I use the Lynmouth floods as the basis for a discussion with students
about what you should design bridges for.
The Lynmouth flood was exceptional on many levels. It is well described
in a paper in the Inst of Civil Engineers. THE LYNMOUTH FLOOD OF AUGUST
1952.C H DOBBIE
<http://www.icevirtuallibrary.com/search;jsessionid=322h917lumetu.x-telford-live-01?value1=&option1=all&value2=C+H+DOBBIE&option2=author>;
P O WOLF,
<http://www.icevirtuallibrary.com/search;jsessionid=322h917lumetu.x-telford-live-01?value1=&option1=all&value2=P+O+WOLF&option2=author>ICE
Proceedings: Engineering Divisions
<http://www.icevirtuallibrary.com/content/serial/ipeds;jsessionid=322h917lumetu.x-telford-live-01>,
Volume 2, Issue 6
<http://www.icevirtuallibrary.com/content/issue/ipeds/2/6;jsessionid=322h917lumetu.x-telford-live-01>,
01 December 1953 , pages 522–546.
For those who don't know the background, Devon gets lots of storms
coming in from the Atlantic, many of which are quite localised. The
rivers that flow north into the Bristol Channel are very short, and very
steep, which means they have very short rise times - a few hours max.
There was a very intense storm on 15th Aug 1952 over Exmoor, with as
much as 250 mm rain in a short period (there is no exact data because
there were very few gauges); this figure was obtained by back
calculation. About half of the area drained into the East and West Lyn
rivers, which are less than 10 km long, and produced run off intensities
of about 7 m^3/s/km^2 from a catchment of about 100 km^2, which compares
with the expected mean annual flood of about 0.4 m^3/s/km^2. The
village had started life as a small fishing community as an adjunct to
Lynton (which lies on the high ground above the valley), but had
expanded into a resort in Victorian times, much of it built on the only
flat land available, which was next to the river and in reality was part
of its natural flood course. The river reclaimed its own and washed
away many buildings with great loss of life (it struck at night while
many people were in bed). The village was rebuilt with a much wider
channel and much bigger bridges. My father was an engineer and worked
on the rebuilding.
The 1952 storm was described as a "1 in 1000 years event", but
interestingly there was another flood in about 1956/7 that was almost as
high. I have seen it described as a "1 in 975 year event" in a paper
that I can no longer find but would love to be able to get hold of, but
this caused no problems because a much bigger channel had been
provided. My father described seeing the water only a few inches below
the soffits of the new bridges. I use this example to show students
that just because you have had one very rare event, it doesn't mean that
you can't have another very soon afterwards.
There are reports of a similar flood about 150 years earlier, and there
have been other floods nearby, notably at Boscastle in Cornwall, which
has a similar river profile and catchment.
I agree with Andrew that the RAF were almost certainly not responsible
for the flood. They were apparently seeding clouds over Salisbury
Plain, well to the east, and the storm came from the west. But mud
sticks and geoengineering is expected to disrupt climate patterns, which
makes even more clear that we should do the research to find out what
the issues are and then get the governance sorted out before we attempt
anything for real.
Chris Burgoyne
On 17/02/2015 11:15, Andrew Lockley wrote:
Poster's note : this historical news piece almost certainly
incorrectly points the finger of blame - a large low pressure system
and a cold front combined to cause the flood. Nevertheless, it's
instructive of the controversies we can expect in a geoengineered world.
RAF rainmakers 'caused 1952 flood'
http://gu.com/p/pvtn
John Vidal and Helen Weinstein
Published: 10:56 GMT+01:00 Thu 30 August 2001
On August 15, 1952, one of the worst flash floods ever to have
occurred in Britain swept through the Devon village of Lynmouth.
Thirty five people died as a torrent of 90m tons of water and
thousands of tons of rock poured off saturated Exmoor and into the
village destroying homes, bridges, shops and hotels.
The disaster was officially termed "the hand of God" but new evidence
from previously classified government files suggests that a team of
international scientists working with the RAF was experimenting with
artificial rainmaking in southern Britain in the same week and could
possibly be implicated.
Squadron Leader Len Otley, who was working on what was known as
Operation Cumulus, has told the BBC that they jokingly referred to the
rainmaking exercise as Operation Witch Doctor.
His navigator, Group Captain John Hart, remembers the success of these
early experiments: "We flew straight through the top of the cloud,
poured dry ice down into the cloud. We flew down to see if any rain
came out of the cloud. And it did about 30 minutes later, and we all
cheered."
The meteorological office has in the past denied there were any
rainmaking experiments conducted before 1955, but a BBC Radio 4
history investigation, to be broadcast tonight, has unearthed
documents recently released at the public record office showing that
they were going on from 1949 to 1955. RAF logbooks and personnel
corroborate the evidence.
Until now, the Ministry of Defence has categorically denied knowledge
of any cloud-seeding experiments taking place in the UK during early
August 1952. But documents suggest that Operation Cumulus was going on
between August 4 and August 15 1952. The scientists were based at
Cranfield school of aeronautics and worked in collaboration with the
RAF and the MoD's meteorological research flight based at Farnborough.
The chemicals were provided by ICI in Billingham.
Met office reports from these dates describe flights undertaken to
collect data on cumulus cloud temperature, water content, icing rate,
vertical motions and turbulence, and water droplet and ice crystal
formation. There is no mention of cloud seeding.
But a 50-year-old radio broadcast unearthed by Radio 4 describes an
aeronautical engineer and glider pilot, Alan Yates, working with
Operation Cumulus at the time and flying over Bedfordshire, spraying
quantities of salt. He was elated when the scientists told him this
had led to a heavy downpour 50 miles away over Staines, in Middlesex.
"I was told that the rain had been the heaviest for several years -
and all out of a sky which looked summery ... there was no disguising
the fact that the seedsman had said he'd make it rain, and he did.
Toasts were drunk to meteorology and it was not until the BBC news
bulletin [about Lynmouth] was read later on, that a stony silence fell
on the company," said Mr Yates at the time.
Operation Cumulus was put on hold indefinitely after the tragedy.
Declassified minutes from an air ministry meeting, held in the war
office on November 3, 1953, show why the military were interested in
increasing rain and snow by artificial means. The list of possible
uses included "bogging down enemy movement", "incrementing the water
flow in rivers and streams to hinder or stop enemy crossings", and
clearing fog from airfields.
The documents also talk of rainmaking having a potential "to explode
an atomic weapon in a seeded storm system or cloud. This would produce
a far wider area of radioactive contamination than in a normal atomic
explosion".
UK weather modification experiments at the time presaged current
practice in the US. The idea was to target "super cool" clouds, and to
increase the volume of freezing water vapour particles. Most methods
involved firing particles of salt, dry ice, or silver iodide, into
clouds, either from an aeroplane or from burners on the ground. The
clouds would then precipitate, pulled down below freezing point by the
extra weight of dense particles, thus making it rain sooner and
heavier than it might have done. Significantly, it was claimed that
silver iodide could cause a downpour up to 300 miles away.
Many countries now use the technology, which has considerably improved
during the past 50 years.
But controversy still surrounds the efficacy of these early
cloud-seeding experiments. In 1955 questions were asked in the Commons
about the possibilites of liability and compensation claims. Documents
seen by the BBC suggest that both the air ministry and the Treasury
became very anxious and were aware that rainmaking could cause damage,
not just to military targets and personnel, but also to civilians.
The British Geological Survey has recently examined soil sediments in
the district of Lynmouth to see if any silver or iodide residues
remain. The testing has been limited due to restrictions in place
because of foot and mouth disease, and it is inconclusive. However,
silver residue has been discovered in the catchment waters of the
river Lyn. The BGS will investigate further over the next 18 months.
Survivors of the Lynmouth flood called for - but never got - a full
investigation into the causes of the disaster. Rumours persist to this
day of planes circling before the inundation.
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