WAVE TRANSFORMATIONS OVER MUDFLAT AND SALTMARSH SURFACES ONTHE UK EAST COAST - IMPLICATIONS FOR MARSH EVOLUTION

摘要

An extensive dataset of wave spectra was collected for marsh surface inundationrnevents (Sept 2000 - Jan 2002) at two sites on the Dengie saltmarshes, eastern England (southernrnNorth Sea), using a network of 21 bottom-mounted pressure sensors, covering both intertidalrnmudflat and saltmarsh surfaces. This paper focuses on an in-depth analysis of changes in wavernspectra over a range of distances across mudflat and saltmarsh surfaces and at a cliffed marshrnedge during 15 selected inundation events. Directional wave spectra were obtained on thernunvegetated intertidal flat and, together with information on meteorological conditions, are usedrnto explain the temporal and spatial variations in wave spectral characteristics. In particular, thernobserved patterns / re-distribution of spectral energy and peak wave period shifts over thernmudflat and the marsh surface are discussed for contrasting root-mean-square wave heightrn(Hrms) to water depth (h) ratios. Similarities and differences in the spectral transformationsrnobserved at both sites are discussed with reference to the contrasting mudflat and marsh edgerntopographies of the two field sites. From this comparison, the paper concludes that siterncharacteristics, including substrate type, micro-topography, and marsh surface vegetation cover,rnrather than meteorological conditions, are crucial in explaining the wave spectra transformations.rnSpectral transformations at the gradually sloping mudflat-saltmarsh transition generally confirmrnexpected patterns of energy redistribution derived from wave theory and observed in laboratoryrnmodels. At the more complex, cliffed transition, however, spectral changes vary significantlyrnbetween events with contrasting ('high' vs. 'low') Hrms/h ratios. Improved models are nowrnrequired to (a) evaluate marsh surface responses to changes in environmental forcing consequentrnupon global climate change, and (b) assist in the formulation of 'design rules' for the restorationrnand re-creation of degrading marsh systems.