The American model SLAMM was used to evaluate long-term stability of salt marshes in Friesland and Groningen for various scenarios of sea level rise and accretion rate. On both locations, salt marshes are more resilient to sea level rise than to low accretion rates.
Rising sea levels increase coastal flood risks. Wave attenuation by salt marshes is able to reduce flood risks. Salt marshes are able to keep up with sea level rise to some extent thanks to vertical accretion; lateral retreat is not possible due to dikes. Most research on salt marshes focusses on quantification of wave attenuation, but here the long-term stability of salt marshes is assessed. SLAMM (Sea Level Affecting Marshes Model) is used to evaluate long-term stability of a typical salt marsh transect in Friesland and Groningen until the year 2100. The model uses a DEM, a slope file and a vegetation category class file as input. Parameterization of SLAMM is based on elevation change measurements from 2001 until 2010, a DEM from 2007-2009 and vegetation mapping by Rijkswaterstaat in 2008. Results show that accretion rates as a function of elevation have a large variation, which makes parameterization more complex. Sensitivity analyses with various scenarios of sea level rise, accretion rates and initial bed profile indicate that salt marshes in Groningen are more vulnerable than in Friesland. Salt marshes on both locations are more resilient to sea level rise than to a limited sediment supply. SLAMM is an American model, originally created to evaluate the ability of drowning marshes to keep up with various scenarios of sea level rise. Modelling of growing marshes, as is the case in Friesland and Groningen due to high accretion rates, therefore has its shortcomings.