The influence of recent environmental change on flooding and sediment fluxes in the Yorkshire Ouse basin

Abstract

This study attempts to establish causes of historical variations in¯ood frequency and magnitude in a 119-year ood stage record at York, and assess its likely eects on¯uxes of ®ne sediment and associated base metal contaminants. Climatic controls of¯ooding are evaluated through analysis of synoptic¯ood generation, and large-scale land use changes are also considered in terms of their in¯uence on food frequency and magnitude and sediment availability. The late nineteenth century was characterized by low¯ood frequency and magnitude, but, as a consequence of upland metal mining, contaminant concentrations and downstream ®ne sediment delivery would have been high. A further decline in¯ood frequency and magnitude between 1904 and 1943, combined with the cessation of base metal mining, resulted in a decline of sediment and contaminant¯uxes. Between 1944 and 1968 increases in upland drainage, changes in agricultural practices and high¯ood frequency and magnitude resulted in signi®cantly enhanced sediment¯uxes. Rates of¯ux declined between 1969 and 1977 owing to extremely low¯ood frequencies and magnitudes. In the last two decades there have been a series of extreme magnitude¯oods, 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 ood frequency and magnitude in the UK, and signi®cantly enhanced sediment and contaminant metal¯ux. Analysis of synoptic¯ood generation suggests that any future increase in the frequency and vigour of cyclonic atmospheric circulations may result in a higher frequency of extreme¯oods and consequently increased sediment¯uxes.

Explanatory analysis of the relationship between atmospheric circulation and occurrence of flood-generating events in a coastal city

“…The unclassified type (U) was not observed during the studied period. These results are in accordance with LCT frequencies assessed in previous studies for UK (Longfield and Macklin, 1999;Pattison and Lane, 2012) and Sweden (Chen, 2000). LCC A is similarly dominant with over 30%, and LCCs W and C have very similar frequencies.…”

Alluvial responses to the changing Earth system

“…The increase in flooding recorded in Yorkshire Ouse catchment since the 1980s (Longfield and Macklin, 1999) is also evident in other parts of northern (Werritty, 2002) and western Britain (Higgs, 1987). In the upper Severn basin, mid-Wales, for example, increased flooding has resulted in higher bank erosion rates and larger areas of gravel within the channel, stored within periodically mobile gravel-bar complexes (Gittins, 2004).…”

Incorporating sedimentological data in UK flood frequency estimation

“…Typically, flood frequency estimates (also known as design flood estimates) are derived by fitting statistical models to a series of annual maximum (AMAX) peak flows measured at a gauging station. There are a small number of AMAX records that have more than a century of data (see Longfield & Macklin, 1999;Marsh & Harvey, 2012); however, for most locations the gauged record is relatively short (most begin between 1950 and 1980), often much shorter than the rarity of events required for design of flood defences and reservoir spillways, ranging from 100 to 10,000 years. To overcome this, current methods in FEH advocate the "pooling" of data from hydrologically similar sites, but ideally flood estimates would be based on a long data series representing the flood characteristics at the location of interest.…”