Contemporary sediment dynamics and Holocene evolution of Hamford Water, Essex, England
Contemporary sediment transport, suspended sediment flux, rates of intertidal sedimentation, and Holocene sedimentation history are assessed for Hamford Water, a small meso-tidal inlet and saltmarsh embayment in Essex, UK. Sediment transport rates are calculated using semi-empirical equations; suspended sediment flux is computed by integration of suspended sediment concentration and velocity across the inlet throat; intertidal sedimentation rates are assessed from monitoring of discrete markers on saltmarsh and mudflat; and Holocene sedimentation is estimated from radiocarbon dating of buried organic layers, sampled using a vibrocorer. Results show a tidal regime typical of ebb-dominated inlets: moderate, ebb-dominant flow (==1 m S·l) in the central ebb channel is matched by similar flood-dominant marginal channel flows. The sediment dynamics are not influenced by any fluvial input; there is negligible fresh water input. The net direction of sediment transport is predominantly ebb-orientated. Coarse sand transport pathways are circulatory and dependent on longshore drift. Sand (D = 0.25 mm) enters at the margins and is expelled in the central ebb channel. Negligible sand is transported further landward than the mouth; intertidal sedimentation relies mainly on levels of suspended sediment. Rates of intertidal sedimentation are spatially variable: tidal creek sedimentation is greater than saltmarsh, with a mean rate of 4.2mm yr"l. Buried organic horizons. radiocarbon dated to 600 years BP, are attributed to reclaimed land levels. Holocene sedimentation rates since 4300 years BP, estimated from 14C dating of shell bands. accord with current estimates of sea-level rise of approximately 1 mm i 1 • The role and evolution of the inlet entrance and ebb tidal delta are seen as critical to the evolution of the embayment as a whole. The interaction of the embayment with the adjacent coastal zone considered essential when fonnulating shoreline management plans. Hamford Water is considered an integral part of the Stour/OrwelllNaze coastal system.