing sheet pile wall –

5. The location and extent of the existing sheet-pile wall are shown on Figure 2 from

information provided to the Fingal Council Coastal Liaison Group and this has been cross-referenced

with Google Earth (Figure 3) and with observations on site (Figure 4).

Figure 2 Fingal Council Coastal Liaison Group, Meeting No 3, 22nd February 2017

Figure 3 Google Earth Imagery of the landfall location

Existing sheet pile wall

within grassed area above

high water mark

Proposed Route and heading of

Rockabill cable system

Termination point of existing

sheet pile wall – adjacent to

ESB pole within grassed area

outside foreshore extents

ESB utility pole

6. The extent of the sheet pile wall together with the planned cable route at the landfall, are

shown in Figure 5 (SK 1319-A-013).

Figure 4. Site photograph of extent of existing sheet pile wall.

Termination point of

existing sheet pile wall

within grassed area

ESB utility pole

Figure 5. Onshore Cable Routing at the Landfall (Based on Drawing 1319-A-008).

7. The line of the planned cable route is an extension of the inshore routing on the foreshore

as shown in Drawing 1319-A-008 which formed part of the Foreshore Licence Application. As can be

seen in Figures 3 to 5, the proposed cable route lies to the south of the sheet pile wall and is clear of

the termination point at the southern end.

Proposed future coastal protection works -

8. Fingal County Council have engaged RPS Consulting Engineers to assess coastal erosion at

Portrane, in particular at ‘The Burrow’, an area of sand dunes approximately 300 metres north of the

proposed landfall location for the Rockabill cable system and to propose a series of measures for

future coastal protection works. The southern end of Portrane Beach (Zone 3, Section 3.2) is also

included in the study and a check has been made with RPS Consulting Engineers on their proposals

and on any further sheet piling that may be proposed at the southern end. They have confirmed that

“there is no new sheet piling included within the current proposed works”.

9. Notwithstanding this, if it were to be decided at a future date to extend the existing sheet-

pile wall southwards after the cable is installed, a benefit of the use of a Horizontal Directional Drill

at the landfall would enable a relatively simple localised engineering solution to be developed.

Accordingly, the extension of the sheet-pile wall would not be inhibited by the installation of the

cable at the proposed landfall.

Obs. - Pre-Lay Grapnel Run – obstacle clearance.

10. The Pre-Lay Grapnel Run (PLGR) is carried out to clear the path of a cable on the seabed of

debris such as abandoned nets, ropes or hawsers before the final installation. The PLGR generally

extends to a depth not exceeding 600mm below the sea-bed and it extends seaward from the 10

metre water depth contour. At Portrane, the 10 metre water depth is 2.225kms from the coastline.

As in the case of the cable plough, the pre-lay grapnel run will disturb the seabed over a width of

approximately 600mm and reinstatement takes place naturally with the action of tides and currents

over a short period of time. The area influenced by the pre-lay grapnel run is localised and the

disturbance of the seabed is minor and temporary.

11. The installation of the fibre optic cable in the sea-bed is not significant engineering works. It

is a transient, localised and low physical impact operation and involves temporary disturbance of a

narrow strip of sea-bed with natural reinstatement taking place within an extremely short time

period. This has been the case at Baldoyle, Sutton, Dollymount, Sandymount and at landfalls at

Wexford, Cork and Mayo and also at a series of landfalls on the west coast of the UK. In no case has

there been any long term physical, environmental or ecological knock-on effects.

General Comment

12. The proposed cable route and landfall site lies to the south of the dune system at ‘The

Burrow’ at Portrane. The line of the cable also lies to the south of the existing sheet-pile wall and is

clear of it. The line of the cable route is 45 metres off the coastline at ‘The Quay’ and this offset

increases to 170 metres at the headland.