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

Abstract

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 m3/s (drainage area 322.2 km2), 1042 m3/s (515.4 km2), 1262 m3/s (568.1 km2) and 1484 m3/s (599.6 km2) on the main stem of the Findhorn, with 451 m3/s (171.9 km2) 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 £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 relief. The reconstruction of the 1829 ‘Muckle Spate’ has a significance far beyond its immediate setting in terms of hydrology (confirming the shape of the envelope curve for Britain's most extreme floods), geomorphology (reporting significant and long‐lasting imprints on the riverscape, and confirming the primacy of water‐based erosion early in the nineteenth century) and societal impact (contrasting individual bearing of loss mitigated by charitable relief with the present‐day reliance on flood protection largely provided by the state). The reconstruction also demonstrates the value of reliabl...

High-magnitude flooding across Britain since AD 1750

“…Throughout Lauder's account he frequently comments on human modification of the landscape, partly attributing the severity of the 1829 flood to agricultural improvement and drainage undertaken within the catchment in the decades of the late eighteenth and early nineteenth centuries. Within the instrumental period, the flood of 1970 is the largest, estimated at 2402 m 3 s −1 , but subsequently reduced to 1113 m 3 s −1 following considerable reanalysis, with the 1829 flood estimated to be between 1500 and 1800 m 3 s −1 (McEwen and Werritty, 2007). The present river channel consists of a number of bedrock sections, particularly within the upper catchment, with alluvial highly mobile sections within the lower catchment susceptible to lateral avulsion, though McEwen and Werritty (2007) note limited migration in most channel sections since the present channel was excavated during the 1829 flood.…”

“…Within the instrumental period, the flood of 1970 is the largest, estimated at 2402 m 3 s −1 , but subsequently reduced to 1113 m 3 s −1 following considerable reanalysis, with the 1829 flood estimated to be between 1500 and 1800 m 3 s −1 (McEwen and Werritty, 2007). The present river channel consists of a number of bedrock sections, particularly within the upper catchment, with alluvial highly mobile sections within the lower catchment susceptible to lateral avulsion, though McEwen and Werritty (2007) note limited migration in most channel sections since the present channel was excavated during the 1829 flood. There are no severe flood events recorded on the Findhorn between the flood of 1829 and the start of the instrumental series in the 1950s, from which reliable estimates can be derived; however, it is notable that several floods are described in the period between 1914 and 1924, though accurate estimates of their discharge are not achievable from the available records.…”

Quantitative historical hydrology in Europe

“…7). In the case of the River Findhorn in UK, the official gauged discharge for the 1970 flood was initially 60 % higher than the reconstructed peak flow for the "Muckle spate" flood of 1829, although later the 1970 peak flow was recalculated below the 1829 flood (McEwen and Werritty, 2007).…”

Groundwater, flooding and superficial deposits in the Findhorn catchment

“…The Forres area in NE Scotland was subjected to one of the most catastrophic floods in UK history when the River Findhorn flooded in 1829 (McEwen and Werritty, 2007). Since that time, the floodplain has been built on as the town of Forres has expanded.…”