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Extreme floods are the most widespread and often the most fatal type of natural hazard experienced in Europe, particularly in upland and mountainous areas. These ‘flash flood’ type events are particularly dangerous because extreme rainfall totals in a short space of time can lead to very high flow velocities and little or no time for flood warning. Given the danger posed by extreme floods, there are concerns that catastrophic hydrometeorological events could become more frequent in a warming world. However, analysis of longer term flood frequency is often limited by the use of short instrumental flow records (last 30–40 years) that do not adequately cover alternating flood-rich and flood-poor periods over the last 2 to 3 centuries. In contrast, this research extends the upland flood series of South West England (Dartmoor) back to ca AD 1800 using lichenometry. Results show that the period 1820 to mid-1940s was characterized by widespread flooding, with particularly large and frequent events in the mid-to-late 19th and early 20th centuries. Since ca 1850 to 1900, there has been a general decline in flood magnitude that was particularly marked after the 1930s/mid-1940s. Local meteorological records show that: (1) historical flood-rich periods on Dartmoor were associated with high annual, seasonal and daily rainfall totals in the last quarter of the 19th century and between 1910 and 1946, related to sub-decadal variability of the North Atlantic Oscillation and receipt of cyclonic and southerly weather types over the southwest peninsula; and (2) the incidence of heavy daily rainfall declined notably after 1946, similar to sedimentary archives of flooding. The peak period of flooding on Dartmoor predates the beginning of gauged flow records, which has practical implications for understanding and managing flood risk on rivers that drain Dartmoor. Copyright © 2013 John Wiley & Sons, Ltd.

Lewin, J., Macklin, M. G. (2010). Floodplain catastrophes in the UK Holocene: messages for managing climate change. Hydrological Processes, 24(20), 2900-2911.

Gregory, K. J., Benito, G., Dikau, R., Golosov, V., Johnstone, E. C., Jones, J. A. A., Macklin, Mark G., Parsons, A. J., Passmore, D. G., Poesen, J., Soja, R., Starkel, L., Thorndydraft, V. R., Walling, D. E. (2006). Past hydrological events and global change. 20: 199-204.

During the autumn of 2000, large areas of England and Wales were affected by severe flooding, which caused widespread disruption and significant damage to property. This study attempts to determine the impact of these flood events on contaminated sediment dispersal and deposition in the River Swale catchment, Yorkshire, UK, where lead and zinc were extracted and processed in large quantities during the nineteenth century. Seventy samples of overbank and channel-edge sediments were collected at 35 sites along the River Swale. Inductively coupled plasma-mass spectrometry was used to measure contaminant metal concentrations in the 2000–63 µm (sand) and

In the UK's upland catchments river terraces and alluvial features indicate a history of periodic aggradation and degradation linked to Holocene changes in land use (primarily deforestation) and climate change (altering flood frequency and magnitude). Although both factors are important, calculating their individual effects is complicated by the likelihood of their concurrent alteration. To investigate the relative impacts of land use and climate change, a cellular model is applied to the upland catchments of Cam Gill Beck, above Starbotton, North Yorkshire. This is divided into 1 million 2 m by 2 m grid cells, to which a range of process laws are applied. These include approximate expressions for mass movement rates, soil creep, the influence of vegetation and hillslope hydrology, as well as fluvial erosion and deposition in ten grain-size fractions. This provides a good representation of valley floor geometry while retaining a fully dynamic interaction with the surrounding valley sides. Previous applications of this model have shown the detailed formation of bars and berms as well as examples of braiding, avulsion and channel range. Running on a Silicon Graphics Origin 2000 computer, an ensemble of simulations were completed, bracketing a wide range of environmental scenarios involving changes in flood frequency, magnitude and vegetation cover. Over time-scales ranging from 10 to 100 years, these showed that decreasing tree cover and increasing rainfall magnitude individually produced similar 25% to 100% increases in sediment discharge, whereas in combination they generated a 1300% rise. Furthermore, channels formed by the model in response to increased rainfall magnitudes are located where relic channels are found in Cam Gill Beck, implying that these are the products of previous periods of high rainfall magnitudes. Copyright © 2000 John Wiley & Sons, Ltd.

This study attempts to establish causes of historical variations in flood frequency and magnitude in a 119-year flood stage record at York, and assess its likely effects on fluxes of fine sediment and associated base metal contaminants. Climatic controls of flooding are evaluated through analysis of synoptic flood generation, and large-scale land use changes are also considered in terms of their influence on food frequency and magnitude and sediment availability. The late nineteenth century was characterized by low flood frequency and magnitude, but, as a consequence of upland metal mining, contaminant concentrations and downstream fine sediment delivery would have been high. A further decline in flood frequency and magnitude between 1904 and 1943, combined with the cessation of base metal mining, resulted in a decline of sediment and contaminant fluxes. Between 1944 and 1968 increases in upland drainage, changes in agricultural practices and high flood frequency and magnitude resulted in significantly enhanced sediment fluxes. Rates of flux declined between 1969 and 1977 owing to extremely low flood frequencies and magnitudes. In the last two decades there have been a series of extreme magnitude floods, which through remobilization of mining-contaminated alluvium have resulted in high pollutant metal mining loads, probably approaching those of the late nineteenth century. In an historical context it appears that the LOIS monitoring programme has been undertaken in a period of extremely high flood frequency and magnitude in the UK, and significantly enhanced sediment and contaminant metal flux. Analysis of synoptic flood generation suggests that any future increase in the frequency and vigour of cyclonic atmospheric circulations may result in a higher frequency of extreme floods and consequently increased sediment fluxes.

Floodplain overbank sediments are often used to evaluate the influence of environmental change on sediment and chemical fluxes within river basins. This paper presents the results of an investigation of heavy metal storage in seven floodplain reaches in the Yorkshire Ouse basin in north-east England. Floodplain heavy metal storage has been greatest since c. 1750, and many of the post-1750 sedimentary units exhibit heavy metal values that exceed recommended trigger and guideline values for contaminated land. Relatively high heavy metal storage occurs from ad 1250–1750 in most of the reaches. These patterns are related to 2000 years of Pb and Zn mining in the Yorkshire Dales and c. 250–300 years of industrial and urbanization activity around Leeds and Bradford, and increased delivery of fine-grained sediment during the last millennium, possibly owing to factors such as population growth and agricultural expansion during the Middle Ages, and climate change during the Little Ice Age. Copyright © 1999 John Wiley & Sons, Ltd.

Concentrations of heavy metals (Cd, Cu, Pb and Zn) on suspended sediments during a flood event at Thwaite Mills, River Aire, were analysed using a five step sequential extraction technique to determine their major chemical associations (exchangeable, surface oxide and carbonate, Fe and Mn oxides, organic and residual metal ions). Total metal concentrations were lowest at higher discharges, resulting from dilution by clean sediment. The major transport fractions are the Fe and Mn oxides, which carry 29% of the total metals. Knowledge of the chemical forms of heavy metals on suspended sediment is essential for estimating their biological availability and physicochemical reactivity. © 1998 John Wiley & Sons, Ltd.