Breagh Development - RWE.com

Breagh Environmental Statement
Section 2 – Proposed Development
Figure 2-8 Trailing Suction Dredger (DEME, 2010)
The 3” MEG pipeline and FO cable
will be laid separately from the
production pipeline at a distance
of approximately 50 m and will be
trenched along their entire length
to offer dropped object and fishing
gear protection. The trench, which
will be allowed to naturally backfill,
may be cut with a plough or a
water jet trencher. Of these two
options the plough has a larger
subsea footprint. From a distance
of 12 km offshore to landfall the 3”
MEG line and FO cable will be
trenched following the same methodology utilised for the 20” production pipeline. Table 2-
7 summarises the area impacted by the trenching operations.
Table 2-7 Subsea footprint associated with trenching
3” MEG
Pipeline &
FO cable
20”
Production
pipeline
2-14
Trench Section
Distance
(km)
Width of seabed
impacted (m) Subsea
footprint (km 2 )
Trench Storage
Nearshore trench 12 30 30 0.72
Offshore trench 88 20 1.76
Nearshore trench 12 30 30 0.72
TOTAL 112 - 3.2
Two cables must be crossed by the pipeline en-route to TGPP (Figure 2-9). Prior to pipelay, 4
mattresses measuring 2 x 5 m will be installed at each cable crossing. Post lay protection will
be provided by rockdump or mattress laying. If mattress laying is required for protection an
additional 4 mattresses will be laid at each crossing location. If rockdumping is required 200
tonnes of rock will be dumped per crossing. The footprint of each cable crossing will be
approximately 200 m 2 . Figure 2-10 illustrates a typical crossing protected by rockdump.