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



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.