Scottish debris flow events of August 2004

In August 2004 Scotland experienced rainfall substantially in excess of the norm. Some areas of Scotland received more than 300% of the 30-year average August rainfall, while in the Perth & Kinross area figures of the order of between 250% and 300% were typical. Although the percentage rainfall during August reduced to the west, parts of Stirling and Argyll & Bute still received between 200% and 250% of the monthly average (Source: http://www.metoffice.com/climate/uk/2004/august/maps.html). The 30-year average rainfall for August in Scotland varies between 67 mm on the east coast and 150 mm in the west of Scotland (Anon 1989). The rainfall was both intense and long lasting and a large number of landslides, in the form of debris flows, were experienced in the hills of Scotland. A small number of these intersected the trunk or strategic, road network, notably the A83 between Glen Kinglas and to the north of Cairndow (9 August), the A9 to the north of Dunkeld (11 August), and the A85 at Glen Ogle (18 August). These locations are illustrated in Figure 1. Fig. 1 Map showing the trunk and motorway network in Scotland (© Crown Copyright). The locations of the three main debris flow event areas in Scotland in August 2004 are also shown. While there were no major injuries to those affected, 57 people had to be airlifted to safety when they became trapped between the two main debris flows at Glen Ogle. However, the real impacts of the events were economic and social, in particular the severance of access to and from relatively remote communities. The A85, carrying up to 5600 vehicles per day (all vehicles two-way, 24 hour AADT – Annual Average Daily Traffic), was closed for four days. The A83, which carries around 5000 vehicles per day, was closed for slightly over a day …