Avalanche protection

Avalanche protection at Fljótsdalur

Fljótsdalur - Iceland

  • Fljotdalur

Verkís services was appraisal study and technical avalanche design, geotechnical design, tender documents and consultation during construction.

 Sizes: 13,5m high and 60m long
 Project time:  2005 - 2007

Project overview:
The substation for the Kárahnjúkar hydropower plant is located at the foot of mountain Teigsbjarg in southern Fljótsdalur. The mountain reaches up to 500m a.s.l.  Snow accumulation in the mountainside is only moderate during normal winters. However, north-westerly winds can cause large amounts of snow to drift from the mountain plateau and accumulate in a small bowl between two cliff belts in the hillside and form cornices in the upper cliff belt.

People will not be based permanently in the switchgear building. The design of the defence measures is therefore based on fulfilling requirements for operational safety of the power lines. To meet the requirements, the defences are designed to prevent an avalanche with a 10.000 year return period from damaging the building. 

A triangularly shaped dam, here referred to as a splitter, was designed to split avalanches heading towards the building and deflect them to either side of the building. The splitter is positioned close to the switchgear house and reaches as high up into the hillside as possible to minimize the deflecting angle of the dams and thus the height of the structure. All three sides of the splitter are steep or almost vertical due to the lack of space above the house.

The technical avalanche design is based on shock dynamics in high speed dense granular flows, such as snow avalanches. The method lead to the design of a lower deflecting dam than previous design methods would have suggested. Shock dynamics now form the basis of new European design guidelines for avalanche defence dams (EUR 23.339).

The splitter is 60m long and 9m high closest to the slope. Its height increases to 13,5m above the ground on a 15m long stretch. The steep sides of the splitter are constructed with a reinforced earth system using 40.000 m³ of material from the tunnels in Teigsbjarg as backfill. The dam sits on a 3m thick, packed earth fill. Trenches were shaped at both sides of the splitter to direct water away from the foot of the dam and drains the area.