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5. Physical Catchment Characteristics
5.1 Topographic Catchment Characteristics
The Argyll region has a particularly diverse topography, dominated by rugged glacial features
which have shaped the landscape into what we see today. Areas such as Kintyre provide areas
of low lying rolling hillsides suitable for intensive farming which are far removed from the rugged
mountainous terrain of South Argyll or Loch Linnhe. The island of Arran its self has been
described as a miniature Scotland due to its diverse range of both scabrous terrain in the north
of the island and low-lying flat ground in the south which is divided by the highland boundary
fault.
There are many differences between rivers that flow west through the Argyll district when
compared to those flowing east due to the more intensive glacial erosion. Westerly draining
rivers have a relatively short, steep course dominated by waterfalls large boulders and glacial
debris. In some cases rivers such as the Etive have long low gradient stretches in their upper
catchment flowing along upland moors before dropping steeply down to the valley floor through
steep bedrock gorges.
The steep rocky nature of Argyll’s rivers along with relatively high levels of precipitation lead to
there spate fed flow regimes which can rise to full spate and fall within 24 hours leading to a high
degree of substrate movement downstream. These substrates accumulate the lower reaches of
the rivers creating large alluvial deposits and gravel bars which in many cases are highly mobile
changing the course of the river from one year to the next.
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5.2 Geological Catchment Characteristics
5.2.1 Metamorphic Rocks
Metamorphic rocks are the result of the transformation of pre existing rocks. The pre existing
rocks or protolith can be made up of existing metamorphic, igneous or sedimentary rocks which
undergo a transformation under extreme heat and pressure. Metamorphic rocks make up a large
percentage of the earths crust and are classified by their chemical and mineral composition.
Metamorphic Rocks are formed in three ways firstly metamorphic rocks can be formed deep
beneath the earth’s crust where they are subject to extremes of temperature and pressure.
Metamorphic rocks are also formed by tectonic processes such as movement and collisions
between continental plates. Finally metamorphic rocks can also be formed when the rock is
heated by the intrusion of magma from beneath the earths crust.
5.2.2 Igneous Rocks
Igneous Rocks are formed by the cooling of magma either beneath the earths crust as intrusive
rocks or on the surface, extrusive. There are over 700 different recorded typed of igneous rocks
many of which can only be found beneath the earths crust.
5.2.2.A. Igneous Intrusive rocks
Igneous intrusive rocks are formed below the earth’s crust where the magma cools slowly and
solidifies surrounded by pre existing rocks. This slow cooling allows for a high degree of
crystallisation and forms rocks with a course grain which can be seen with the naked eye.
Igneous intrusive rocks are classified according to there shape, size of the intrusive body and its
relation to other rock formations into which it intrudes. Typical intrusive formations include
stacks, sills and dykes.
5.2.2.B. Igneous extrusive Rocks
Extrusive rocks are formed along the surface of the earths crust due to partial melting of rocks
within the earth’s mantle or crust. Magma is drawn to the surface because it is less dense than
the rock from which it was created. When it reaches the surface it is the liquid rock cools quickly
either in the air or beneath water leaving little time for crystallisation. In many cases a portion of
the extruded rock fails to crystallise atoll resulting in formations of natural glass.
5.2.3 Sedimentary Rocks
Sedimentary Rocks are formed from sediments which are deposited over time out of air, wind
water or ice. As sediment deposition builds up the increased pressure squeezes the sediment
into layers through a process known as lithification. The sediments build up over millions of
years and form distinctive layers known as strata.
Some sedimentary rocks can provide useful information about the earth’s history. Fossils of
animals and plants are common in sedimentary rocks as sedimentary rocks form at much lower
temperatures and pressures than other igneous and metamorphic rocks. The composition of the
sediments can provide useful information about changes to the environment throughout the
formation of the rock.
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5.2.4 Geological effects on water courses
The underlying bedrock can have a direct influence on the productivity of any watercourse which
runs over it. The process of rock weathering can be simplified into hard, slow weathering rocks
such as intrusive igneous rocks like granite or Rhyolite and softer sedimentary rocks which are
easily weathered such as Torridonian Sandstone or Limestone. Hard intrusive rocks such as
Granite weather extremely slowly at a rate of around 1 – 10 micro-meters every thousand years
and therefore release very few nutrients or minerals. Softer sedimentary rocks weather far
quicker.
Weathering rocks provide basic nutrients which all organisms rely on to survive, nutrients such
as calcium, magnesium, potassium, iron and phosphorus are released from rocks through the
weathering process and are not available through other processes. Hence rock weathering is in
many cases the limiting factor of the productivity of many watercourses
5.2.5 Catchment specific geological characteristics
5.2.5.A. Loch Linnhe and Firth of Lorne
The map showing Loch Linnhe and the Firth of Lorn details the bedrock types which are present
in this management area. The Loch Linnhe area is dominated by igneous extrusive rocks in the
form of undifferentiated basalt. In many areas intrusive rocks have formed dykes and sills. These
intrusions are split between basalt and dolerite intrusions in the south and Pozphyrite intrusions
in the north. Some sedimentary rocks are also present along the North West coast just south of
Oban where traces of old red sandstone can be found.
5.2.5.B. Lower Firth of Lorne
The Lower Firth of Lorne area is dominated by various types or metamorphic Rocks such as
slates, Phyllite, Epidiorite, conglomerates, quartzite grits and both hornblende and mica Schist’s.
Similarly to the Loch Linnhe area intrusions of basalt and dolerite are abundant across the area
and some smaller patches of limestone are also present.
5.2.5.C. Kintyre
The Kintyre management area is dominated by quartz-mica-schist on the eastern side separated
out by intrusions of basalt and dolerite. The western side of Kintyre is mainly Quartzose-micaschist on the western side separated from the east by two large seams which run along the
western side of the Kintyre peninsula one of limestone and another of Epidote-Chlorate-Schist.
Some small outcrops of old red sandstone can be found along the western coast with a large
section on the south east shore near Southend.
5.2.5.D. Loch Fyne
The Loch Fyne management area is dominated by metamorphic rocks such as slate, Mica
Schist and Phyllite on its northern banks with patches of intrusive Rhyolite, Trachyte and Felsite.
The southern coast of Loch Fyne is dominated by both Quartzose-Mica-Schist and Epidote-
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Chlorite-Schist small patches of quartzite grit are also present along with small limestone seams.
Basalt and Dolerite intrusions are also present across much of the catchment.
5.2.5.E. South Argyll
Similarly to the loch Fyne management area South Argyll is dominated by metamorphic rocks
with small patches of sedimentary rocks along the south coast. In many places igneous rocks
have formed complex networks of intrusions. The main metamorphic rock present is QuartzMica-Schist however slate and Mica-Schist are also present in the south. The southern coasts
contain patches of sedimentary rocks in the form of old red sandstone and limestone. Basalt and
Dolerite intrusions are present over much of the area with some Porphyrite and lamprophyre
intrusions are present in the east.
5.2.5.F. Island of Mull
The Island of Mull is Regarded as one of the most interesting geological areas throughout Britain
with geological features that can be found know where else in the world. Some of the oldest
rocks in the world can be found on mull including Lewissian Gneiss and Torridonian sandstone.
The north of the island is dominated by Basalt, Dolerite and Spilite however it is the igneous
complex in the southern end of the island which causes all the interest. A series of igneous
extrusions throughout mulls history formed a huge Plato which was thought to be around 6000ft
high which was then carved out by the effects of glacial erosion to leave the hard igneous
intrusive rocks below such as Gabbro, granite and Rhyolite.
5.2.5.G Islands of Islay and Jura
Islay and Jura are geologically very different Jura is dominated by metamorphic Quartzite grit. A
long seam of graphitic Schist and slate runs along the South Eastern coast while there are some
intrusions from igneous rocks throughout the island. In the south intrusions are dominated by
basalt and Dolerite while in the north there is a mix of Epidiorite and Hornblende Schist.
Islay in the other hand is significantly more complicated made up of a mixture of metamorphic
rocks with some sedimentary rocks located in the north west of the island. The sedimentary
rocks located in the north west of the island are made up of a mixture of sandstones and grit
with undifferentiated gneiss present to the south. Quartzite grit and slate are predominant across
much of the island with igneous intrusions of basalt, Anorthosite and Epidiorite across much of
the island. A few large limestone patches are also present across much of the north of the
island.
5.2.5.H Island of Arran
The island of Arran is one of the most complicated geological areas in Britain and is probably
one of the most visited by geologists. The geological features on Arran can be divided into two
main sections separated by the Highland Boundary Fault which curves round the large northern
granite intrusion between Lochranza and Dougarie. Igneous rocks such as granite and basaltic
lavas form around half of Arran’s bedrock. The large mass of granite located in the north of
Arran is thought to be the remnants of a large volcano which has eroded away leaving the
granite hills which remain today. The southern half of Arran is dominated by sedimentary rocks
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such as sandstones and mudstones. Intrusions of basalt and dolerite have created many of the
sills and dykes which can be seen today.
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5.2.6 Soil Types
The soil types also have a direct effect on any water course which passes over them both
directly influencing water retention and conductivity. The soil structure is an important part of
water regulation large particles such as pebbles and sand form a loosely bound free draining soil
which readily dries out during periods of drought. Smaller sub-microscopic clay particles bind
together forming soils which are impermeable and hold water. These particles together with
organic material also help determine the nutrient and mineral content of the soils.
5.2.6.A. Clay, silt and sand
Clay soils are chemically active and bind to particles of organic matter and water, when wet clay
solid become very wet and sticky. Due to the fine particles present in clay soils there are very
few air pockets clay is often impermeable to water and are prone to water logging and flooding.
Clay contains high nutrient levels but is much slower to erode and release these nutrients than
sandy soil types.
5.2.6.B. Sand
Sandy soils have a gritty texture formed from the weathering and erosion of rocks such as
limestone, sandstone, shale or granite. Sandy soils tend to be loosely bound together and are
prone to erosion from river banks. In addition to this sandy soils are well drained and have very
little capacity for water retention. The nutrient content of sandy soils is wholly dependent on the
amounts of organic material within the soil structure and nutrients which accumulate in sandy
soils are readily leached by heavy rainfall.
5.2.6.C. Diamiction
Diamiction is a geological term to describe soils composed of an unsorted mixture of sediments
where large sediments are set in a matrix of finer partials. Diamiction soil types are commonly
the result of glacial deposits which show significant lateral and vertical variations in thickness,
composition and texture.
5.2.6.D Peat
Peaty soils contain more organic material than most due to its acidity stopping complete
decomposition. Peat based soils are particularly good at holding water and the upland moors
and peat bogs provide good buffering capacity for spate and drought events. Due to the large
amounts of partly decomposed plant material few nutrients are released and rivers flowing off
peat soils are often nutrient poor.
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5.3 Land use
Land use can have profound impacts on aquatic organisms on adjacent watercourses the maps
overleaf describe the major land uses present throughout Argyll. The following maps have been
split into the relevant management areas and show the relative distribution of these major land
uses across each region.
5.3.1 Commercial forestry
Commercial forestry is one of the largest land uses in the Argyll area and provides huge
economic benefits to local communities. These large expanses of dense commercial forestry
shown in the following maps have posed significant problems for aquatic organisms.
Commercial forestry has been simplified for the purpose of this report and includes both newly
planted and recently felled forestry along with mature forests.
5.3.2 Mixed / Semi-Natural woodland
This section describes areas of mixed woodland, broadleaves, riparian woodland and seminatural woodland. This type of woodland is highly valuable from a biodiversity perspective as it
can support a huge array of species.
5.3.3 Improved Farmland
Argyll has some small patches of improved farmland which are sparsely distributed through out
the region. The section improved farmland covers any form of well maintained grazing pastures
and arable land. Arable farming is very localised to areas of low lying coastal areas or valley
floors and improved pastures for grazing make up most of this section. These improved pastures
are particularly important as they have high stocking densities and have a significant impact on
adjacent watercourses.
5.3.4 Rough Pasture and Upland Moor
Rough pasture and upland moor can be combined for the purpose of this description and make
up the second largest land use in the Argyll. These sections cover any area of rough pasture or
upland moor peat bog and heather moor in each case this land is used predominantly by
animals such as sheep and deer for grazing. In this case there is a moderate to light grazing
pressure depending on the quality or the land and the gradient.
5.3.5 Other
This section covers a number of different land uses such as tidal zones, salt marsh and sand
dunes. Also covered by this section are areas of mountain habitat and bracken. Any areas of
missing or obscured data has also been included.
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5.4 Summery of Climate Characteristics
This section provides general details of Scotland’s climate characteristics. The west of Scotland
results are applicable to the Argyll region. This data was provided by SNIFFER’s online
handbook of climate trends across Scotland.
5.4.1
Temperature
Table 1 – The changes in average temperature (in ºC) between 1914 and 2004 (left) and
between 1961and 2004 (right). Values in bold show that we are 95% confident (statistically) that
the change is part of a measurable trend.
North Scotland
1914 to 2004
East Scotland
West Scotland
Scotland
North Scotland
1961 to 2004
East Scotland
West Scotland
Scotland
Spring
0.59
0.83
0.66
0.69
1.03
1.23
1.20
1.14
Summer
0.50
0.59
0.43
0.51
1.06
1.12
1.08
1.08
Autumn
0.46
0.85
0.68
0.64
0.64
0.68
0.66
0.66
Winter
0.02
0.45
0.33
0.24
1.03
1.39
1.31
1.22
Annual
0.37
0.66
0.51
0.50
0.92
1.08
1.04
1.00*
For example, the figure at * in the table above means that using statistical analysis (see
Appendix 1) the average annual temperature increased by 1ºC between 1961 and 2004. This
figure is in bold because analysis indicates that we can be 95% confident that measurements
showed a genuine change over this time period. Similar analysis is used for each variable in
tables throughout the handbook.
Fig 1 - Changes in average temperature (in ºC) between 1961 to 2004 and 1914 to 2004.
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5.4.1.A. Regional trends in average temperature
There is a great deal of difference in the average annual temperatures between years for all
regions. The average annual temperatures in each region are now higher than at any other time
since 1914. The analysis from 1914 to 2004 shows a trend of increases in annual temperature,
particularly in East and West Scotland. This matches information about temperature increases in
the UK and around the world. Temperature increases have been greater since 1961 than
between 1914 and 1961. The increases in temperature we have seen since 1961 also are part
of a trend in each region and every season, apart from winter in North Scotland.
5.4.1.B. Spatial trends in average temperature
The increases are smallest during autumn and there has been some slight cooling in Highland
areas during autumn. The greatest increases have taken place during spring and winter and the
largest in southern and eastern Scotland in winter. The northern Outer Hebrides, Shetland and
Orkney are warming at a similar level in all seasons.
5.4.1.C. Future Trends in average temperature
Temperatures are expected to rise over Scotland, no matter which scenario of future emissions
is used, with increases being greatest during summer and autumn months (some models
suggest up to 4ºC) In line with the trends we have seen.
5.4.2 Average Rainfall
Average rainfall – Scotland over a whole year is on average 20% wetter than it was in 1961.
Winter precipitation shows a clear upward trend since this time, with a 58% increase recorded
across the country. This is most marked in the north (nearly 70% increases) and less marked in
the east (36% increase). There is less variability in precipitation across the other seasons and
patterns are less clear. The key trends for non winter months appear to be that the east has
become slightly drier during the summer and the west wetter in spring.
Table 2 - Changes in average precipitation totals (as a percentage), from 1961 to 2004 and
1914 to 2004. Values in bold show that we are 95% confident (statistically) that the change is
part of a measurable trend.
1914 to 2004
1961 to 2004
North Scotland East Scotland West Scotland Scotland North Scotland East Scotland West Scotland Scotland
Spring
13.9
6.1
22.0
14.3
16.2
9.4
17.3
14.8
Summer
-12.7
-18.9
-7.5
-12.7
-7.0
0.2
7.3
-0.6
Autumn
13.6
0.7
15.6
11.1
5.3
22.2
5.9
9.1
Winter
20.9
-0.8
9.0
11.6
68.9
36.5
61.3
58.3
Annual
9.6
-3.5
9.5
6.2
21.0
18.4
23.3
21.1
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Fig.2 - Changes in average precipitation totals (as a percentage), from 1961 to 2004 and 1914
to 2004.
5.4.2.A Regional trends in average precipitation
In each region, and across the country, the change in winter precipitation since 1961 shows a
clear upward trend. We can see an increase of almost 70% in winter precipitation in North
Scotland. The average precipitation each year also shows a trend towards much higher totals
over the same period. Scotland has become 20% wetter between 1961 and 2004.
But there has been little or no change in average summer precipitation totals in each region.
Changes in summer precipitation show no clear trend over the 1961 to 2004 period.
Looking at the 1914 to 2004 period, the pattern of change is less clear and we can see only two
trends - a reduction in summer precipitation in East Scotland and an increase in spring
precipitation in West Scotland.
The average precipitation each year has increased across most of Scotland since 1914, but
there has been a slight reduction in both average annual and winter precipitation in East
Scotland. This is the opposite of the trend measured over the period 1961 to 2004.
5.4.2.B. Spatial trends in average precipitation
The largest changes have taken place in winter months across all but the most eastern areas of
Scotland. In some areas of the west Highlands and the Hebrides, winter precipitation has more
than doubled since 1961.
The pattern of change is completely reversed in autumn, with eastern areas being the only
widespread region to become wetter, with increases of more than 20%.
In summer, northern areas of Scotland have become drier since 1961, particularly the northwest. This reduction in summer precipitation is more than 20% in some areas.
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5.4.2.C. Future trends in average precipitation
The UKCIP02 scenarios show relatively little change to average precipitation amounts each year
(the trend we have measured shows increasing totals) but winter months may become wetter
(as already seen) while summer months may be drier than at present (we have seen little
change so far).
The pattern of change may not be the same across Scotland. UKCIP02 estimate eastern
Scotland may experience the most extreme percentage changes in precipitation (going against
the trend we have seen already), with an increase in winter and a reduction in summer.
As with the trends of temperature change, there are similarities between the precipitation trends
over the longer 1914 to 2004 period and the expected changes in the future. Over the longer
period, the summer months have become drier and there has been relatively little change to the
average values each year.
5.4.3 Rainfall Intensity
Table 3 - Changes in average rainfall intensity on days with 1mm or more of rain (as a
percentage), from 1961 to 2004. Values in bold show that we are 95% confident (statistically)
that the change is part of a measurable trend.
Rainfall intensity (%)
North Scotland
East Scotland
West Scotland
Scotland
7.4
7.6
7.8
7.6
Figure 3 - Pattern of change (as a percentage) in rainfall intensity each year on days with 1mm
or more of rain, from 1961 to 2004.
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5.4.3.A. Regional trends in rainfall intensity
There is a trend of increasing rainfall intensity in both East and West Scotland. North Scotland
has a similar increase but this does not appear to be part of a trend, probably because natural
variability in rainfall is higher in this region. There does not appear to be a strong link between
year-to-year rainfall intensity over the three regions, although the long-term trend (smoothed
curve) is very similar.
5.4.3.B. Spatial trends in rainfall intensity
There is an increase for most of Scotland although there is a reduction for some northern and
coastal areas, including the Outer Hebrides, Orkney and Shetland Islands.
5.4.3.C. Future trends in rainfall intensity
It is very likely that the intensity of rainfall will increase in winter months. An east-west contrast in
change is estimated in the UKCIP02 scenarios, with the most extreme changes taking place in
eastern Scotland. This geographical contrast is clear in each of the UKCIP02 scenarios.
However, we have not seen this pattern when analysing the intensity of heavy rainfall we have
seen since 1961, although we cannot directly compare the measures we have used with those
used in the UKCIP02 report.
5.4.4 Other trends in Scotland’s climate
Growing Season – Since 1961, the growing season across the whole of Scotland has
lengthened by 33 days. This is particularly marked in coastal areas, in western Scotland where
the growing season is now nearly 37 days longer than in 1961 and the Shetland Islands where it
has been extended by over two months. The increase in growing season is most influenced by
an early start which on average now occurs 21 days earlier.
Frosts – Since 1961 there has been a 26% reduction in the number of days each year of air
frost. This reduction has been constant across the country, although some small areas in
northern Scotland have witnessed an increase. The reduction is most noticeable in the spring
and autumn seasons. Since 1961 there has been a 28% reduction in the number of days each
year of ground frost, although most of these reductions have occurred since the early 1980s.
Snow Cover – The number of days of snow cover has reduced across the country. This is
particularly prevalent in autumn where decreases of over 70% have been recorded (nearly 83%
in western Scotland).
Drought – There has been very little change in the maximum number of consecutive dry days
with little long term trends recorded since 1961. Overall there is a clear contrast in the number of
consecutive dry days between east and west Scotland, but there would appear to be no
significant changes since 1961.
Flooding – There is a clear trend of an increase in the levels of maximum five day precipitation
(i.e. maximum recorded precipitation over a five day period in any year) of about 20%. A steady
increase has been recorded across all Scotland. Increases in prolonged precipitation and rainfall
intensity may lead to greater flooding.
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The Marine Environment - The seas around Scotland have warmed by 1oC over the last 20
years. Warmer seas have prompted changes in composition, abundance and distribution of a
number of marine species including plankton, fish, sea birds, whales, mammals, dolphins and
porpoises.
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5.4.5 Rainfall Data from SEPA’s monitoring stations across Argyll
Table 4. List of SEPA's rainfall gauging stations and locations
Management Area
A1. Loch Linnhe
A2. Loch Linnhe
B. Lower Lorne
C1. Kintyre (West)
C2. Kintyre (East)
D. Loch Fyne
E. South Argyll
F. Mull
Name
Ganavan Bay
Glen Strae
Clachan Seil
Amod Farm
Dippin
Lingerton
Etterick bay
Tobermory
Easting
185700
215010
174700
164420
179800
186595
203180
149290
Northing
732420
729900
718285
612610
637760
685205
667105
754620
5.4.5 A1 Loch Linnhe - Ganavan Bay
Rainfall Data has been collected at Ganavan bay, Oban by The Scottish environmental
protection agency since 2003.
Mean Monthly Rainfall 2003 - 2006
Rainfall (mm)
250.0
200.0
150.0
100.0
50.0
0.0
jan
feb mar apr may jun
jul
aug sep oct
nov dec
Month
Fig 4. Mean monthly rainfall for Ganavan bay 2003 – 2006
The average monthly rainfall for Ganavan Bay, Oban shows clear trends in rainfall throughout
the year. The month with the highest rainfall was December 2006 with an average of 276.2mm
of rain falling in one month over 200mm greater than the lowest recorded rainfall of just 45.7mm
in January 2003. On average December and February are the wettest months with an average
rainfall of around 200mm and august the driest with an average of around 70mm.
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Total Annual Rainfall 2003 - 2006
Rainfall (mm)
2500.0
2000.0
1500.0
1000.0
500.0
0.0
2003
2004
2005
2006
Year
Fig 5. Total annual rainfall for Ganavan bay 2003 – 2006
2003 was the driest year with a difference of over 400mm between the next lowest year 2006.
The graph does show an overall increase in the total annual rainfall however due to the short
term nature of the data set it would be impossible to draw any overall conclusions as natural
fluctuations in rainfall occur regularly.
5.4.5 A2 Glen Strae
Rainfall Data has been collected at Glen Strae by The Scottish environmental protection agency
since 1997.
Year
Mean Monthly Rainfall 1997 - 2007
350.0
300.0
250.0
200.0
150.0
100.0
50.0
0.0
jan
feb mar apr may jun
jul
aug sep oct
nov dec
Month
Fig 6. Mean monthly rainfall from Glen Strae 1997 - 2007
The data collected by SEPA from Glen Strae shows a similar picture to that of Ganavan Bay.
Located around 30km west of Glen Strae, Gavavan Bay receives around half of the rainfall
which Glen Strae receives. This is most likely due to the topographical nature of both sites with
Glen Strae being located at the more mountainous North East end of Loch Awe and Ganavan
Bay being located on low lying coastal ground. The graph shows that February is the wettest
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
month with an average monthly rainfall of 330.1mm. In 2007 January was a particularly wet
month receiving the highest rainfall recorded in Glen Strae (572.2 mm).
Rainfall (mm)
Total Annual Rainfall 1997 - 2007
3500.0
3000.0
2500.0
2000.0
1500.0
1000.0
500.0
0.0
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Year
Fig 7. Total annual rainfall from Glen Strae 1997 - 2007
The data collected by SEPA shows the total annual rainfall for Glen Strae is increasing steadily
over the last 10 years with the highest recorded values occurring in 2005 (3104.2 mm) and 2007
(3038.0 mm). In both cases almost one third of the total annual rainfall fell in January and
February. As with many other areas in Argyll 2003 was a particularly dry year with 1910.5 mm
around 700mm less than the average annual rainfall. The average monthly rainfall for 2003
(159.2 mm) is over 50 mm less per month than the overall average (217.0 mm). The driest May
on record was also in 2003 with a monthly average of just 63.6 mm less than half the average
rainfall for May 132.0 mm.
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
5.4.5 B Lower Lorne - Clachan Seil
Rainfall Data has been collected at Clachan Seil, Lower Lorne by The Scottish Environmental
Protection Agency since 1996.
Rainfall (mm)
Ave rage M onthly Rainfall 1996 - 2006
180
160
140
120
100
80
60
40
20
0
Jan
Feb Mar
Apr May Jun
Jul
Aug Sep
Oct
Nov Dec
Month
Fig 8 - Average monthly rainfall for Clachan Seil 1996 – 2006
The data suggests that on average the months with the highest rainfall are November (169.0
mm) and December (151.6 mm). The month with the highest rainfall overall was November 2000
with an average of 269.4 mm of rain falling in one month over twice the monthly average of
123.0 mm. May (87.3 mm) and June (82.4 mm) are the driest months averaging around 40mm
less rain than the monthly average.
Total annual rainfall 1996 - 2006
Rainfall (mm)
2000
1500
1000
500
0
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Year
Fig 9 - Average Annual rainfall for Clachan Seil 1996 - 2006
The data collected by SEPA shows the total annual rainfall for Clachan Seil is increasing
steadily over the last 10 years with the highest recorded values occurring in 2005 (1713.6 mm)
and 2007 (1700.0 mm). this increase in rainfall suggested by the trend line is expected to be due
187
Argyll Fisheries Trust – 5. Physical Catchment Characteristics
to natural variation as years with a similar rainfall have been seen in 1998 (1664.0 mm). 2003
was a particularly dry year with 1085.4 mm around 400mm less than the average annual rainfall.
5.4.5 C1 West Kintyre - Amod Farm
Rainfall Data has been collected at Amod Farm by The Scottish environmental protection
agency since 1995.
Mean Monthly Rainfall 1995 - 2006
Rainfall (mm)
200
150
100
50
D
ec
N
ov
O
ct
S
ep
Ju
l
A
ug
Ju
n
M
ay
A
pr
M
ar
F
eb
Ja
n
0
Ye ar
Fig 10 - Average monthly rainfall for Amod Farm 1995 - 2006
The average monthly rainfall for Amod Farm suggests that there is a relatively long dry spell
throughout the summer months. May, June, July and August are the driest months however
average less than 30mm less than the total monthly average of 122.2 mm. the lowest recorded
rainfall occurred in august 2000 with an average of 28.4mm of rainfall. The months with the
highest rainfall are November (168 mm) and December (215 mm) significantly higher than the
average of 122.2 mm.
Total Annual Rainfall 1995 - 2006
1500
1000
500
20
04
20
05
20
06
20
01
20
02
20
03
19
98
19
99
20
00
0
19
95
19
96
19
97
Rainfall (mm)
2000
Ye ar
Fig 11 - Average Annual rainfall for Amod Farm 1995 - 2006
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
The data shows the total annual rainfall for Amod Farm is increasing steadily over the last 12
years. The irregular nature of this data set suggests that this is primarily due to natural variation
with the highest recorded values occurring in 1998 (1758.0 mm) and 2002 (1683.0 mm). This
particularly high figure of around 200 mm above the average annual rainfall in 1998 is due to
above average rainfall in seven months throughout the year. In November 1998 especially over
350 mm of rain was recorded around twice the average rainfall for that month. Figures of over
200 mm are relatively common with a monthly average of over 200 mm occurring once every
two years. 2003 was a particularly dry year with 1085.4 mm around 400 mm less than the
average annual rainfall.
5.4.5.C2 East Kintyre, Dippen
Rainfall Data has been collected at dippen by The Scottish environmental protection agency
since 1996.
Mean Monthly Rainfall 1996 - 2007
Rainfall (mm)
200
150
100
50
0
Jan Feb Mar Apr May
Jun
Jul
Aug Sep Oct Nov Dec
Month
Fig 12 - Average monthly rainfall for Dippen 1996 - 2007
The rainfall pattern for Dippen, East Kintyre is significantly different to that of South West
Kintyre. The long dry summer found at Amod Farm is significantly less noticeable with only May
and June receiving lass than 100mm of rain each month. When comparing to West Kintyre
Dippen receives around 200 m more rainfall annually than Amod Farm. The wettest months are
November (189.3 mm) and January (186.1 mm). In 2007 January was significantly wetter than
any other month with an average of 296.4 mm significantly higher than the average monthly
rainfall (142.0 mm) and higher than the average for that month (186.1 mm).
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
Total Annual Rainfall 1996 - 2007
Rainfall (mm)
2500.0
2000.0
1500.0
1000.0
500.0
20
06
20
07
20
03
20
04
20
05
20
01
20
02
19
98
19
99
20
00
19
96
19
97
0.0
Year
Fig 13 - Total Annual rainfall for Dippen 1996 - 2007
The total annual rainfall for Dippen decreased steadily over the last 12 years. The irregular and
short term nature of this data set suggests that this is primarily due to natural variation with the
highest recorded values occurring in 1996 (2319.5 mm). This particularly high figure of around
600 mm above the average annual rainfall is due to abnormally high rainfall in August and
September 1996. 2006 was a particularly dry year with 1293.6 mm around 500mm less than the
average annual rainfall. In particular January, February and March received less than average
rainfall as did November and December these months are particularly key with regard to
migratory fish movement and may have caused significant problems to fish making there way to
and from spawning grounds.
5.4.5 D Loch Fyne - Lingerton
Rainfall Data has been collected at Lingerton, Loch Fyne by The Scottish Environmental
Protection Agency since 2005.
Mean Monthly Rainfall 2005 - 2007
250.0
Rainfall
200.0
150.0
100.0
50.0
0.0
jan
feb mar apr may jun
jul
aug sep oct
nov dec
Month
Fig 14 - Average Monthly rainfall for Lingerton 2005 - 2007
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
The data collected form Lingerton is different to that of other sites in Argyll. The data set appears
to be more irregular with little correlation between summer and winter months. This is likely to be
caused by the extremely short data set. One similarity is that the wettest months are November
(193.2 mm) and January (188.0 mm). July is the driest month overall with an average rainfall of
(49.4 mm) around half the average monthly rainfall (133.7 mm). February is also a particularly
dry month according to the data with an average rainfall of (87.8 mm).
Total Annual Rainfall 2005 - 2007
Rainfall (mm)
1900.0
1800.0
1700.0
1600.0
1500.0
1400.0
1300.0
2005
2006
2007
Year
Fig 15 - Total Annual rainfall for Lingerton 2005 - 2007
The average rainfall recorded at SEPS’s rainfall gauging station 1603.8 mm appears to be
relatively similar to other coastal sites such as Ganavan Bay or Clachan Seil. 2006 was
significantly wetter than the other years for which data has been collected with a total rainfall of
1786.2 mm, over 200 mm more than either of the other years.
5.4.5 E South Argyll - Ettrick Bay
Mean Monthly Rainfall 2002 - 2007
Rainfall (mm)
200.0
150.0
100.0
50.0
0.0
jan
feb mar apr may jun
jul
aug sep oct
nov dec
Month
Fig 16 - Average Monthly rainfall for Eterick Bay 2002 - 2007
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
The rainfall data collected by SEPA for Etterick Bay, Bute shows a relatively stable rainfall
pattern for most of the year between March and October averaging 98.3 mm for these months
with slightly dryer spells in May (82.5 mm) and August (76.5 mm). The wettest months are
February (169.6 mm) and December (149.2 mm). In 2002 March was significantly wetter than
any other month with an average of 257.6 mm significantly higher than the average monthly
rainfall (113.8 mm) and substantially higher than the average for that month (104.6 mm).
Total Annual Rainfall 2002 - 2007
Rainfall (mm)
2000.0
1500.0
1000.0
500.0
0.0
2002
2003
2004
2005
2006
2007
Year
Fig 18 - Total Annual rainfall for Eterick Bay 2002 - 2007
The total annual rainfall has remained relatively stable throughout the sample period with the
exception of 2003 (1034.0 mm). 2002 had the highest annual rainfall recorded at Etterick Bay
1540.2 mm. One interesting point is that the last three years have been remarkably similar in
Etterick Bay with a difference of around 50 mm between these years. In comparison to other
areas in Argyll such as Lingerton when differences of up to 200 mm have been recorded
between these three years.
5.4.5 F Mull - Tobermory
Mean Monthly Rainfall
Rainfall (mm)
250.0
200.0
150.0
100.0
50.0
0.0
jan
feb mar apr may jun
jul
aug sep oct
nov dec
Month
Fig 19 - Average Monthly rainfall for Tobermory 2002 - 2007
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
The rainfall data collected by SEPA for Tobermory, Mull shows the wettest months to be
December (201.1 mm) and January (200.3 mm) significantly more than the average monthly
rainfall for Tobermory (152.8 mm). The driest month overall, August (97.7 mm) was notably
dryer in both 2005 (71.0 mm) and 2007 (91.4 mm). The highest rainfall recorded at Tobermory
was recorded in January 2007 with a total of 326.4 mm around 120 mm more than the average
January rainfall 200.3 mm.
Total Annual Rainfall 2002 - 2007
Rainfall (mm)
2500.0
2000.0
1500.0
1000.0
500.0
0.0
2002
2003
2004
2005
2006
2007
Year
Fig 20 - Total Annual rainfall for Tobermory 2002 - 2007
The total annual rainfall data from Tobermory suggests that there has been a significant
increase in rainfall over the last 6 years however this is due to natural variation in rainfall
patterns. As with most of the Argyll region 2003 was a particularly dry year with an annual
rainfall of 1356.4 mm around 500 mm less than the average annual rainfall (1833.1 m)
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
5.5 River Flow Characteristics
5.5.1 Loch Linnhe – River Awe catchment
The Awe system is located in Northern Argyll on the west coast of Scotland. The River Awe
drains out of the North Western arm of Loch Awe, flowing into Loch Etive, a sea loch connected
via the falls of Lora to Loch Linnhe. The whole catchment has an area of 780 sq. km and a
mean altitude of 307m. The catchment includes 157 lochs and a network of 1249 stream
junctions. Loch Awe, at 41 km long, is the longest in Great Britain with a relatively narrow
breadth of less than 1 km. The total surface area is 38.5 sq. km, the third largest in Great Britain,
a mean depth of 32m and a water retention time of 0.72 years (263 days).
The Scottish environmental protection agency has seven gauging stations located on several
rivers across the Loch Awe catchment (see fig 1) and additional information has been gathered
by Scottish and Southern Energy for the River Awe. Only two gauging stations will be used in
this report the River Orchy gauging station in Glen Orchy and data provided by S&SE from the
River Awe barrage. The River Orchy is the largest tributary in the Loch Awe system and drains
the headwaters of Loch Tulla, Allt Kinglass, Lochy and Strae Rivers before flowing into the
Northern end of Loch Awe.
5.5.1.A1 River Orchy
I. Annual flow
35.000
Flow (Cummecs)
30.000
25.000
20.000
15.000
10.000
5.000
0.000
1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006
Fig 1. Total Annual Flows for the River Orchy 1979 - 2006
The graph above fig 1 shows the total annual flows from the River Orchy. The River Orchy has
an Annual flow of just over 20,000 cumecs. The trend line shown in Fig 1 suggests that the total
flow is increasing throughout the sampling period however this is most likely due to natural
variation between rainfall patterns. The data suggests that 1988 was one of the worst years in
terms of total flow with the average flow reaching nearly 30,000 cumecs. The lowest flow
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
recorded during the sampling period was in 1991 (2516 cumecs) around 5000 cumecs less than
the average flows and over 8000 cumecs less than the highest peak.
Flow (cumecs)
II. Weekly flow
45.00
40.00
35.00
30.00
25.00
20.00
15.00
10.00
5.00
0.00
Week Week Week Week Week Week Week Week Week Week Week Week Week
1
5
9
13
17
21
25
29
33
37
41
45
49
Fig 2 Mean Weekly Flows for the River Orchy 1979 - 2006
Fig 2 shows the mean weekly flows for the River Orchy between 1979 and 2006. The red trend
line indicates the mean weekly flow throughout the sampling period (28.89 cumecs) and the blue
trend line indicates the mean weekly summer and winter flows (11.24 and 30.02 cumecs) The
periods of highest flows are during the start of the year during January to March and again at the
end of the year September through to December. Week 1 has the highest average flow recorded
throughout the sampling period (38.23 cumecs). The lowest recorded flow was in week 25 (9.51
cumecs).
!!!. Spate data
140
100
80
60
40
20
05
20
03
20
01
20
99
19
97
19
95
19
93
19
91
19
89
19
87
19
85
19
83
19
81
19
79
0
19
No. of Spate Days
120
Fig 3. Total Number of Spate Days Each Year 1979 - 2006
195
Argyll Fisheries Trust – 5. Physical Catchment Characteristics
Fig 3 indicates the total number of days per year that the river Orchy was in spate. The graph
shows that on average the number of days when the River Orchy was in spate has increased
throughout the sampling period. This confirms the data shown in figure 1 showing an increase in
the annual flows. The data shows that the year with the highest number of spate days was 1986
with a total of 129 days when the river was at an above average level. It would be expected that
the years with the highest number of spate days would correlate with the years with the highest
total rainfall however this is not the case here.
No. of Spate Days
30
25
20
15
10
5
0
>20
>30
>40
>50
>60
>70
>80
>90
>100
Size of Flow (cumecs)
Fig 4. Average No. of Spate Days with relation to Flow Size 1979 - 2006
Fig 4 shows the mean number of spates days per year to have taken place within the sampling
period 1979 – 2006 with relation to Spate size. The graph shows that spates of 150 cumecs are
relatively common and occur regularly throughout a year, these large spates are likely to
mobilise substrates and cause increased erosion. Prolonged spates of this size can cause more
serious damage due to increased rates erosion. In 1983 there was a prolonged spate which
peaked twice at around 200 cumecs; this spate event lasted for around 20 days before
dissipating. Larger spates of 300 or 400 cumecs are less frequent with only 10 spate days of
300 cumecs occurring throughout the 20 year sampling period. The only spates recorded which
were over 400 cumecs were recorded in 1979 (413.2 cumecs) and 1998 (445.31 cumecs). The
largest recorded spate was on the 14th of December 2006 and measured 447.75 cumecs see
pictures overleaf.
Note:
The increase in the number of large spates shown on figure 4 is due to the >100 section taking
into account all spate events over this size including the 400 cumec spate events mentioned
above.
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
The River Orchy taken on the 14th of December 2006.
Bridge of Orchy.
Lower Catnish
Lower Glen Orchy
Ladies Pool Black mount.
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
IV. Low Flow Data
Periods of below average flows can have profound effects on aquatic organisms. The reduced
wetted area can cause increased competition for food and resources for many species. Figure 5
below shows the mean number of days per year with a below average flow from 1979 – 2006.
the trend line shown on Figure 5 suggests that there has been a significant increase in the
number of dry days recorded in the river Orchy throughout the sample period. This increase in
dry days throughout the sample period together with the increase in the number of spate days
shown in figure 3 suggests that there is a significant increase in rainfall intensity.
350
Number of Days
300
250
200
150
100
50
19
79
19
81
19
83
19
85
19
87
19
89
19
91
19
93
19
95
19
97
19
99
20
01
20
03
20
05
0
No. of Days
Fig 5. Total No. of Days With Below Average Flow 1979 – 2006
90
80
70
60
50
40
30
20
10
0
<10
<5
<2
<1
<0.5
Size of Flow (Cumecs)
Fig 6. Mean No. of Days with Below Average Flows with Relation to Flow Size 1979 – 2006
Flows of under 10 cumecs are mean summer flow for the River Orchy even lower flows such as
2 or less cumecs could have a significant effect on fresh water ecosystems if this low flow was to
be prolonged. Fig 6 shows the average number of days per year where the flow is less than half
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
the average flow. On average low flows of less than 1 cumec are recorded on around 8 days a
year however throughout the sample period flows of 0.5 cumecs or less have been recorded.
Flows of 0.5 cumecs have been recorded on a total of 19 days between 1982, 1984 and 2001.
5.5.1.A2 River Awe
The major feature of the Awe catchment is the Awe Hydro Electric Scheme which consists of a
dam, the barrage built in 1963, at the western end of the Pass of Brander. The barrage is used
to control the height of the water in Loch Awe and the flow exiting the loch into the River Awe.
The barrage allows upstream fish passage via a boreland lift constructed within the barrage
structure. The presence of a fish counter at the exit point of the pass allows a daily count of fish
movement to be made.
I. Weekly Level
33.00
Height (m eters)
32.50
32.00
31.50
31.00
week51
week49
week47
week45
week43
week41
week39
week37
week35
week33
week31
week29
week27
week25
week23
week21
week19
week17
week15
week13
week11
week9
week7
week5
week3
30.00
week1
30.50
Fig 7. Mean Height of the River Awe 2006 – 2007
the graph above Figure 7 shows the Mean weekly height of the river awe in meters. Due to the
presence of the dam the water level in the river awe easily regulated buffering of any spate or
drought events. The blue trend line indicates the average height of the river awe throughout the
year(31.29 meters). The red trend line shows the minimum compensation flows throughout the
year.
Note:
Weeks 29 – 31 show flows which are under the minimum compensation flows. this was due to
water being released through radial gates which interrupts the way in which the water level is
monitored.
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5.5 2 East Kintyre – River Carradale
The Carradale Water is a relatively large catchment of 58.6km2 (13th largest in the Argyll region)
situated on the eastern side of the kintyre peninsula, Argyll. The Carradale is a spate fed river
which flows from north to south from the high ground of cnoc nan Craobh (322m) and cruach
Mhic-an t-Saoir (364m) in the north west and Beinn Bhreac (244m) in the north east. The
Carradale is bordered by the catchments of the ballochroy and crossaig burns to the north, the
kilean burn and the Clachaig water to the west and the Barr water to the south. The main river
covers some 12 km before flowing into the kilbrannan sound near the settlement of Carradale.
I. Total Flow
900
Total Flow (Cumecs)
800
700
600
500
400
300
200
100
20
01
20
02
20
03
20
04
20
05
20
06
19
96
19
97
19
98
19
99
20
00
0
Fig 8. Total Mean Flow for the River Carradale 1996 - 2006
the graph above figure 8 shows the total mean flow from the River Carradale at Dippen from
1996 – 2006. the mean flow for the river Carradale is around 700 cumecs however there is a
high degree of fluctuation from year to year. The trend line shown on figure 8 suggests that the
total annual flow has decreased throughout the sample period. This decrease in total annual
rainfall is likely to be due to natural variation in rainfall patterns when considering the short term
nature of the data set and highly fluctuating results. The highest recorded annual flow was in
1998 (872.7 cumecs) nearly 200 cumecs above average and nearly 100 cumecs over the next
highest year in 2000. the lowest flows (547.4 cumecs) was recorded in 2003 again around 200
cumecs below the average flows.
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
II. Weekly Flow
4.00
M ean F lo w (Cu m ecs)
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
Week Week Week Week Week Week Week Week Week Week Week Week Week Week Week Week Week Week
1
4
7
10
13
16
19
22
25
28
31
34
37
40
43
46
49
52
Fig 8. Mean Weekly Flow for the River Carradale 1996 - 2006
The graph above details the mean weekly flows for the river Carradale between 1996 – 2006.
the red trend line shows the average weekly flow throughout the sampling period (1.86 cumecs)
and the blue trend line shows the summer and winter averages 1.18 cumecs and 2.54 cumecs
respectively. The highest peak on average is in week 48 with a weekly flow of 3.74 cumecs.
Some particularly low flows are present through the summer particularly between week 26 and
29 with flows below one cumecs being recorded frequently.
III. Spate Data
160
140
No. of Days
120
100
80
60
40
20
0
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Fig 9. Total No. of Spate Days Per Year 1996 - 2006
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
Figure 9 shows the total number of days per year when the River Carradale was in spate. On
average the River Carradale has a higher than average flow for 112.91 days however the trend
line suggests that there has been a decrease in the number of days with a higher than average
flow. This decrease in the number of spate days of around 1 day per year could have a profound
impact on migratory fish populations.
40
No. of Days
35
30
25
20
15
10
5
0
>2
>3
>4
>5
>6
>7
>8
>9
Size of Flow (Cumecs)
Fig 10. Average No. of Spate Days with relation to Flow size 1996 - 2006
Fig 10 shows the average number of spates days to have taken place within the sampling period
1996 – 2006 with relation to Spate size. The graph shows that spates greater than 2 cumecs are
relatively common and occur regularly throughout a year. Larger spate events of greater than 5
or 8 cumecs occur less frequently. Spates measuring 8 cumecs or more occur on average for 5
days a year.
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
IV. Low Flow Data
160
140
No. of Days
120
100
80
60
40
20
0
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Fig 11. Total No. of Days with Below Average Flow 1996 - 2006
Figure 11 above describes the number of days annually with a below average flow between
1996 and 2006, the trend line shows an increase in the number of days with a below average
flow of around 1 day per year. This increase in the number of dry days could have a profound
effect on fish populations both effecting the migration of fish species and causing increased
competition with a reduced wetted area.
The results shown between the spate and low flow data support the results shown in figure 8
suggesting that the annual rain fall is decreasing.
250
No. of Days
200
150
100
50
0
<1.75
<1.5
<1.25
<1.00
<0.75
<0.5
<0.25
<0.1
Size of Flow (cumecs)
Fig 12. Mean No. of Days with Below Average Flows in relation to Flow Size 1996 - 2006
The River Carradale has over 200 days a year with a below average flow however it is only the
particularly dry days which will cause a problem for fish populations. Flows of under 0.5cumec
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
are common throughout the year occurring on around 100 days. The average summer flows
described in Fig 8 suggests that flows of 0.5 cumecs are less than half the average summer
flow. Flows of around 0.5 cumecs occur on average twice a year however flows of 0.05 have
also been recorded and occur every two to three years.
5.5.3. South Argyll – Delongart
I. Total Flow
Total Flow (cumecs)
1200.00
1000.00
800.00
600.00
400.00
200.00
0.00
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006
Fig 13. Total Annual Flow for the Little Eachaig River 1980 - 2006
Figure 13. Describes the total annual flow for the Little Eachaig River in south Argyll between
1980 – 2006. the average flow for the little Eachaig is around 669 cumecs however As with
other areas there is a high degree of fluctuation from year to year. The trend line shown on fig
13 suggests that the total annual flow has increased throughout the sample period however this
is likely to be due to natural variation in rainfall patterns. The highest recorded annual flow was
in 1999 (975.6 cumecs) over 300 cumecs above average and over 100 cumecs over the next
highest year in 1998. the lowest flows (471.1 cumecs) was recorded in 2001 around 200 cumecs
below the average flows. It is evident from this graph that the fluctuations between dry and wet
years is becoming more severe with both the highest and lowest flows recorded occurring within
the last few years.
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Argyll Fisheries Trust – 5. Physical Catchment Characteristics
II. Weekly Data
Average Flow (cumecs)
4.000
3.500
3.000
2.500
2.000
1.500
1.000
0.500
week 51
week 49
week 47
week 45
week 43
week 41
week 39
week 37
week 35
week 33
week 31
week 29
week 27
week 25
week 23
week 21
week 19
week 17
week 15
week 13
week 11
week 9
week 7
week 5
week 3
week 1
0.000
Fig 14. Mean Weekly Flows for the Little Eachaig River 1980 - 2006
Fig 14 shows the mean weekly flows for the Little Eachaig between 1980 and 2006. The red line
indicates the average weekly flow throughout the sampling period (1.91 cumecs) and the blue
line indicates the average weekly summer and winter flows (1.13 and 2.58 cumecs) The periods
of highest flows are during the start of the year during January and again at the end of the year
September through to December. Week 1 has the highest average flow recorded throughout the
sampling period (3.78 cumecs). The lowest recorded flow was in week 29 (0.78 cumecs).
III. Spate Data
Similarly to the total annual flows shown in Fig 13 the number of days per year with an above
average flow shown below Fig 15 suggests a high degree of variation between years of high or
low flows. As expected the year with the highest and lowest numbers of spate days corresponds
to that of figure 13 1999 and 2001 respectively.
160
140
100
80
60
40
20
0
19
79
19
81
19
83
19
85
19
87
19
89
19
91
19
93
19
95
19
97
19
99
20
01
20
03
20
05
No. of Days
120
Fig 15. No. of days with above average flow 1979 - 2006
205
Argyll Fisheries Trust – 5. Physical Catchment Characteristics
The largest recorded spate was recorded in the Little Eachaig River (25.906 cumecs) was
recorded on the 29th of October 1998. This peak was remarkably sudden jumping from around 2
cumecs to 25 in the pace of 24 hours. This spate event dissipated relatively quickly with the river
returning to normal flows within four or so days.
70
No. of Days
60
50
40
30
20
10
0
>2
>5
>10
>15
Flow Size (cumecs)
Fig 16. Mean No. of Spate Days with relation to Flow size 1979 - 2006
Fig 16 shows the mean number of spates days per year to have taken place within the sampling
period 1979 – 2006 with relation to Spate size. The graph shows that spates greater than 2
cumecs are relatively common and occur regularly throughout a year. Larger spate events of
greater than 10 or 15 cumecs occur less frequently. Spates measuring 10 cumecs or more occur
on average for 6.18 days a year with larger spates of 15 cumecs or more occurring on average
for 1.21 days a year. In 1999 there was a prolonged spate which peaked three times at 15
cumecs; this spate event lasted for around 10 days before dissipating.
IV. Low Flow Data
350
No. of Days
300
250
200
150
100
50
19
78
19
80
19
82
19
84
19
86
19
88
19
90
19
92
19
94
19
96
19
98
20
00
20
02
20
04
20
06
0
Fig 17. Total No. of Days with a Below Average Flow 1978 - 2006
206
Argyll Fisheries Trust – 5. Physical Catchment Characteristics
The low flow data provided by SEPA for the Little Eachaig River suggests a relatively stable
number of low flow days occurring throughout the sample period. The Little Eachaig river has an
average of 250 days with a below average flow around 100 days more than the River Carradale
in East Kintyre. In 1980 there was 318 days with a flow which was equal to or below mean
values.
The Graph below (fig 18) describes the relative size of the low flow events recorded throughout
the sample period. The other graphs of this type constructed from data from either the River
Orchy or Carradale show a distinct exponential reduction in the number of days with regard to
flow size which is not shown here. There could be many reasons for this anomaly which would
require further investigation to fully explain.
70
No. of Days
60
50
40
30
20
10
0
<1
<0.75
<0.50
<0.25
Size of Flow (cumecs)
<0.1
Fig 18 Mean No. of Days with Below Average Flows with Relation to Flow Size 1979 – 2006
207
Argyll Fisheries Trust – 5. Physical Catchment Characteristics
5.4.4 Arran – Machrie Water
Total Flow (cumecs)
I. Total Flow
500
450
400
350
300
250
200
150
100
50
0
2003
2004
2005
2006
Fig 19 Total Annual flow for the Machrie Water 2003 - 2006
Due to the lack of information from this gauging station it would be impossible to draw any strong
conclusions from the data set. The graph shows a steep increase in the total annual flow
between 2003 and 2006. it is likely that this steep increase is due to natural variation in rainfall
patterns rather than a direct increase in rainfall over such a short time.
II. Weekly Flow
3
2.5
2
1.5
1
0.5
W
ee
W k1
ee
W k3
ee
W k5
ee
W k7
e
W ek 9
ee
W k 11
ee
W k1
ee 3
W k1
ee 5
W k1
ee 7
W k 19
ee
W k2
ee 1
W k2
ee 3
W k 25
ee
W k2
ee 7
W k2
ee 9
W k3
ee 1
W k 33
ee
W k3
ee 5
W k3
ee 7
W k3
ee 9
W k 41
ee
W k4
ee 3
W k4
ee 5
W k4
ee 7
W k 49
ee
W k5
ee 1
k5
3
0
Fig 20 Average Weekly Flows for the Machrie Water 2003 – 2006
The graph, shown above details the mean weekly flows on the Machrie water throughout the
sampling period. The particularly erratic nature of this data set is primarily due to the short term
208
Argyll Fisheries Trust – 5. Physical Catchment Characteristics
data set. Over a period of years the data would buffer any anomalies and show a more stable
picture of weekly river flows.
209