Allt Bheadhair, a tributary of the Nethy
 
Upper peat developed on bedded organic sands that may have accumulated in a small pond. The underlying coarse gravel may have been deposited by an ancient flood of this stream. It rests at the base of the section on an older peat with tree stumps and roots. No investigation has been made of this site but the sequence may all belong to the last few thousand years of the Holocene.

River Spey at Kingussie

 

 

 

 

 

 

Detailed reconstruction of the 1829 Findhorn flood

Detailed account of the 1829 flood around Nethy Bridge

Planning for future floods in Moray

 

Floods

Definition: a discharge in excess of the capacity of the stream channel, when water spreads across the floodplain

Major changes in river systems occur in response to extreme precipitation events and the consequent floods. In the Cairngorms and surrounding area, three meteorological causes of flooding may be recognised:

  • Slow-moving depression systems and associated relief rainfall
  • Heavy snowfall followed by rapidly rising temperatures, snow melt and further rain
  • Intense summer convectional storms

The scale of the flood hazard in and around the Cairngorms can be judged in relation to historic floods. The 1828 floods of Moray were probably the most extreme experienced anywhere in the British Isles over the last few centuries. More localised events such as those in 1956 (Baird and Lewis, 1957) and the 1978 flood on the Allt Mhor took out bridges and caused widespread damage. The potential of water levels in the Spey, in particular, to rise spectacularly is probably not appreciated widely enough but it was brought home to me in the 1980s by the old farmer at Dalfaber. This farm is now lost to the development of the timeshare at Aviemore,. The farmer showed me where the water level had reached in a flood he remembered on his back door step!

Allt Mhor flood of August 1978

This relatively recent flood on the Allt Mhor, draining the Cairngorm ski slopes, demonstrates the significant flood hazard represented by mountain streams (McEwen and Werritty, 1988).

The flood on the 4th August was triggered by an intense summer thunderstorm in which 33.5 mm of rainfall fell in 1 hour, equivalent to around 5% of the average annual rainfall of Edinburgh.

The high discharge caused severe erosion of gravel bluffs overlooking the river at the below the Sugar Bowl and mobilised boulders over 0.5 m in diameter. The road bridge was swept away and fragments of tarmac can still be found in the gravel bars below the present bridge.

Moray Floods of August 1829

The extensive floods of August 1829 represent without doubt the most severe floods in Scotland over the last 200 years. All the rivers in the Grampians, from the Nairn to the South Esk at Montrose rose to exceptional levels in response to a severe frontal storm.

The discharges were enormous and can be judged from line drawings after the event.  The Findhorn at Randolph's Leap reached 1450 cumecs, the Spey at Boat o'Brig 1665 cumecs and the Dee at Cairnton 1900 cumecs. Each discharge may represent the level of flood expected only once every 500-1000 yr on average. The peak discharge of 2400 cumecs on the lower Findhorn in 1970 (after 150 mm of rainfall over the lower Findhorn and 100 mm over lower Spey) suggests however a shorter return period (Green, 1971). The classic account of the Moray floods remains gripping reading (Lauder, 1830).