Fearn Wind Energy Project

Geology, Superficial Deposits and Hydrology

Orkney Sustainable Energy Report OSE/2871 Geology Orkney Sustainable Energy Document OSE/2871 Geology March 2010

Report OSE/2871: Section 6 March 2010

Client: David Sutherland Tullich Farm Fearn

Assessment:

Richard Gauld IEng MInstMC BSc(Hons) Dip.GeoSci Dip.DesInn

Orkney Sustainable Energy Ltd 6 North End Road Stromness Orkney KW16 3AG

CONTENTS

1 SUMMARY 3

2 LANDSCAPE AND GEOMORPHOLOGY 4

3 GENERAL GEOLOGY 5

4 SUPERFICIAL DEPOSITS 6

5 HYDROLOGY AND HYDROGEOLOGICAL FEATURES 7

6 ICE AND SNOW EFFECTS 8

7 HYDROLOGICAL MANAGEMENT AND POLLUTION PREVENTION 9

REFERENCES AND BIBLIOGRAPHY 10

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1 Summary

1.1 A wind energy project is proposed for a derelict aerodrome on the Tarbat Peninsula, east of Tain in Easter Ross. The project consists of three large scale wind turbines, an upgraded access and a switchgear building, all to be owned by a local company. As part of the planning process, studies relating to the possible effects of the wind turbine development on the geology, superficial deposits, hydrogeology and hydrology beneath and across the site have been undertaken.

1.2 The site has been surveyed over four years as part of the project ecological assessment, with any hydrological features noted and mapped. The project layout has evolved over the assessment period, and as the project has been designed to have minimum ecological impact, care has been taken to avoid areas of sensitive habitats. In addition, a walkover survey was completed, identifying any surface water features, including sources, drains and burns. The project has taken into account ground conditions, and has located the turbines on or adjacent to the derelict runways of the aerodrome; particular care has been taken to avoid areas of natural vegetation or bog.

1.3 This is a geologically interesting area, and the large flat plain around Fearn Aerodrome is the consequence of post-glacial isostatic uplift and relative sea level fall. The underlying bedrock is the Raddery Sandstone Formation, a pebbly red sandstone of Mid Devonian age. The main superficial deposits are gravel shingle, sand and silt forming a raised marine deposit that stretches from Nigg in the south to Cadboll in the east, dated from the current Holocene interglacial. These are very young deposits, and represent the sea bed during the warm period immediately after the Scottish ice sheets retreated, between 6,000 and 10,000 years ago. The extent of these raised marine deposits suggests that the Cromarty Firth had outfalls near Cadboll and Loch Eye. Isostatic effects and relative sea level fall over the last 5,000 years have raised the land, creating the flat plain extending from the intertidal zone at Nigg to Fearn. Without anthropogenic influences this would be a marshy area, but has seen extensive drainage to establish the fields around the aerodrome.

1.4 Assessment of the risk of possible ice and snow effects has been completed, with a low probability of icing, and in any event the turbine site is well away from housing, public roads and powerlines. Consequently ice throw is not predicted to be a significant issue for the Fearn Wind Energy Project.

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2 Landscape and Geomorphology

2.1 The project is located on Tarbat Peninsula, a largely flat plain extending from Nigg in the south, to Portmahomack in the north and Balintore in the east. Nigg Hill is locally prominent, providing a backdrop to the well managed agricultural fields. To the south of Nigg Hill are the Sutors of Cromarty, two prominent headlands that define the entrance to the Cromarty Firth. The turbine site is the Fearn Aerodrome, a derelict Royal Navy air base, known as HMS Owl, with the turbines located on or adjacent to the disused runaways. Access to the site follows an existing track off the B9166 that runs between Hill of Fearn and Balintore, with a switchgear house located on the site. The project connects to the National Grid at a substation near the A9, Figure 1.

2.2 The general area is defined as Open Farmed Slopes in the Inner Moray Firth Landscape Character Assessment (SNH 1998), and consists of a largely flat plain gradually rising from Nigg Bay to Tarbat Ness. This landscape type is characterised by extensive drainage and land reclamation resulting in a strong geometric pattern of small and moderate scale fields, giving a diverse but well-ordered landscape. The location of the project could also be considered to be an area of Intensive Farming, similar to the landscape between Hill of Fearn and Tain, but in any event is a brown-field development site that requires significant renovation.

2.3 The geomorphology of the site has been largely controlled by the underlying geology. The bedrock is made up of hard sandstone sediments, which have been cut by glaciers to create a fjord-type river estuary. Throughout this area, the routes of glaciers, sea level changes, along with significant glacial sand and gravel deposits have created a series of large open firths. On the Fearn site itself, marine deposits cover much of the area, draping the bedrock with varying depths of gravel single, sand and silt due to falls in relative sea level from climatic changes and isostatic effects.

2.4 Anthropogenic influences in recent years have significantly altered the landscape. The intertidal zone around Nigg Bay and the boggy floor of the north shore of the Cromarty Firth around Tarbat and Fearn have been subject to drainage and land reclaimage, eliminating the need to move cattle to high ground during the summer months. As a result the character of the area has changed, with older traditional landuse disappearing, replaced by a more regular pattern of arable and improved grasslands, and the creation of large farmhouses surrounded by meadows.

4 Orkney Sustainable Energy Document OSE/2871 Geology March 2010 3 General Geology

3.1 This is a relatively homogenous area from a geological perspective, dominated by sedimentary bedrock that was originally an area of sand and mud deposited in the Mid Devonian period, around 390M years ago. The great glacial events over the last 2M years have worked this coastline, creating the varied coastal forms, cliffs, bays, firths and estuaries. The Great Glen fault extends northwards to the east of the Cromarty Firth, with Nigg Hill and Tarbat Ness defining the western side of the fault; the Great Glen is a major strike/slip fault that defines the boundary between the older Northern Highlands to the west, and the Grampian Highlands to the east.

3.2 An assessment of the geology and the hydrogeological features of the area was

conducted with reference to maps produced by the British Geological Survey [2,3,4] .. These maps identified the extent of superficial deposits in the area, mainly marine gravel shingle, sand and silt, along with glacial till over the more elevated areas. The bedrock geology in this part of the Highlands is the Raddery Sandstone Formation, a pebbly red sandstone of Mid Devonian age (395 – 385 Ma), Figure 2. Around 3km to the south, Nigg Hill is an inlier of much older Neoproterozoic metamorphic Psammite and Pelite bedrock (1000 – 540 Ma), likely exposed due to glaciation. It can be concluded that land along the eastern side of the Tarbat peninsula is Neoproterzoic, overlaid with younger Devonian beds, which in turn have been subject to the effects of glaciation, isostatic depression and subsequent marine inundation.

3.3 The large open straths and firths present throughout this part of the Highlands are a consequence of the extensive glaciation that has occurred in recent times, with major ice sheets developing around 850,000 years ago. The last ice sheet disappeared around 15,000 years ago, and the passage of these ice sheets resulted in the heavily glaciated valleys cut into the underlying bedrock, along with significant (10-100m) post-glacial sedimentary deposits.

3.4 The turbines are to be positioned on an area of hard strata on the Tarbat peninsula, in an area of raised seabed. The depth of topsoil varies across the site with topography and aspect, with the fields between the site and Nigg Bay dominated by large depths of gravel, shingle and silt, with 10m of superficial deposits likely under Fearn aerodrome. As a consequence, it can be expected that the groundworks for the turbine foundations will require excavation to a depth of around 3 to 4 metres, creating a stable platform by backfilling with a layer of stone before the concrete structures can be completed.

5 Orkney Sustainable Energy Document OSE/2871 Geology March 2010 4 Superficial deposits

4.1 Peat is not present at the site proposed for the Fearn turbines, and consequently there is no requirement for assessment of peat slide in this area.

4.2 The main superficial deposits are gravel shingle, sand and silt forming raised marine deposits that stretch from Nigg in the south to Cadboll in the east, figure 2, dated as Devensian and Flandrian, or Holocene Interglacial. These are very young deposits, and represent the sea bed during the last ice age and in the warm period immediately after the ice sheets retreated, between 6,000 and 10,000 years ago. The extent of these raised marine deposits suggests that the Cromarty Firth had outfalls near Cadboll and Loch Eye in this period.

4.3 Isostatic uplift and relative sea level fall over the last 5,000 years raised the land, creating the flat plain extending from the intertidal zone at Nigg to Fearn. A similar raised sea bed and sedimentary deposits occurs on Tain shore of the Tarbat Peninsula.

4.4 The raised sea bed is predicted to have a depth of 10m in the area of the wind energy project, and it should be noted that ground level across the site is between 5 and 8m. It should therefore be considered that this part of the Tarbat peninsula will have been below sea level in recent times. Figure 3 is a schematic of the likely coastline around 1000 years ago, based on the evidence of the cliff-like structure north of Loch Eye, along with the various drainage channels, ditches and streams around the area.

4.5 Note that the name “Tarbat” suggests that boats would have been travelling across this area in recent times. The historic sea-level map, figure 4, also reveals that Hill of Fearn, Knock Dhu and Gallow Hill would have been much more prominent, rising out of marsh or shallow water, and it appears likely that there was a navigable shipping route from the Dornoch Firth to the Cromarty Firth, with perhaps a short stretch of portage at Lower Pitkerrie. Figure 3 also shows the route of the older paths and roads around the area, all of which are at around the 8-10m contour; the straight roads and tracks below this height are all modern.

4.6 Drainage conditions and topography have been considered and construction of the project will not have any impact upon drainage or water levels in the area. Access to the site follows existing tracks, and the hardstanding and foundation base will be constructed using existing gravel and stone already present on site. The depth of superficial deposits is such that the project will not encroach upon the lower bedrock.

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5 Hydrology and Hydrogeological Features

5.1 A soil and hydrological investigation of the turbine site has been completed, with reference to the following resources:

• Soil Survey of Scotland, Sheet 21 1: 50000 Scale Map. • Land Use Capability, Sheet 21 1:50000 Scale Map. • OS 1:25000 Explorer Map number 438; Dornoch and Tain • The Design of Field Drainage Pipe Systems; MAFF Ref. 345. • The Climate of the Agricultural Areas of Scotland; Met. Office. • FEH CD-ROM 1999; CEH Institute of Hydrology, Wallingford. • CIRIA C521; Sustainable urban drainage – design manual for Scotland and Northern Ireland • CIRIA C697; The SUDS Manual 5.2 There are no natural rivers, streams or water courses in this area, with a series of man- made drainage channels allowing water to flow south-west towards Nigg Bay. The highest land is to the east of the site, and it should be noted that the drainage system has ensured that Fearn Aerodrome remains dry, Figure 4. Although a largely flat area, the sea at Nigg Bay is around 5m below the ground level at Fearn.

5.3 Loch Eye is 3.5km to the north of the site, and is the shallow remnants of a larger and deeper loch. The outfall from Loch Eye flows around Hill of Fearn, and then west of Fearn Aerodrome to reach the sea at Nigg Bay; most of the drainage channels in the area are routed to this water course, known locally as The Canal.

5.4 The nearest annual rainfall measurement station is at the Alness Gauging Station, 20km south west of Fearn. The landscape and topography differs, nevertheless the average

annual rainfall over the last thirty years has been 1373mm [5] . Rainfall levels in the area are thus moderate for the Highlands, largely due to the rainshadow effect of the large mountainous areas to the south and west.

5.5 There are no significant hydrological features to consider, with the site constructed to ensure that flooding does not occur; there is a network of field drains throughout the area, Figure 5. There will be no requirement to cross water courses, with good access of the public road to the north of the site. The power cable to the local substation next to the A9 will have to cross the canal between Clay of Allen and Balblair, with this work the responsibility of Scottish and Southern Energy.

5.6 It is recommended that care should be taken to avoid pollution in the local drainage system, and it is suggested that SEPA’s Pollution Prevention Guidelines PPG1, PPG5,

PPG6, PPG8 and PPG21 [6] should be adopted by the project. 7 Orkney Sustainable Energy Document OSE/2871 Geology March 2010 6 Ice and Snow Effects

6.1 The Fearn area has a moderate average rainfall of around 1300mm per annum, and consequently snow volumes are low due to rainshadow effects.

6.2 The climate around this part of the Highlands is essentially mild throughout the year, due to marine influences. Heavy snow fall is rare, and on average, the number of days with snow falling is typically around 10 per winter; the winter of 2009/2010 was exceptionally unusual.

6.3 A European study has been completed into the likelihood of icing conditions occurring, and the areas most likely to have blade icing include Germany, Austria, Switzerland,

France and the Spanish border region [7]. The Wind Energy Production in Cold Climates Study (WECO) describes Scotland as a whole as having occasional to light icing conditions, and it is predicted that the Fearn turbines will not be subject to icing effects, as it is unlikely that the relevant ice and snow conditions will occur.

6.4 When considering the possibility of ice throw from a turbine, the same WECO project has the following statement:

“Ice throw is an essential problem when the site of the wind energy power plant is planned to be close to public roads, housing, power lines etc. According to the data and models developed and verified within the project it can be recommended for sites with high probability of icing to keep a distance between the turbines and nearest objects of about (hub height + diameter), or it can be recommended to stop the turbine automatically during the icing period and wind coming from unfavourable directions, if the public safety might be affected by ice throw.”

6.5 The Fearn turbines have a low probability of icing, and in any event the turbine site is well away from housing, public roads and powerlines; the turbines are a minimum of 1km from any neighbouring properties. Consequently ice throw is not predicted to be a significant issue for the Fearn Wind Energy Project.

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7 Hydrological management and pollution prevention

7.1 The construction of wind turbine foundations involves pouring fresh concrete. The nearest watercourses are the drainage ditches on the western side of the aerodrome, and to reduce the risk of pollution run-off it is recommended that all concrete should be brought onto site as a dry mix to minimise the risk of spills. Cleaning of shutters and the washing of equipment should only be done away from the site

7.2 The construction of the turbine foundations will be achieved by excavating down to a depth of around 3 to 4 meters, then backfilling with stone to provide a stable platform 2m below ground level; to mitigate any surface run-off problems this work should only be constructed in dry conditions, with the layer of stone immediately placed on the exposed sub-strata as the construction progresses, with crushed rock aggregate sub- bottoming placed on top of the as-dug rock. Any displaced soil will be relocated into depressions and other areas in the fields around the site.

7.3 Construction should follow the general SUDS guidelines published by SEPA [8] , with a porous construction and a free-draining sub layer.

7.4 To minimise risk of pollution from oils and fuels during project construction, all work should be to COSHH regulations and any machinery, equipment or construction material should be located on areas of hardstanding away from water courses. Any waste should be transported away from the work area and disposed of using standard waste handling procedures.

7.5 Fuel or oil pollution has a drastic affect on water quality should it enter any water courses, and accordingly refuelling activities for construction vehicles and equipment should be restricted to bunded and contained areas of hard standing at fuel storage areas. Good site management should be established:

• Fuel storage should be in double-skinned tanks • No-refuelling should take place within 100m of a watercourse • Equipment should be regularly inspected for leaks and spillages • The site compound should have a full set of absorbent pad spill kits • Any static plant at the substation compound should be bunded • Self-contained portaloos and washing facilities should only be located at hardstanding areas.

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References and bibliography

1 SNH Publications, Scottish Natural Heritage: Inner Moray Firth Landscape Character Assessment.

2 British Geological Survey. Geological Survey One-Inch Survey Map

3 British Geological Survey. Soil Survey of Scotland, 1: 50000 Map No. 21

4 British Geological Survey. Land Capability for Agriculture, Map No. 21

5 SEPA: Rainfall levels and Hydrological Summary for Alness: http://www.nerc-wallingford.ac.uk/ih/nrfa/station_summaries/004/003.html

6 SEPA pollution prevention guidelines: http://www.sepa.org.uk/guidance/ppg/

7 Finnish Metrological Institute. Wind Energy Production in Cold Climates. http://www.fmi.fi/research_meteorology/meteorology_9.html#5

8 Jefferies C. (2004) SUDS in Scotland – The Monitoring Programme , Urban Water Technology Centre, University of Abertay: http://sudsnet.abertay.ac.uk/SNIFFERReport0251.htm

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Figures

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Figure 1: Site Overview

Reproduced from Ordnance Survey Data, Crown Copyright Reserved. License No. 0100031673

Substation

Proposed Cable Route

Switchgear building

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Figure 2: Bedrock geology and superficial deposits

Reproduced with the permission of the British Geological Survey ©NERC. All rights Reserved

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Figure 3: Historic sea levels

Reproduced from Ordnance Survey Data, Crown Copyright Reserved. License No. 0100031673

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Figure 4: Main Hydrological Features

Reproduced from Ordnance Survey Data, Crown Copyright Reserved. License No. 0100031673

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Figure 5: Drainage Ditches

Reproduced from Ordnance Survey Data, Crown Copyright Reserved. License No. 0100031673

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