Secondary flows and the pool‐riffle unit: A case study of the processes of meander development

Abstract

AbstractThe major bedforms of gravel bed rivers, whether braided, meandering or straight, may be usefully resolved into pool‐riffle units, each comprising a single scour pool together with an associated depositional shoal downstream. At low flow, the latter may be characterized by a single emergent bar‐head and submerged riffle, or by a variety of remnant braid bars, depending upon the type of channel.Identification of pool‐riffle units and observation of associated flow structures on a small meandering stream in northwest England has demonstrated important links between bedforms, flow patterns and channel change.Each unit appears to be associated with a systematic pattern of secondary flows, which are able to modify the bedforms and initiate meander development. Feedback links between plan morphology, flow patterns and erosive and depositional forces within these units ensure that each stage of meander growth has a characteristic style of channel change. Consequently, meanders tend to evolve by regular cycles of increasing curvature and complexity.