'The Muckle Spate of 1829': the physical and societal impact of a catastrophic flood on the River Findhorn, Scottish Highlands

On 3 August 1829, north-east Scotland recorded one of the most severe catastrophic floods in modern UK history. Sir Thomas Dick Lauder's An account of the great floods of August 1829 in the province of Moray and adjoining districts (1830) provides a detailed eyewitness account that can be used to reconstruct the flood. This paper reconstructs the hydrometeorology of the flood, assesses its geomorphological and societal impacts and provides a context for assessing present-day flood risk management. The flood was generated by a slow-moving depression in the Moray Firth, which produced an unstable northerly airflow over the NE Grampian Mountains and a minimum 24 hour rainfall of 95 mm. The River Findhorn, one of the most severely affected drainage basins, was subject to detailed analysis by Lauder, including the reporting of numerous flood levels on bridges and within bedrock gorges. Reconstruction of flood flows at five of these sites using Manning's equation and moving successively downstream yields peak flows of$711 m^3/s$(drainage area$322.2 km^2$),$1042 m^3/s$($515.4 km^2$),$1262 m^3/s$($568.1 km^2$) and$1484 m^3/s$($599.6 km^2$) on the main stem of the Findhorn, with$451 m^3/s$($171.9 km^2$) on a major tributary. Each peak flow based on a Manning's n of 0.04-0.08 represents the optimal value within limits which vary between -25% to +33% and all lie just within the upper boundary when plotted in relation to the envelope curve for catastrophic floods within the UK. Lauder also provides a detailed account of the geomorphic impacts of the flood in the Findhorn valley. Bedrock reaches and 'mixed' alluvial/bedrock-controlled reaches proved to be robust and registered minimal change, but alluvial reaches reported widespread bank erosion and slope failures with extensive sheets of sand and gravel deposited downstream on valuable agricultural land. Meander cut-offs occurred and many new channels were excavated, especially in the coastal lowlands where the present-day channel broadly follows that excavated in 1829, attesting to the longevity of the flood's impacts. The immediate societal impact included eight fatalities, destitution for at least 289 families, large-scale destruction of roads and bridges, losses for estate owners approaching [POUND SIGN 2.83 million] (2005 prices) and a major shock to a relatively prosperous rural economy. Human response and mitigation took the form of fatalistic acceptance, bearing the loss and dependence on local charitable reli