River sedimentation and fluvial response to Holocene environmental change in the Yorkshire Ouse Basin, northern England

Holocene alluvial sediment sequences and floodplain geomorphological histories from three valley-floor sequences in the Yorkshire Ouse Basin have been determined using a variety of field evidence and laboratory methods: geomorphological mapping, sediment coring and trenching, physical and chemical analysis of sedimentary units, and ¹⁴C dating. The application of multiple methods has revealed contrasting phases of fiver erosion, alluviation and depositional styles during the Late Quaternary at each of the individual study reaches. The gravel-bedded River Swale at Catterick has been characterized by progressive valley-floor incision during the late Holocene with major phases of incision occurring during the cooler and wetter phase of the 'Little Ice Age'. Within the last c. 245 years, substantial thicknesses (up to 2 m) of overbank alluvium contaminated by metalliferous mining have been deposited across the floodplain. In contrast, floodplain development in the lower reaches of the River Swale at Myton and the River Aire at Beal has predominantly been one of relative channel stability and vertical aggradation. Here, low floodplain gradients, wide valley floors, stable channels and limited lateral floodplain erosion have combined to produce thick (c. 10 m) sequences of fine-grained alluvium deposited in overbank environments. Mining-related contamination in lowland floodplains is much lower than at Catterick with limited amounts of historically contaminated alluvium being deposited across the floodplain. Although environmental change has been important in controlling Holocene floodplain development, the upper and lower reaches of the Yorkshire Ouse basin have responded differently to these effects because of reach-scale geomorphic controls. Caution needs to be applied before relating broad-scale environmental change to river response across a whole fiver basin.