Assessing the relation between the distribution of salt-marsh communities and the sediment budget of the North Norfolk coast

Abstract

Very high resolution imagery from an airborne multi-spectral scanner has been used to estimate the distribu- tion of different salt-marsh communities along a 30-km stretch of the North Norfolk coast. Field observations have been used to develop a mathematical relationship between the vegeta- tion, physical environment and sediment accumulation. This relationship has been used to produce provisional sediment accretion maps for the North Norfolk coast. Structure of the model A mathematical model based on the analysis of field data has been constructed to estimate the rate at which sediment accumulates on a salt marsh. The model has been designed to fit within the SDSS framework to allow a variety of users to investigate the sensitivity of the assumptions made and to inves- tigate the possible effects of sea level rise. Analysis of field observations was carried out using stepwise linear regression for a variety of vegetation types independently. In each case the depth of sediment accumulated on a single tide was found to be signifi- cantly positively correlated with the length of time an area is submerged and the amount of sediment in the water and negatively correlated with distance from the nearest creek and the density of the sediment. These individual equations were then combined to give the form shown below. Considering accumula- tion per unit time the vegetation coefficient (v) can be shown to have units of area. This implies that, all other things being equal, species with a large or complex cross-sectional area trap sediment more ef- ficiently than smaller or less complex species. The final form of the model is: