Wave height • Water depth • Width & edge characteristics • Topography & bed friction • Vegetation density

Vegetation density

The extent of wave attenuation across saltmarsh areas is also influenced by the nature and density of the saltmarsh vegetation. Differences can be due to spatial variability in vegetation density, the species composition and seasonal variability in the vegetation characteristics.

The area of saltmarsh immediately landward of the permanently vegetated edge is most significant in terms of attenuating wave energy, so vegetation changes in this area are likely to have the greatest influence. Möller and Spencer (2002) observed a correlation between lowered wave attenuation and seasonal decreases in vegetation density over a gradually sloping saltmarsh edge. The same study observed no such relationship over a steep cliffed saltmarsh margin, suggesting that the dominant effect on wave dissipation at this type of site is the cliffed topography rather than the vegetation.

The vegetation community type can also influence wave attenuation rates, due to the different physical structure of the plants. Across Dengie, Möller et al. (1999) identified a possible link between vegetation density, wave attenuation and the type of vegetation, with the flexible grass Puccinellia spp. in the upper saltmarsh having less effect on wave attenuation than the saltmarsh dominated by Salicornia and Suaeda spp.