The Flood Risk in Perth, Scotland.
David Crichton, October 2012.
General
The River Tay, with a catchment area of some 5,000 square kilometres (a quarter the size of Wales)
has the largest peak flow of any river in the UK, as recorded at the Ballathie gauging station just north
of Stanley. The peak discharge is the equal of the flows of the Clyde, Thames and Severn combined.
The Tay is tidal as far as the North Inch, just North of Smeaton’s Bridge. The largest known flood
recorded in Perth was on 17 February 1814 when the level at Smeaton’s bridge reached 7 metres
above Ordnance Datum. In February 1990, the river level reached 5.85m above Ordnance Datum. In
January 1993, it reached 6.48 above Ordnance Datum. Habitation in Perth can be traced back for
thousands of years when Perth was a fording point for the river Tay. The big riverside parks are
called “inches”, meaning “island” in Pictish and the North Inch and South Inch were gifted to the
people of Perth by King Robert III in 1377 on condition that he be allowed to be buried in St John’s
Church. The people joked that he wanted six feet in exchange for two inches. (In the end he was
buried in Paisley.)
The Tay Bridges in Perth
In 1209, a bridge at the foot of Perth High Street was swept away by floods. It must have been rebuilt
soon after, because a record exists of King Alexander II meeting his father's funeral cortege at the
bridge of Perth in 1214. In 1317 the bridge was mentioned in a charter of Robert the Bruce, and in
1328 he asked the Abbot of Scone to allow stones to be taken from Kincarrathie Quarry for repairs to
the Bridge of Perth and the Bridge of Earn. During the 14th, 15th and 16th centuries there are
numerous references to the bridge needing repairs and towards the end of the 16th century it became
obvious that a new bridge had to be built.
Smeaton’s Bridge, completed in 1771, is a nine span masonry bridge with seven piers in the river
channel. John Smeaton, architect of the Eddystone Lighthouse, designed an extremely strong bridge
with a very high soffit, high enough to allow major flood flows and withstand ice dam build up. It has
survived many extreme flood events, and today carries much more traffic than Smeaton could ever
have imagined.
Perth railway bridge was built in 1863 to replace a wooden structure built 14 years earlier. It was
designed by the Caledonian Railway Company to carry the single track of the Perth - Dundee line.
The bridge is supported by iron girders (where it passes over the river) and stone arches (over
Moncreiffe Island). The span nearest the west bank of the river was originally designed to swing open
to allow shipping to pass further upriver. Such traffic ended in the late 19th century. The soffit is above
expected water levels and the piers do not represent a major constriction. The railway viaduct spans
both channels on either side of the 46 hectare Moncrieffe Island. The bridge includes a public
footpath with stairs leading down to Moncrieffe Island. At high tide, it is the only way to reach the
island other than by boat. There is a causeway to the island which can only be used at low tide.
The Queen's Bridge was opened by Queen Elizabeth II in October 1960, to replace the Victoria
Bridge. In order to keep the crossing open during construction, the steel framework of the old bridge
was jacked up 6 feet while the new bridge was built beneath it. Queen’s Bridge is a two pier concrete
structure with a curved soffit. During the 1993 event the water level was hitting the bridge soffit above
the west pier and causing a standing wave to form at the bridge face resulting in considerable
turbulence. The bridge was closed to traffic due to fears of possible collapse.
A chronology
1210 Scone palace and much of the town swept away. King William escaped in a small boat but his
son was drowned.
1604 In 1604 King James VI engaged his Master Mason John Mylne to build a new bridge to the
north of the old site. The work was hampered by flooding and freezing of the river, but the keystone of
the final arch was laid in 1616. Unfortunately, Mylne's bridge was rather low, and very vulnerable to a
rise in river level.
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14 October 1621 In 1621 there was a great storm which lasted three days, and a terrible flood which
made many homeless, destroyed the town's stores of meal and flour, and washed away the newly
completed bridge. The town was cut off for six days.
1766. The loss of a safe crossing in 1621 contributed to a decline in the town's fortunes, and in 1766
Thomas, Earl of Kinnoull headed an effort to obtain funding for a new bridge. Financial backing from
the government and the Earl himself, as well as a public subscription led to the commission of
Smeaton’s Bridge which was completed five years later.
It was soon put to the test. In February 1774, during a rapid thaw, broken ice became wedged under
the bridge, and blocked up the river channel. Most of the town and both Inches were flooded, but the
bridge stood firm. Smeaton's bridge has survived many floods since. Some of the flood levels are
marked on the north side of the westmost pier.
Increasing traffic during the 19th century resulted in the bridge being widened by A. D. Stewart in
1869. The stone parapets were removed, and footpaths projected over iron brackets.
14 February 1774 The Tay had been frozen over in Perth for a month. When the thaw came, the ice
was raised by four feet and an eight mile continuous sheet of ice was released. As the ice broke up it
formed an ice dam at the three year old Smeaton’s Bridge, the water reached the top of the arches
and broke down the parapets but the new bridge held and the water level was marked on one of the
piers. There are now a number of such flood marks on the bridge pier giving a useful chronology of
subsequent flooding events.
February 1814 This flood led to the highest mark on the bridge again caused by flood following
freeze. Cannon were brought in to fire on the ice to break it up and the bridge shook from end to end
with the force of the water. (A more severe frost happened in 1838 with the river frozen over for two
months. Dinner parties on the ice were common, and even a civil banquet attended by 200 leading
citizens. However this time the thaw was gradual and there were no floods.)
7 October 1847 48 hours of heavy rain resulted in four foot deep floods in the centre of Perth.
Other floods occurred in 1849, 1851, 1853, 1868, 1894, 1903, 1909, 1910, 1912, 1913, and 1928.
15 June 1931 There was a midsummer flood which was unusual. The weather forecast had been for
dry and sunny weather but instead there was intense rain all day.
1947 Two hundred sheep were drowned on Moncrieffe Island when it flooded. Sheep have not
grazed there since. Other floods occurred in 1950, 1951, and 1974.
1985 Legislation was passed to enable people who are flooded or their insurers to take legal action
against planners or property developers to recover damages for negligent misrepresentation.
February 1990 Following a period of prolonged and heavy rainfall in the western and northern parts
of the catchment, a one in 20 year return period flow was recorded at Ballathie. Fortunately the peak
flow coincided with low tide. Following this flood, a report was commissioned on a new flood
prevention scheme. Before this resulted in any action, the 1993 flood occurred.
15 January 1993 This was a 100 year return period flood. During this event the highest ever
recorded flow on a UK river was recorded on the River Tay at the Ballathie gauging station. It was
2268 m3s-1, or nearly an Olympic sized swimming pool per second.1
Fortunately it was of fairly short duration and followed a period of heavy rain and snow with a sudden
rise in temperature. As in 1990, the peak flow coincided with low tide. Even so, 1,500 properties,
mainly in the city of Perth, were flooded. 1,200 of these properties were in the North Muirton council
housing estate. The full estate consists of 1,537 properties plus shops, schools and a pub. An
embankment had been built after the 1974 flood and it had survived the 1990 flood, but in 1993, the
flood embankment was overtopped and breached in three locations.
This was such an important event it is worth looking at in some detail.
Before the 1993 event
1
An Olympic sized swimming pool is 2,500 cubic metres.
2
In the days leading up to the event there was considerable snow fall in the River Tay catchment due
to the ‘Braer’ storm. Barometric pressure during this storm fell to 915 millibars in Shetland, a new UK
record. In Iceland, air pressure fell to 912 millibars, a European record and the equivalent of the eye
of a category 5 hurricane. Great foresight was shown in the form of the cooperation of the owners of
the large hydro electric schemes upstream of the Tay, as the reservoir water levels were allowed to
fall in order to provide capacity for the inevitable snowmelt, otherwise things could have been even
worse2. Just before the flood there was a sudden and extreme thaw, with temperatures rising by 15
degrees Celsius overnight.
The flood
On the morning of Friday, 15 January, flooding started to affect houses in Perth, and it was decided to
set up a relief centre at Perth Grammar School, which sits on slightly higher ground adjoining North
Muirton housing estate. The centre was in operation by 4pm, and continued operating throughout
Saturday, receiving a steady trickle of people who had been flooded. On Sunday, the scale of the
operation changed as predicted water levels reached danger point and warnings were issued to
householders. Elderly people in sheltered housing, nursing homes and hospitals were evacuated to
the Grammar school during Sunday morning and afternoon in a well organised procedure. The
Samaritans quickly deployed a full team at the school and they stayed on duty for 48 hours, talking
and listening to evacuees.
The water overtopped the flood banks in North Muirton at 4pm on the Sunday and started moving
towards the houses. By 7.30pm every street was filling with water and people started leaving their
homes. A steady stream started to arrive at the Grammar school, many on foot, some by car, and
some rescued by boat. The centre received 500 people that first night, but more arrived the next day.
The electricity and telephones in North Muirton failed around 10pm and those remaining in their
homes went upstairs and prepared for a long cold night. During the night, soldiers in boats visited the
houses still occupied and asked people if they wanted to leave. Many did, but some stayed until the
Monday morning. Over time, families were rehoused in temporary accommodation. The Council
bought a number of static caravans and took over a caravan site for evacuees. Of the 1,500 homes
flooded, 1,200 were in North Muirton, and of these, 873 were extensively damaged with floods up to
two metres deep after the embankment was breached. The council had insured the houses and were
able to recover the costs of repairs but some people did not return to their homes until October 1993.
Following the 1993 event
Insurers paid out over £100m in flood claims (at 1993 prices) after the Perth floods. Perth was the
first major flood in Scotland for many years, and attracted great sympathy and political support for
new defences. As a result, magnificent new flood defences costing £25m, including holding tanks
and pumps for surface water, were commissioned and completed in 2001. In addition, Perth Council
established Scotland’s first ‘Flood Appraisal Group’ involving local planners, property developers,
utilities, blue light services and a flood insurance expert. This set the pattern for a network of similar
groups across Scotland, and new planning policies made the establishment of such groups, renamed
“Flood Liaison and Advice Groups” compulsory for all local authorities. 28 out of the 32 Scottish local
authorities, covering 94% of the population established or joined such groups.
The Tay flood prevention scheme
This was designed to provide protection against a flood equivalent to 0.5m higher than the 1993
event. It was calculated that this would compensate for a 100 year return period extreme high tide
coinciding with a peak river flow of the order of the 1993 event. An assessment was also carried out
into the porosity of the soil and options to limit groundwater intrusion. The overall effect was a
scheme designed to protect against the 1993 and 1814 events combined with a 100 year extreme
high tide. New flood embankments to protect North Muirton would increase flows at the North Inch
which would provide flood storage. The total cost of the scheme was £26.5m. The 1993 floods cost
insurers over £100m, but for the purposes of a cost benefit analysis, HM Treasury approved tables
had to be used and they produced a flood loss of only £30m. Nevertheless, in Scotland, benefits only
have to exceed costs, so the scheme was eligible for grant aid. (In England and Wales, benefits have
to be at least six times costs to be eligible for grant aid.)
McInally, G A, Anderson, J L and Lee, D.,1995. “Positive operation of hydro-electric schemes to aid flood
control: experiences in the Tay catchment.” In: Reservoirs in River Basin Development. Eds – Santbergen & Van
Westen. Balkema, Rotterdam, The Netherlands.
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In recent years, Perth has won prestigious awards for the quality of its environment at regional,
national and international levels. It has been identified as having the highest quality of life in the UK.
Consequently there was concern about the visual impact of having a flood defence scheme through
the heart of the city. Archaeology was also an important issue. Perth is a historic settlement dating
back to the 12th century and was once the capital of Scotland. 2.3m high embankments on the North
Inch and 1.7m high walls along Tay Street had the potential to alter the character of the city.
Shallow slopes have been used on the embankments and they include a riverside path. Architectural
features have been incorporated in the Tay Street Wall, and it has all been clad in natural stone to
match the surrounding buildings. Mature trees were saved wherever possible and fresh ones planted.
Underground pumping stations throughout, are designed to remove surface water during flood events.
Stanners Islands
Stanners Islands represented an apparent constriction of the river flow area immediately downstream
of Smeaton’s Bridge. Historical records show that the islands had increased in size over the last
century. They are now covered in mature vegetation. It was calculated that 27,000 cubic metres of
material would need to be removed to increase the conveyance ability of the river, and this work was
seriously considered. (Scotland is the only country in Europe which could undertake such work
without contravening the Water Framework Directive.) In the end they have not been removed and
are still used by swimmers and wild life.
July 2002. In 2002, wet weather in the spring filled the holding tanks. Unfortunately, a severe
thunderstorm latched on to the town in July, and the ensuing cloudburst could not be contained.
Localised flooding ensued, exacerbated by the flood walls because the surface water pumps which
had been specified were not yet in operation. For the first time in its 100-year history, the two-day
Perth Agricultural Show had to be cancelled and the central park (called the ‘South Inch’) was closed
to visitors for the entire summer due to health fears from sewage.
July 2004. The Perth Show had a lucky escape in 2004, when just after it ended, torrential rain fell
for three days from a decaying hurricane, causing the cancellation of the Perth Highland Games for
the second time in three years. The surface water pumps were now operational so the flooding was
not severe. The floods of 1993, 2002 and 2004 were in line with climate change predictions: 1993
was a prolonged wet winter period with rapid thawing of snow. 2002 and 2004 were due to violent
summer thunderstorms. In the 2002 and 2004 floods, the public perhaps did not fully appreciate that
the parks used for the Agricultural Show and Highland Show were designated as sacrificial flood
storage as part of the flood prevention scheme. The cancellation of these two shows was a small
price to pay for saving widespread flooding of the homes and businesses in the city.
December 20063 The flood defences were tested again in December 2006. This followed a notable
wet period. The provisional rainfall figures for the UK indicate that December 2006 was the 4th
wettest since 1959 and the October to December period ranks the wettest in 50 years. The
November and December period rainfall was the highest for Scotland in a record dating back to 1914.
The December 2006 rainfall for the Tay catchment has been estimated to be around 177% of long
term average and for the November and December period 155% of long term average: equivalent to
an annual probability of around 25-33% (1:30 – 1:40). Flooding in Scotland was fairly widespread in
December 2006. During the flood event on 13th to 14th December SEPA recorded new maximum
peak flows on the River Tay at Pitnacree (792 m3s-1, 1 in 60 yr return period) where there is over 50
years of record and also on the River Lyon at Comrie Bridge upstream of Aberfeldy (509 m3s-1, 1 in
80 yr return period) and River Garry at Killiecrankie (669 m3s-1, 1 in 34 yr return period). Previous
maximum recorded flows at Pitnacree, Comrie Bridge and Killiecrankie were 732 m3s-1 (1993), 378
m3s-1 (1990) and 555 m3s-1 (1993) respectively. 1706 m3s-1 was recorded on the River Tay at
Ballathie. This flow has an annual probability of 5% (1 in 20 years). The flow was even more extreme
on the River Earn at 1 in 30 years. The flood defences operated perfectly to protect Perth.
Further reading
 “The Great Flood, A Chronicle of the events and people of Perth and Kinross during the flood
of January 1993” 112pp. Roger Smith, Perth and Kinross District Council, 1993.
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Source: Malcolm MacConnachie, SEPA Senior Hydrologist, 13 July 2007
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
“Perth Flood Defence Scheme”, Clive Bowman, Environment Services, Perth & Kinross
Council. Pp8-26. Journal of the Perthshire Society of Natural Science, Vol XVII, Perth,
2003.
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