Is wind-wave fetch exposure related to soft shoreline change in swell-sheltered situations with low terrestrial sediment input?

Rising sea levels and changing wind climates are widely expected to be associated with receding coastlines, creating a planning need for coastal change prediction, especially for soft shores like those associated with saltmarsh. We ask whether it is possible use a simple cartographic wind-wave fetch method to estimate the spatial pattern of progradation and recession of soft shores in swell-sheltered situations in which there is little or no input of new sediment from terrestrial sources. For points on an extensive embayment shoreline of this type we mapped change over 54 years from aerial photographs, recorded current shoreline morphology and calculated a wave fetch index (WFI). Morphological indication of strong progradation was associated with low WFI, but there was no statistically significant effect of variation in WFI on the degree of shoreline retreat. Saltmarsh shorelines averaged 14 cm per annum retreat between 1952 and 2006, a rate that did not vary significantly between air photo periods. We conclude that our geographic information system approach utilising WFI is likely to be useful as a planning tool in identifying those parts of sediment-poor saltmarsh shores where erosion is most likely or least likely to occur, but not particularly useful for predicting finer-scale variation in rates of shoreline recession within the particular substrate types in our study area. In the context of relative sea-level rise and increasing wind speeds, such modelling can help identify coastlines which are likely to support saltmarshes into the future.