Lochs Bi and Druidibeag (Potentially Vulnerable Area 02/07)

Local Plan District Local Authority Main Catchment 02 Outer Comhairle nan Eilean Siar Coastal

Background

This Potentially Vulnerable Area (PVA) The main road (A865) passes through covers the northern and north-western the western side of the PVA. Most of the parts of South Uist from Tobha Mor on the properties are located to the west of the west coast to Loch Eynort on the east. It road. covers an area of 130km² containing numerous lochs in the north and west of The total Annual Average Damages the PVA including Loch Bi and Loch (AAD) for all sources of flooding are Druidibeag (Figure 1). The west coast is £144,000. The majority of these AAD dominated by machair. are from coastal flooding (77%), with river and surface water flooding both contributing a smaller proportion of the overall damages (see Figure 2).

Figure 2: Annual Average Damages by Figure 1: Lochs Bi and Druidibeag Flood Source Potentially Vulnerable Area

This area was designated as a PVA due to flood risk to roads, cultural heritage sites and the Loch Druidibeag National Nature Reserve based on information available at the time of the National Flood Risk Assessment in 2009. The PVA was extended to include areas to the north around Iochdar as a result of consultation with the local authority. Designation as a PVA means that further investigation of that flood risk was required. This has been carried out based on the flood hazard and risk maps published by SEPA in January 2014 together with input from the Local Plan District Partnership.

Summary of Impacts from all sources of flooding

The majority of the Annual Average Damages are a result of flooding to residential properties with some damages to agricultural land and transport links also contributing to the overall total. The majority of residential properties are at risk from coastal flooding. The number at risk of coastal flooding increases significantly for the more extreme events such as at the villages of Clachan and Kilaulay, which are located in low lying areas. The few non-residential properties at risk of flooding are at risk from surface water flooding.

There are several cultural heritage sites at risk of flooding including Caisteal Bheagram, the Castle at Drumsdale. The majority of the sites are designated as Scheduled Ancient Monuments and are prehistoric domestic and defensive sites. Cultural heritage sites do not contribute to the AAD total as it is difficult to quantify a monetary value for them.

Areas of environmentally designated sites are at risk of flooding. The sites include Howmore Estuary, Lochs Roag and Fada Site of Special Scientific Interest (SSSI), Loch Druidibeg SSSI, South Uist Machair Special Area of Conservation (SAC), South Uist Machair and Lochs Special Protection Area (SPA).

Table 1 presents a summary of the receptors at risk from all sources of flooding in the different return periods (different probabilities of flooding in any one year). The contribution from the different receptors to the overall damages (by return period) is shown in Figure 3.

Figure 4 shows the location of receptors that are at medium to high risk of flooding from all sources in the PVA.

Table 1: Summary of Flood Risk from all sources High Risk Medium Risk Low Risk

1 in 10 year 1 in 200 year 1 in 1000 year Number of Residential 21 31 36 Properties at risk (out of 251) Number of Non-residential 4 4 5 Properties at risk (out of 89) Number of People at risk 46 68 79 Community Facilities at risk 0 0 0 Utilities at risk 0 0 0 Transport Links at risk Roads (66 locations) Roads (77 locations) Roads (79 locations) Designated Areas (km 2) at 53 km 2 63 km 2 63 km 2 risk Number of Cultural heritage 7 12 12 sites at risk Agricultural land at risk (km2) 7 km 2 9 km 2 9 km 2

Figure 3: Damages by receptor and return period for flood risk from all sources Figure 4: Location of receptors at medium to high risk of flooding from all sources in the Lochs Bi and Druidibeag PVA

Summary of existing local actions to manage risk

All of the structural measures to manage existing flood risk are located along the west coast of the PVA. There is a rock revetment around the coast at Baile Gharbhaidh, rock and netting at the Ministry of Defence range at Ardivachar, and hard defences at Iochdar and the causeway linking South Uist to Benbecula.

A flood alleviation scheme at the Clachan in Iochdar was implemented after the January 2005 storm consisting of road level raising and rock revetment coastal protection. Gualan Island situated to the west of the South Ford acts as a barrier island providing protection to the inner coastline from Atlantic storm waves but was breached during the January 2005 storm and remains in a severely eroded state.

Loch Bi to the north of the PVA is an extensive freshwater/brackish water body which drains mainly to the sea on the east of the island to Loch Sgioport and also to the north at Clachan. Sea water is excluded from Loch Bi by floodgates but these are currently in a state of disrepair.

Freshwater lochs located in the south of the PVA are interconnected by a system of drainage ditches and they drain to the sea through a drainage canal (the Leacach How) and the Howmore River.

Comhairle nan Eilean Siar takes flood risk into consideration as part of decisions related to land use planning, as outlined in Scottish Planning Policy. This includes ensuring that new developments are not permitted in areas at risk of flooding and that all new developments do not increase flood risk elsewhere.

Floodline, SEPA’s flood warning service, provides flood alerts for the .

Summary of Objectives to manage risk in PVA

Local Plan District

Initial Objective Indicator

Avoid an increasing the number of residential and From an estimate of 224 non-residential properties at risk from all sources of residential properties flooding. From an estimate of 152 non- residential properties

Lochs Bi and Druidibeag (PVA 02/07)

Initial Objective Indicator

Reduce number of people at risk from coastal From an estimate of 53 flooding people

Initial Objective Indicator Reduce disruption to transport at high risk from 33 road locations at high risk coastal and river flooding

Initial objectives for cultural heritage and environmental designated sites may be added when information is available from the relevant body at the end of the objectives sections.

Summary of Measures to achieve Objectives

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