Tracing sources of suspended sediment in river basins: A case study of the River Culm, Devon, UK

Information on the source of the suspended sediment transported by a river is becoming an increasingly important requirement in sediment investigations. Such information is difficult to assemble by means of traditional monitoring strategies, but the 'fingerprinting' technique offers considerable potential. The use of composite 'fingerprints' in combination with a multivariate mixing model can provide a basis for determining the relative importance of both individual areas of a catchment and specific source types. The results of applying this approach to the 276-km² basin of the River Culm in Devon, UK are presented. A suite of nine fingerprint properties was employed as a composite fingerprint, and this permitted the relative contributions of seven source types to be established. These source types represented material derived from the surface af cultivated and pasture areas on each of the three main rock types and material eroded from channel banks. By collecting samples of suspended sediment at different times during individual floods, it was possible to document changes in the relative contributions of the various sources during each flood in response to runoff source and travel times. Although the multivariate fingerprint approach has a number of limitations, it also has considerable potential as a means of tracing sources of suspended sediment within a large drainage basin.