TIDAL MARSH SEDIMENTATION VERSUS SEA-LEVEL RISE: A SOUTHEASTENGLAND ESTUARINE PERSPECTIVE

摘要

Tidally dominated marshes typically exhibit rates of sedimentation which exceedrncontemporary sea-level rise and modelling studies have demonstrated the tendency of theirrnelevations to track moderately accelerated rates of sea-level rise. In southeast England, however,rnerosion of the intertidal zone over the last few decades has greatly reduced the area of estuarinernsaltmarsh. Rates of vertical accretion thus represent only one aspect of morphodynamic adjustmentrnand marsh sedimentary performance must be evaluated against a wider geomorphic context. Thisrnpaper examines these issues with reference to a case study of the Blyth estuary, Suffolk, wherernbreaching and inundation of mid-estuary reclamations in the 1920s - 1940s has created extensivernlow-lying tidal flats which subject to intermittently strong wave action. Adjustment of salt marshrnelevations, quantified through precise monitoring of short-term elevation change and estimation ofrnmedium-term sedimentation, is evaluated against historical changes in marsh area and a conceptualrnmodel of estuary morphodynamics. Vertical sedimentation over 5 and 40 year time scales easilyrnoutpaces a post-1964 sea-level rise of 2.4 mm arna-1 -1. Analysis of historical planforms reveals a smallrnincrease in saltmarsh area since 1887, largely due to localised re-establishment of marshes withinrnparts of the abandoned reclamations. A more detailed pattern of spatially- and temporally-varyingrnfoci of marsh erosion and accretion appears to be more obviously linked to changes in a larger-scalernestuary process regime shaped by a combination of dredging, reclamation and partial abandonmentrnthan to external sea-level rise forcing.rn.