A geomorphological interpretation of saltmarsh channel network morphology and function
Although tidal channel networks are a near-ubiquitous feature of saltmarsh environments developed on the marine sedimentary shores of Britain, only limited progress has been made towards achieving a scientific understanding of their morphological characteristics and the physical functions that they perform. Based on data acquired from a combination of high resolution aerial photography and field survey, a range of descriptive indices and morphometric measures are used to characterise planimetric, longitudinal and cross-sectional adjustment in saltmarsh channel networks from 29 localities around England and Wales. In accordance with the extensive methodological approach employed during this exploratory phase of the study, regularities and distinguishing features of the selected formations are interpreted in terms of broad-scale environmental controls, which represent the relative intensity of erosional versus resistive forces. While statistical analyses suggest that creek morphology reflects a multiplicity of influences, the strongest bivariate associations, between tidal prism and cross-sectional geometry, are consistent with the finding of earlier process studies that creek morphology is principally adapted to perform a conveyance function. Theoretically-based mathematical models are employed to more fully elucidate relations of causality between creek morphology and function. This intensive investigation utilises Brancaster Marsh, Norfolk as an illustrative case study. The availability of airborne laser altimetry (lidar) for this site facilitates the evaluation of alternative models of channel function. Optimality models of angular geometry are implemented at a network-scale, and cross-sectional adjustments are modelled with reference to the concept of stability shear stress. While of interest from a geomorphological perspective, the insights offered into creek morphology and function are also relevant to the field of coastal engineering. Here, they provide an empirical basis for post-project appraisal, and may lead to theoretical guidelines for the design of tidal channel networks, as an integral component of saltmarsh restoration and flood defence realignment schemes.