OSE3506 Chapter 4

Ore Farm Wind Energy Project Geology, Superficial Deposits and Hydrology Orkney Sustainable Energy Ltd 6 North End Road Stromness Orkney KW16 3AG 01856 850054 [email protected] www.orkneywind.co.uk Orkney Sustainable Energy Ore Farm Wind Energy Project Report OSE/3506 Chapter 4 Orkney Sustainable Energy Document OSE/3506 Chapter 4 March 2011 Report OSE/3506 Chapter 4 March 2011 Client: Orkney Wind Farms Ltd Haybrake Farm Lyness Assessment: Richard Gauld BSc(Hons) IEng MInstMC Dip.GeoSci 1 Summary 1.1 A small wind farm is proposed for a coastal pasture part of a farm at Lyness in Hoy. The project will consist of two medium sized wind turbines, an upgraded access track and a switchgear building, all to be owned by Orkney Wind Farms Ltd, a local development company. 1.2 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, along with consideration of possible ice and snow effects. 1.3 The site and route of the access track have been surveyed 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, two days were spent on walkover surveys, identifying any surface water features, including drains and burns. 1.4 The turbine site appears geologically stable, with the turbines located on fault-free Lower Eday sandstone, and there are no water crossings or other hydrological impacts to consider. 2 Orkney Sustainable Energy Document OSE/3506 Chapter 4 March 2011 2 Landscape and Geomorphology 2.1 The proposed location for the development is the largely flat pasture to the west of Ore Farm at Lyness on Hoy, 18m above sea level. On one side the site is on the margin of arable grazing land, where the land has been cultivated and improved from moorland over many years, and on the eastern margin are the remains of the World War 2 base. The turbine positions follow a linear pattern, running due north-south. The access to the site would follow the existing track to the Hoy Community wind turbine, with only short stretches of new track required. 2.2 Project analysis has considered the Orkney Landscape Character Assessment, and the wind turbines and switchgear building are positioned at the edge of Inclined Coastal Pasture [1] . Ore Farm has a range of mainly small fields, clearly visible when viewed from the east. It should be noted that the western edge of Ore Farm marks the boundary between the managed farmland and the moorland hills that cover most of the island; the project has been located to be distant from any environmentally protected areas. 2.3 The geomorphology of the site is to a large degree controlled by the underlying geology, with the resultant landscape draped over the base geology and eroded through time. In the current period the landscape has been dominated by glaciation, which has moulded the underlying geology with superficial deposits of boulder clay, with peat deposits draped over the moorland hills [2] . The landscape has seen post-glacial erosion over the past 10,000 to 15,000 years, and periods of climate change have altered the area; the poorer quality superficial deposits across the more elevated parts of the island are relatively recent, suggesting that much of this area has seen drier and warmer periods. 2.4 Anthropic influences in recent years have altered the landscape. This part of Hoy was the centre of a large naval base during World War 2, with many remains still present; there are extensive derelict concrete foundations over much of the farm. The fields are rough grazing, and are not particularly productive, although drainage and land management techniques have created the group of fields being used by the development. There are also various access tracks running between the fields, reducing the need for any additional infrastructure. 3 Orkney Sustainable Energy Document OSE/3506 Chapter 4 March 2011 3 General Geology 3.1 An assessment of the geology and the hydrogeological features of the area was conducted with reference to maps produced by the British Geological Survey, and with reference to the resources provided on the Orkney geology web site; http://www.landforms.eu/orkney/ . These assessments confirmed that this area is mainly underlain by Devonian Old Red Sandstone sedimentary rock. 3.2 Hoy is typical of Orkney, and is dominated by the Devonian Sandstone; Orkney is a raised part of Lake Orcadie, a former lake basin dating from around 380 million years ago, that has resulted from sediment laid down on the lake bed. These sediment rocks rest on much older basement granites and gneisses, which are exposed at Yesnaby and Stromness to the west of Mainland Orkney. 3.3 The basement rocks are a mixture of granite, gneiss and schists, which formed part of the Caledonian mountain chain 400 million years ago. These rocks originally enclosed Lake Orcades which became the focus of erosion and the deposition over time; this sediment formed Old Red Sandstone, which now largely obscures the basement rock complex. 3.4 Tectonic activity caused the sediments to become folded and faulted, creating a range of hills, which was then subjected to erosion and submergence; Hoy and South Walls consist of gently sloping Devonian rocks, known locally as Upper Stromness flagstone and Eday and Hoy Sandstone, Figures 1 and 2. Note that the Hoy and Eday Sandstones were laid down in dry desert conditions, whereas Stromness flagstone was a marine deposit and has a more laminate structure. The turbines are all sited on Lower Eday sandstone. 3.5 The rounded landforms present throughout Orkney are a result of the extensive glaciation that has occurred, with major ice sheets developing around 850,000 years ago. The last ice sheet disappeared around 15,000 years ago, leaving exposed striations in the more mountains parts of north Hoy. The passage of these ice sheets also resulted in the extraction of sea bed sediment, producing the layer of till and boulder clay that covers much of the southern parts of the island. 4 Orkney Sustainable Energy Document OSE/3506 Chapter 4 March 2011 3.6 Note that the Orkney Landscape Character Assessment distinguishes between Hoy and Eday Sandstone, however recent studies show that the two rocks are contemporaneous, with Hoy bedrock most likely to be upper Eday Devonian sandstone. Figure 1 also shows the location of the major faults across this part of Orkney; the Ore Farm project avoids all known faults. Devonian igneous rocks are not common in Orkney, however lava flows can be observed at the base of the Kame of Hoy at the northern edge of the island, volcanic ash deposits are prominent in the cliffs at the west end of Rackwick beach, and volcanic vents and pipes can be seen at the Round Hill in Hoy, and at Melsetter, to the south of the turbine site. Figure 1 – Bedrock Geology (SNH LCA) Lower Eday sandstone Upper Stromness flagstone Peat deposits Alluvial deposits Till Figure 2 – Solid geology and superficial deposits (BGS) 5 Orkney Sustainable Energy Document OSE/3506 Chapter 4 March 2011 4 Hydrology and Hydrogeological Features 4.1 Annual rainfall in Orkney has been measured to be 1030mm at Kirkwall, averaged over the last thirty years [5] . There is variation across Orkney, with Hoy seeing higher levels that the east, however rainfall is relatively low, largely due to the rainshadow effect of the mainland Scotland hills to the west and south. 4.2 Sedimentary sandstone is a good aquifer when fractured, however the flat land around the turbine site has resulted in water flowing quite slowly on the surface of the land, evident by the poorer quality moorland and peat deposits to the west and north of the turbine site. 4.3 There are no significant hydrological features in the area, and there are no water crossings to consider. The field boundary to the west of the site has a drain which feeds into Ore Burn, to the north of the site, ultimately draining into Scapa Flow on the eastern side of this part of Hoy, Figure 3. Peat Deposits Ore Burn Flow direction Hardstanding for on-site storage and fuel handling Field drain Field drain Burn Figure 3 – Hydrological features 6 Orkney Sustainable Energy Document OSE/3506 Chapter 4 March 2011 5 Superficial deposits 5.1 The solid geology of Orkney was modified by glacial action during the ice ages, the last of which reached its maximum extent 18,000 years ago. The main effects of ice movement in this area were generally to smooth out the topography and to deposit glacial till boulder clay; peat deposits have subsequently become established over the hills to the west. 5.2 The till deposits have resulted in moderate quality rough grazing land, particularly over the Middle Eday bedrock. Where the soil is located to the west of the turbine fields, and where drainage has been poor, the superficial deposits have become peaty, resulting in the moorland evident over much of Hoy. Figure 2 shows that the whole area has been draped by a smooth layer of till and boulder clay topsoil, with peat over the western hills. 5.3 The turbines are to be located in an area of improved agricultural topsoil on boulder clay and sedimentary sandstone. The soil type on the site is defined by the Soil Survey of Scotland as a poorly drained gley, derived from Stromness and Eday sandstone [3] .

Load more