Lateral extent • Elevation change • Changes in creek and marsh • Changes in floristic composition • Changes in vegetation vigour

Lateral extent

Although saltmarsh erosion is the most widely perceived problem, expansion of saltmarsh can also cause environmental management problems, most notably when it leads to enhanced estuarine siltation and navigation difficulties, or deterioration in the quality of amenity beaches. For example, colonisation of formerly sandy beaches at Southport and south of Cleethorpes has posed significant problems for the local authority in terms of tourism appeal and bathing water quality.

Short to medium term trends in marsh edge progradation or retreat can often be inferred by examination of the marsh edge morphology. Accreting and stable marsh edges are usually typified by an accretional ramp upon which pioneer and low-marsh vegetation communities become stabilised (A and B in Figure below). Erosional margins, on the other hand, are characterised either by the presence of mud-mound topography or by marsh-edge cliffs fronted by toppled blocks (C and D). Terraced marsh margins (E) indicate episodic erosion and accretion on timescales of decades and centuries.

Marsh edge morphology types, after Pye and French (1993)

Quantitative data on rates of marsh edge retreat can be obtained from comparison of Ordnance Survey maps, Admiralty charts, air photographs or ground surveys of different dates (e.g. van der Wal and Pye, 2004; and Figure below).

Changes in the position of the saltmarsh edge along the Dengie Peninsula, Essex, between 1955 and 1990, based on Ordnance Survey maps and aerial photographs (after Pye and French, 1993)