Page 37 - Gi flipbook September 2018

I requested that a feasibility study be
undertaken. Included in this was: a FIGURE 1 View from the centre of the river, on the left is the steep banks of the TLHB
GPS topographical survey, where the major erosion is occurring and also where there is a whirlpooling effect
environmental studies on both sides
of the river and some high level
design ideas for best value protection
of the pipeline. Through evaluation of
this study and other projects of this
nature, it was decided that the most
viable course of action would be a full
river bank remediation/river diversion.
The current state of the river bank
is shown in Figure 3, where it is
evident the river is eroding a huge
hole in the TLHB (true left hand bank)
and it is only getting worse.
The pipeline in jeopardy is known as
a T/SP/P/18 pipeline, meaning that the
weld records are not available
anymore. Due to this fact, emergency
procedures would be applied if the
pipeline were to be exposed; line
pressure would likely be reduced by
15 per cent as a precaution and the
welds would need to be excavated
and checked by specialists, who would
make a decision on their quality
against pipeline specification T/SP/P/11.
If these did not meet the industry FIGURE 2 Aerial view of the River Mersey project, showing the direction of the water flow
standard, remedial action would be (top right to bottom left), The Waterside Hotel, National Grid pylons, Cadent HP pipeline,
necessary. This would usually take the Network Rail and M60 Motorway
form of an epoxy shell applied to the
weld to strengthen it. This procedure
is costly, so should be avoided if
possible. If the pipeline were to be
undermined, the total cost of the
procedure and shelling would be in
the region of £350k. Additionally,
action would still be required to
address the issue of the river with a
project like this one.
It is obvious that the erosion spot
around the middle of the drawings is
a huge issue. To add to this, there is a
section of concentrated invasive plant
species – Japanese Knotweed, Giant
Hogweed and Himalayan Balsam
– these will need to be dealt with
during the works.
The grey shape in the water channel
is composed of river silts and sands
deposited due to the drop in energy
on an inside bend of the river. This is
the start of another migration of the restriction for any machinery. THE SOLUTION
river; the small channel between the The Waterside Hotel, which sits on Excavation of the old channel to
TRHB (true right hand bank) and the the light grey area of the inside bend, divert the majority of the flow of
silt bar will eventually close and force owns the land through which we will water will allow for a safe work area
all the water to be pushed further require access. The access road to the to commence remediation of the
outwards. This is a completely natural car park is also in danger of erosion TLHB. Works can then start on the
process, but will only make the and collapse, so an agreement has TRHB, where we will undertake this
erosion near the pipeline worse. been made with the owners regarding excavation of the old channel. We will
Another challenge is that National further separate works. On the other build up a small section at the top and
Grid have 400kV overhead cables side of the river there is a farmer who bottom of the channel to act as a
that run directly above the main uses this field mainly for grass, but dam. When the TRHB has been
works area creating a height sometimes for cattle. constructed with rock armouring and

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