Re: Severn tunnel is "wet" - but salt or fresh?


"Cathode Ray" <RBCatlow@xxxxxxx> wrote in message
news:26f9cd08-6c45-4bd6-81d6-e41ff65e1c2d@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I had the opportunity to visit the Sudbrook complex for a few days to
undertake some transformer testing a little over a year ago and was
given a full tour of the site - it is engineering on a wholly
spectacular scale.

As David has pointed out, the tunnel is kept dry by a number of
pumping stations:

Sudbrook 1, 2 and 3 are at the actual pumping station itself, Sea Wall
is on the English side and 5 Miles 4 Chains is further west of
Sudbrook itself.


From the notes that I made during my visit:

Salt water seepage into the tunnel is realtively slight and occurs
mainly at the English end. Sea Wall pumping station pumps any
rainwater from the trackbed as well as the seepage from the tunnel and
discharges this directly into the Severn. Two submersible pumps are
located at this site.

Sudbrook 1, 2 and 3 contain the inflow of water from the Great Spring,
using fourteen submersible pumps that are located at the lowest end of
the risers. The water is potable and some of it is sold for further
use, the remainder is discharged into the Severn.

5 Miles 4 chains pumping station controls the rainwater that collects
at the Welsh end and that contributed by another, minor spring and the
water is discharged into the local sewer by another two submersible
pumps.

Despite the incredulity of Mr Polson, I was told that the nadir of the
tunnel would flood fully within 30 minutes if the pumps at Sudbrook
failed. I was told this when I was standing in the adit underneath
the running tunnel that collects the spring water and that the adit
would flood within 3 minutes in the event of a total pump failure - a
bit sobering given the speed of the lift that provided access.

At the time of my visit ( Febrary 2007), Sudbrook 1,2 and 3 were
pumping 37 million litres of water a day. The amount pumped depends
largely on the surrounding water table which feeds the great spring.
During the summer of 2006, the smallest amount pumped was 22 million
litres per day. The highest level within the recent past was 45
million litres per day.

The electrical distribution system is comprehensive and there are five
standby generators located around the Sudbrook site and another two at
Sea Wall to ensure that the pumps can still operate in the event of a
total incoming power outage. The whole system is supervised 24 hours a
day from the control room at Sudbrook.

As can be imagined, the ongoing maintenance of the pumps and subsidary
systems is significant and there are sizeable machine shop and
workshop facilities at Sudbrook and a permanent staff of around 20 or
so M&E engineering staff on site.

The market for the spring water is now very much reduced. As others
have commented, there used to be sizeable industrial consumers for the
water in the form of the Magor brewery, St Regis paper mill and the
steel industry, as well as supplying the neighbouring area with
domestic water supplies.

At the time of my visit, the spring water was only supplying the local
community and the Magor brewery - the paper mill has closed and the
site no longer supplies the steel industry. Network Rail was and is
seeking alternative uses for the water. Reduced extraction of
groundwater in the surrounding area by heavy industry is leading to
the need to pump more water from the Great Spring.

I weas shown an interesting British Transport Film on the subject of
Sudbrook and the construction of the Severn Tunnel during my visit. It
shows the last days of the steam pumping engines (apparently Sudbrook
had the largest concentration of a particular type of engine anywhere
in the world), before electric pumps were installed in the late 50's
early 60's, it may be available for purchase from the BTF archives.

Ray

I believe the original pumps were low-pressure Cornish beam-engines- one is
to be seen (I hesitate to say 'preserved') at the South Wales Industrial
Museum in Swansea.
Brian


.

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