With work finally underway by Highways England to fix the flood damaged A591, the geo-engineer who shot to fame after featuring in Cumbria County Council’s film of the survey work done by Capita on the road spoke at our AGM on 10 Feb.
Dr Simon Ferley, Principle Geo-engineer, gave a fascinating and at times mind-boggling introduction to the often unpredictable behaviour of soil on slopes. We were introduced to the various factors that give soil strength – such as cohesion (the ‘stickum’ between particles) and friction, - and the threats to soil cohesion which can lead to landslides of the kind we experienced in December.
It was a practical, hands on demo too – with dry, damp and wet soil samples for attendees to poke and a neat demonstration of the effect water has on the weight of rocks with the help of a bucket, some string, scales and a brick. When waterflow doubles in speed, it can move treble the size of boulders. Which is why the unprecedented intensity of rainfall and velocity of run off in December moved the previously unmoveable.
Water velocity can be slowed by ensuring channels under bridges are kept clear of debris to avoid the funnelling effect of blockages and the realignment of streams and rivers to re-introduce meanders can also help ‘slow the flow’. The design of domestic and business developments should be considered as rainwater runoff that discharges directly into streams can exacerbate water velocity.
Dr Ferley highlighted also that the erosion of footpaths can contribute to landslips. Plant roots keep the soil from sliding off the mountain so good vegetation cover, particularly on our thin upland soils, is vital. Our business fundraisers for Fix the Fells may like to know that they are helping soil stability with their efforts as well as ensuring good access provision to the hills for visitors.
Finally, as we wait impatiently for the A591 to be restored by the end of May, Dr Ferley issued a stark warning. That even prior to Storm Desmond there were known ‘slope instabilities’ alongside roads in the area. These potential landslips are subject to ongoing monitoring but any action would necessitate controlled road closures which are often unpopular with residents and tourism businesses alike. Dr Ferley urged that prevention is far easier than dealing with the aftermath of landslips like those affecting the A591.
Dr Ferley was speaking in a personal capacity. We are grateful that he so generously gave us his time and grateful also to the Low Wood Bay Hotel for providing us with a venue, beverages and cakes.