Neil Macdonald | Sources: Neil Macdonald on Epigraphic Records: A Valuable Resource in Reassessing Flood Risk and Long-term Climate Variability | Environmental History, 12.1

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NEIL MACDONALD ON EPIGRAPHIC RECORDS: A VALUABLE RESOURCE IN REASSESSING FLOOD RISK AND LONG-TERM CLIMATE VARIABILITY

HISTORICAL FLOOD RECORDS are increasingly being recognized as a valuable tool in understanding the long-term frequency and magnitude of extreme events—events that have rarely been recorded using conventional river flow recording approaches (within the UK there are relatively few records in excess of fifty years of length, with only a handful over seventy-five years length).¹

Epigraphic markings—the lines, nicks, or scores indicating the level of previous floods—are one type of historical record. They can be found in many urban centers with major rivers and are normally located on structures near the river that can be easily viewed during flood events. As a result, most records are preserved on bridges (or on their buttresses) and walls (defensive structures). Epigraphic records represent a valuable tool in understanding the nature and frequency of extreme flood events and, on rare occasions, also contain information relating to droughts. Smeaton's Bridge in Perth, Scotland, for instance, contains numerous markings relating to floods, but also information on a low flow on the River Tay from the late nineteenth century (see Figure 1).² These markings provide valuable records of rare events, events often missing from conventional records simply because of their failure to occur in the relatively short period over which scientific river flow information has been collected. The presence of an epigraphic record often can be attributed to an individual's interest or to the presence of a significant event; an event of such an extreme nature that no living individual could recall an event of such magnitude. As a result, the level is marked into a wall or bridge for posterity so that future generations will have some means of recounting the extent of the flood.³ As a result of this initial record, future flood events may be recorded, providing a long contextual chronology of floods, which, over time, produces a valuable record of high magnitude-low frequency events.

Figure 1: Smeaton's Bridge Epigraphic Flood and Drought Markings, Perth, Scotland.

Photo courtesy of the author.

A series of high magnitude floods in Europe in the last decade has led to concerns over the frequency of such flood events in a changing climate. The inclusion of historical records is increasingly being seen as a valuable tool in the reassessment of flood and drought risk. Epigraphic records present a useful contribution to the re-evaluation of flood risk in many sites within Europe, par-ticularly for older cities, such as Perth, Scotland (see Figure 1), Nottingham, Eng-land (see Figure 2), Vallon, France, Cra-cow, Poland, and Eibelstadt, Ger-many, among oth-ers.⁴ Often these sites have a long history of residence, or importance as monastic, trade, or governmental cen-ters. The presence of historical flood records does not necessarily rely upon long residency at a site, so that epigraphic records can contribute to understanding the long-term flood magnitude-frequency relationship on some rivers that have relatively short population residency timescales.

Figure 2: Trent Bridge Epigraphic Flood Markings, Nottingham, England.

Photo courtesy of the author.

Inevitably, as the markings are often located on structures close to the river, they are occasionally removed during or after large floods as a result of structural failure. Therefore, the oldest records may have been removed or damaged before a town's residents identified a bridge design that could stand up to the impact of a flood. The documentary accounts often indicate that several bridges were washed away before a more enduring bridge was built; for instance, the records for the River Tyne indicate that of all the bridges spanning the river in 1771, only the bridge at Corbridge was not lost during a devastating flood.⁵ The presence of informal markings also leads to a loss of data; an example from near York in northern England can be seen in Figure 3. The 1978 flood marking is not easily discernable, particularly in comparison to the two subsequent flood events; it is likely that in twenty more years this mark will be undistinguishable unless inscribed into the wall.

Figure 3: Informal Markings along the River Ouse Near York, England.

Photo courtesy of the author.

The immoveable quality of epigraphic records is significant because archival accounts frequently document an event only many years after its occurrence (and often are authored by an individual who did not witness the flood), inevitably increasing the likelihood of embellishment or inaccuracy.⁶ Epigraphic markings are frequently inscribed during or soon after the flood event, giving them greater credibility.

Epigraphic records have been used principally for flood frequency analysis, primarily by augmenting accounts of conventional river flow series and historical descriptions. The epigraphic levels are converted into a discharge for inclusion within the flood frequency analysis. The conversion can be undertaken in one of two ways: The first involves constructing a rating curve consisting of simultaneous records from the epigraphic record and convention flow series.⁷ The second requires the calculation of the cross-sectional area of the channel and velocity measurements to produce an estimated discharge from the epigraphic level.⁸ The estimated discharges then can be incorporated within the flood frequency analysis.

As an integral tool in reconstructing extreme historical river flow records, epigraphic markings can improve our understanding of the frequency and magnitude of rare floods and ultimately of the mechanisms responsible for flood generation; in doing so, they provide an insight into periods of previous climatic variability, which may enhance understanding of current and future climatic changes.

Neil Macdonald is a lecturer in physical geography in the River Basin Dynamics and Hydrology Research Group at the University of Wales, Aberystwyth. His research focuses on the reconstruction of records and their application in reassessing trends and risks, to date predominantly focusing on hydrological and climatological data.

NOTES

^1. Alison Williams and David Archer, "The Use of Historical Flood Information in the English Midlands to Improve Risk Assessment," Hydrological Sciences Journal 47 (2002): 67–76; Neil Macdonald, "An Underutilized Resource: Historical Flood Chronologies a Valuable Resource in Determining Periods of Hydro-geomorphic Change," in IAHS/ICCE International Symposium on Sediment Dynamics and the Hydromorphology of Fluvial Systems, ed. John S. Rowan, Robert W. Duck, and Alan Werritty (Oxfordshire, England: IAHS Publ. 306): 120–27.

^2. Neil Macdonald et al., "Historical and Pooled Flood Frequency Analysis for the River Tay at Perth, Scotland," Area 38 (March 2006): 34–46; Alan Werritty et al., "Use of Proxy Flood Records to Improve Estimates of Flood Risk: Lower River Tay, Scotland," Catena 66 (2006): 107–19.

^3. Neil Macdonald, "The Application of Historical Flood Information in Reassessing Flood Frequency in Britain (Ph D diss., Department of Geography, University of Dundee, Scotland, 2004).

^4. On Perth, see Macdonald et al., "Historical and Pooled Flood Frequency Analysis"; on Nottingham, see Macdonald, "The Application of Historical Flood Information"; on Vallon, see Robin Naulet et al., "Flood Frequency Analysis on the Ardèche River Using French Documentary Sources from the Last Two Centuries," Journal of Hydrology 313 (November 2005): 58–78; on Cracow, see Jerzy Cyberski et al., "History of Floods on the River Vistula," Hydrological Sciences Journal 51 (October 2006): 799–817; and on Eibelstadt, see R. Brazdil et al., "Flood Events of Selected European Rivers in the Sixteenth Century," Climatic Change 43 (1999): 239–85.

^5. Annual Register (1771), vol 14. Chronicle pp. 155–56.

^6. Georgina H. Endfield, Isabel Fernández Tejedo, and Sarah L. O'Hara, "Conflict and Cooperation: Water, Floods, and Social Response in Colonial Guanajuato, Mexico," Environmental History 9 (April 2004): 221–47.

^7. Macdonald et al., "Historical and Pooled Flood Frequency Analysis."

^8. Macdonald, "The Application of Historical Flood Information."

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