Sedimentary model for intertidal mudflat channels, with examples from the Solway Firth, Scotland

Abstract

ABSTRACT Intertidal mudflat channels (gullies) in the Solway Firth, Scotland possess width/depth ratios similar to meandering rivers. Most channels deeper than 1 m show cut‐bank slides, but narrow, deep channels also have rotational slides on the point‐bar slopes. The channels display two types of point‐bar. The first, associated with gently curved meanders, is sigmoidal in profile. The second, associated with tight meander bends, possesses a pronounced lower platform. The onset of flow separation in meander bends, a phenomenon which enhances cut‐bank erosion and point‐bar deposition, is a direct function of meander‐bend tightness and Froude number. The effects of flow separation are greatest on tight meander bends at times of high velocity during late spring ebb and also during rainfall run‐off at low tide. These events appear to be responsible for the growth of the point‐bar platforms. A model, predicting the type of point‐bar development to be expected in different channel meanders, is used to reconstruct the sedimentary history of active and fossil point‐bars.