Fingerprinting suspended sediment sources in the catchment of the River Ouse, Yorkshire, UK

Statistically verified composite fingerprints and a multivariate mixing mod el have been employed to establish the main sources of the suspended sedime nt transported through the lower, non-tidal reaches of the River Ouse and o ne of its main tributaries, the River Wharfe, during the period 1994-1997. In the case of the suspended sediment samples collected from the River Ouse , the load-weighted mean contributions from uncultivated topsoil, cultivate d topsoil and channel bank sources were estimated to be c. 25, 38 and 37%, respectively, while for the River Wharfe these sources contributed c. 70, 4 and 23%, respectively (c. 4% was derived from woodland topsoil). Suspended sediment samples collected during higher flows evidenced a greater contrib ution from channel banks than samples collected during lower flows. Source materials were also differentiated according to the three main geological s ource areas (Carboniferous, Permian and Triassic, and Jurassic) and their l oad-weighted mean contributions were estimated to be c. 24, 41 and 35% for the River Ouse and c. 91, 9 and 0% (there are no Jurassic rocks in this cat chment) for the River Wharfe, respectively. When suspended sediment samples from tributary streams were used to characterize each geological source ar ea, the equivalent results for the River Ouse were c. 30, 46 and 24%. Consi dering the three main tributaries that contribute to the River Ouse, the lo ad-weighted mean contributions from the rivers Swale, Ure and Nidd were est imated to be 82, 15 and 3%, respectively. These values have been compared w ith estimates of the relative magnitude of the annual suspended sediment lo ads of these three rivers for the years 1995 and 1996 derived from continuo us monitoring of discharge and turbidity. Differences between the two sets of results are ascribed to the different periods of record involved and to the timing of suspended sediment sampling relative to the overall storm hyd rograph, and thus the degree to which the available samples are representat ive of the overall suspended sediment flux. Although a number of limitation s must be recognized, the fingerprinting approach to source ascription is s een as providing valuable information regarding suspended sediment sources in the study catchments. Copyright (C) 1999 John Wiley & Sons, Ltd.