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

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.

Ecohydrology as a new tool for sustainable management of estuaries and coastal waters

“…Saltmarsh accretion via creek processes considers the incoming sediment-laden waters to be funnelled by the creek network, which then overspill once the altitude of the fringing saltmarsh is exceeded. In this example, sedimentation is focused in the immediate vicinity on the creek margins in the form of levees, and vertical accretion is achieved by lateral creek migration over the long term (Bridges and Leeder 1977). Providing that the saltmarsh is not limited by an insufficient supply of sediment or spatially constrained by levees preventing its landward movement, a saltmarsh can respond to sea-level rise via an landward retreat and/or enhanced sediment accretion.…”

Coastal Salt Marshes

“…Channel erosion on bare tidal flats essentially takes place in response to three mechanisms: (1) direct, fluid shear stress against the substrate; (2) action of smallscale waves (wavelets) against channel banks; and (3) rotational slides (Reineck, 1970;Laury, 1971;Bridges and Leeder, 1976). On vegetated flats, similar processes act on channels; but bank undercutting and subsequent slumping and rotational sliding of coherent (root-bound) blocks may become a relatively more important factor than on some unvegetated flats.…”

Meandering channel dynamics in highly cohesive sediment on an intertidal mud flat in the Westerschelde estuary, the Netherlands

“…Unvegetated intertidal mudflats and vegetated tidal salt marshes commonly have small meandering channels (e.g., Bridges and Leeder, 1976;Gabet, 1998;Fagherazzi and Furbish, 2001;Temmerman et al, 2003b). Sediment on mudflats is generally very strong compared to the bank and bed sediment of terrestrial rivers even where the banks of the latter consist of cohesive sediment and are vegetated.…”