Sedimentological controls on the erosion and morphology of saltmarshes: implications for flood defence and habitat recreation

The factors which influence the morphology, drainage characteristics and erosion resistance of saltmarshes are of major interest from the standpoint of flood defence and habitat recreation. Sedimentological characteristics, including grain size distribution, mineral composition and pore fluid chemistry are all highly important. Of particular importance in muddy marshes is the nature of the clay mineral assemblage and dissolved cations present in the pore fluids. In marshes which are deficient in detrital calcium carbonate, such as those in Essex, UK, sodium ions dominate the exchange sites on clays, leading to the formation of thick water films around the clay particles and slow rates of sediment consolidation. This, in turn, causes low erosion resistance and a tendency for the development of highly dissected marsh morphology. Calcium and magnesium-rich marsh sediments, on the other hand, allow these ions to replace sodium in exchange sites, leading to more rapid dewatering and consolidation. Erosion resistance is thereby enhanced and such marshes tend to be characterized by low drainage densities and a low ratio of bare mud to vegetated surface area. The possibilty of engineering the erosion resistance and morphology of marshes through chemical treatments requires further investigation.