Sedimentation in the meandering River Endrick

Abstract

The River Endrick carries gravel and finer sediment in a pool and riffle channel. Point bars and riffles, which alternate along most of the channel, are foci of active particle-size segregation within the general downstream size decline: they are therefore centres of facies change. This differentiation results in sediment of a particular size being systematically and repeatedly placed in similar parts of the channel: on point bars, for example, proportionately more gravel is found at the apex and more sand in the cross-over reaches of the meander. Cross-stratal dip direction in these sediments is roughly parallel to the local flow and is therefore different in sand and gravels. It also follows that sand has a higher standard deviation of cross-bed dip orientation than gravel. The bed forms of the river often have only a superficial thickness of related sediment: they were built by a lower stage of flow than most of the sediment enclosed by the form, and in this sense forms give an erroneous measure of structure.