SECTION 3: MAIN CATCHMENTS, COASTAL AREAS & SURFACE WATER MANAGEMENT WITHIN OUTER HEBRIDES LOCAL PLAN DISTRICT CHAPTER 4.4: COASTAL FLOODING Benbecula, South Uist & Barra Coastal Area Local Plan D istrict Local Authorit y Outer Hebrides - 02 Comhairle nan Eilean Siar The Benbecula, South Uist & Barra Coastal Area (Figure 1) has a coastline with an approximate length of 830km. It comprises the southern portion of the Outer Hebrides Local Plan District (LPD) and includes the islands of Benbecula, South Uist, and Barra. This coastal area contains three of the eight Potentially Vulnerable Areas (PVAs) in the Outer Hebrides including those which have the greatest flood risk. The three PVAs are: Benbecula (02/06); Lochs Bi and Druidibeag (02/07); and, Bornish to Boisdale (02/08). The east coast is typically embayed with many inlets, and sea lochs. By contrast, on the west coast, machair grasslands often flanked with sand dunes are the predominant land form extending up to 2 kilometres inland from the foreshore. Many of the settlements are located close to the coastline while others are situated at the landward limit of the machair where it joins with inland land forms such as glacial deposits, rock or peat. 02 South Uist, Benbecula and Barra coastal Page 1 of 12 area Version 1.0 Figure 1: Benbecula, South Uist and Barra Coastal area 02 South Uist, Benbecula and Barra coastal Page 2 of 12 area Version 1.0 4.4.1 Coastal Flooding Impacts Main urban centres and infrastructure at risk There are between 101 and 250 residential properties and between 11 and 50 non- residential properties at medium to high risk of coastal flooding. Approximately 95% of properties at risk in the medium to high risk event are located within the three PVAs. Figure 2 shows the locations of the residential property at risk of coastal flooding. The location with the largest number of residential properties at medium to high risk of coastal flooding and with the highest level of AAD is Balivanich, Table 1. There is also coastal flood risk in the Dalabrog and Iochdar areas on South Uist and Gramasdail, Creagorry and Lionacleit on Benbecula. Table 1 – Main areas at risk of coastal flooding No of residential properties at Annual Average Damages Locations flood risk (at the 1 in 200 year flood event) Balivanich 50 to 100 £392000 There are approximately 150 road segments at risk of coastal flooding in the medium to high risk event. The main routes affected include the A865, B891, and B892. History of Flooding In January 2005 a severe storm hit the west coast of Scotland including the Outer Hebrides. During the storm five people from the same family died when their cars were swept from a coastal road in Iochdar, South Uist as they were trying to escape from flood waters. Widespread flooding occurred in many locations, particularly on the west coast, with roads, agricultural land, houses and other buildings being inundated with sea water. Although there are no other officially recorded flood events in this coastal area coastal flooding has occurred on numerous occasions when storm surge and high tides coincide. Economic activity The annual average damages (AAD) from coastal flooding in the Benbecula, South Uist and Barra coastal area are estimated to be approximately £577,000. This accounts for 41% of the total damages for the LPD from all flood sources. These AADs are made up from a variety of damage categories including residential property, non-residential property, agriculture, roads, damage to vehicles, and emergency service costs. For the Benbecula, South Uist and Barra Coastal Area the vast majority of the damages (65%) are to residential properties. The locations where economic damages are likely to occur due to coastal flooding are shown in Figure 3. This includes damages around the majority of the coastline as a consequence of flooding of approximately 20km 2 of agricultural land at medium to high risk of coastal flooding. The areas that have the highest damage densities are around Balivanich on Benbecula and Kilpheder on South Uist. 02 South Uist, Benbecula and Barra coastal Page 3 of 12 area Version 1.0 Areas of Environmental and Cultural Importance at risk of flooding The Western Isles has hundreds of archaeological sites situated along the coast and the low lying areas beyond. Many of these are in a relatively good condition with minimal disturbance. The main threat to these sites is coastal erosion. In relation to the many cultural heritage sites at risk of coastal erosion, assessment surveys and excavations such as those run by the SCAPE Trust (Scottish Coastal Archaeology and the Problem of Erosion), and information recorded by other agencies have helped to highlight this issue. There are 16 cultural heritage sites at medium to high risk of coastal flooding in this coastal area. All of these are Scheduled Ancient Monuments and the majority are prehistoric domestic and defensive sites, however there is also a standing stone at Pollachar, and three secular sites including Caisteal Bheagram and the castle at Drimsdale. There is approximately 50km 2 of environmentally designated areas at medium to high risk of coastal flooding. A study conducted shortly after the January 2005 storm has shown that machair habitats are resilient to saline incursion possibly due to the high level of interaction between freshwater/brackish water in the inland machair loch system and the water table (Angus S. & Rennie A.F. 2012). The ability to restore surface water salinity levels through a unified subsoil/surface water table may be an advantage in respect of short duration flooding, but if saline flooding is more persistent, either due to failure of drainage systems or to more frequent marine inundation, this dispersal effect may become a liability as it would result in saline contamination equally of ground and surface water. Management of drainage systems is important for flood water dispersal and for maintaining current levels of salinity in the water table. Adjustments may be required to cope with increased saline inflow caused by rising sea level, but as sea level rises still further it will become more difficult for the drainage system to cope. Ground nesting birds may also be adversely impacted by coastal flooding. 02 South Uist, Benbecula and Barra coastal Page 4 of 12 area Version 1.0 Figure 2: Benbecula, South Uist and Barra coastal area residential properties at risk of coastal flooding 02 South Uist, Benbecula and Barra coastal Page 5 of 12 area Version 1.0 Figure 3: Annual average damages from coastal flooding 02 South Uist, Benbecula and Barra coastal Page 6 of 12 area Version 1.0 4.4.2 Managing Flood Risk along the Coastline Existing flood protection schemes There are numerous coastal defences throughout the Benbecula, South Uist and Barra coastal area, some of which provide flood protection in addition to protection against erosion. Details of the defences present in the three PVAs can be found in the individual PVA reports. Comhairle nan Eilean Siar is the planning authority for the Outer Hebrides and is required by Scottish Planning Policy to consider flood risk issues when determining planning applications. The Comhairle adopts differing approaches for proposals depending on the level of risk and developers may be required to provide a Flood Risk Assessment. The Scottish Environment Protection Agency (SEPA) is Scotland's flood warning authority. It provides flooding updates and advice on being prepared for flooding. SEPA operates a general flood alert scheme for the Outer Hebrides but there are no specific flood warning target areas. The Local Authority Emergency Planning Unit works with SEPA in helping raise awareness of flood risk and the dissemination of warnings to the community. They work with emergency services in response to severe flooding events, in providing shelter in the event of evacuations and with communities and businesses on resilience and recovery. SEPA operates a general coastal flood alert scheme for the Outer Hebrides but there are no specific flood warning target areas identified. Awareness raising campaigns & community flood action groups There are two community flood action groups, the Iochdar Flood Action Group and the Middle District Flood Action Group which were formed in the immediate aftermath of the January 2005 storm. Public meetings and workshops have been held in recent years to discuss flooding and coastal erosion issues particularly in Benbecula and South Uist. These events have been well attended reflecting the importance of coastal issues to the local population and the willingness of local people to be involved in decision-making and implementation of schemes. Organisations that have been involved include the Comhairle; Scottish Natural Heritage; Coast Hebrides, the local coastal partnership ( www.coasthebrides.co.uk ); Stòras Uibhist, the community land owner; the CoastAdapt project (www.coastadapt.org); and Oxfam Scotland who provided community support. Comhairle nan Eilean Siar was lead partner in the CoastAdapt EU project which aimed to safeguard people living in North Atlantic coastal communities and help them adapt to the impacts of climate change. Flood Risk Management Studies There are number of studies into flood and coastal erosion risk for this Local Plan District. The main studies are listed in Table 2. 02 South Uist, Benbecula and Barra coastal Page 7 of 12 area Version 1.0 Table 2. Flood and Coastal Erosion Risk studies relevant to the Benbecula, South Uist and Barra coastal area. Study Title Source Survey of Coastal Erosion in the Western HR Wallingford, 1995 Isles (Management Units 31 to 44) Coastal Zone Assessment Study (for SCAPE, 2005 Archaeological Assets) Report on Condition of Drainage Systems Stòras Uibhist, 2006 in Benbecula and South Uist An Ataireachd Ard: the Uist storm of Angus S.