Conclusions
This chapter reports initial attempts to estimate accretion rates across a large area of
vegetated saltmarsh. Although there are significant uncertainties about the approach,
there appear to be few practical alternatives. To rely on digging up markers as in the
experiment reported by Steers (1960), introduces problems with extrapolating net
accretion due to the steady loss of sites. Attempts to use ground survey to describe the
shape of the surface to the required degree of accuracy (to within a millimetre) implies
very high costs as well as the practical problem of deciding exactly where the surface
of wet mud is. These initial findings will help to quantify the flux of materials between
the land and the ocean and help to assess the impacts of pressing environmental
problems such as sea-level rise.
Acknowledgements
This work was funded under the NERC Land Ocean Interaction Study. We wish to
thank the National Rivers Authority (now the Environment Agency) for access to their
transect information. We would also like to thank: Jim Eastwood , Robin Fuller & Tim
Sparks for help with analysis of the imagery and Laurie Boorman & Selwyn McGrorty
for help with collecting data on the ground (or rather mud!).
References
Brown, N.J., Cox R., Pakeman, R., Thomson, A.G., Wadsworth, R.A., and Yates, M.
(1997). Development of a spatial decision support system for the BIOTA
project within LOIS. Proceedings CoastGIS’97 Aberdeen
August
1997
244
N.J. Brown et al.
Constructing a DTM from filtering an interpolated surface by ground cover
provides a certain amount of circularity in the argument. In addition, problems with
geo-referencing the image and the way in which the profiles record every creek mean
that there is an unknown uncertainty with the final predicted elevations. The method
for identifying creeks is possibly deficient and will lead to underestimates of deposition
away from the front edge of the marsh.
One of the most difficult parameters to estimate is the concentration of
sediment in the water column, and how much of it represents "new" sediment and how
much is being transported around on the local scale.
The Admiralty method of predicting tidal levels is designed for particular
ports, the physical characteristics of many parts of the coast are likely to lead to rather
different tidal behaviour. Use of a hydrodynamic model which takes into account the
bathymetry would be preferable.
Basing long term predictions from short term observations are likely to lead to
compounded errors. In particular the importance of occasional rare events is
impossible to capture in such an approach.
This chapter reports initial attempts to estimate accretion rates across a large area of
vegetated saltmarsh. Although there are significant uncertainties about the approach,
there appear to be few practical alternatives. To rely on digging up markers as in the
experiment reported by Steers (1960), introduces problems with extrapolating net
accretion due to the steady loss of sites. Attempts to use ground survey to describe the
shape of the surface to the required degree of accuracy (to within a millimetre) implies
very high costs as well as the practical problem of deciding exactly where the surface
of wet mud is. These initial findings will help to quantify the flux of materials between
the land and the ocean and help to assess the impacts of pressing environmental
problems such as sea-level rise.
Acknowledgements
This work was funded under the NERC Land Ocean Interaction Study. We wish to
thank the National Rivers Authority (now the Environment Agency) for access to their
transect information. We would also like to thank: Jim Eastwood , Robin Fuller & Tim
Sparks for help with analysis of the imagery and Laurie Boorman & Selwyn McGrorty
for help with collecting data on the ground (or rather mud!).
References
Brown, N.J., Cox R., Pakeman, R., Thomson, A.G., Wadsworth, R.A., and Yates, M.
(1997). Development of a spatial decision support system for the BIOTA
project within LOIS. Proceedings CoastGIS’97 Aberdeen
August
1997
244
N.J. Brown et al.
Constructing a DTM from filtering an interpolated surface by ground cover
provides a certain amount of circularity in the argument. In addition, problems with
geo-referencing the image and the way in which the profiles record every creek mean
that there is an unknown uncertainty with the final predicted elevations. The method
for identifying creeks is possibly deficient and will lead to underestimates of deposition
away from the front edge of the marsh.
One of the most difficult parameters to estimate is the concentration of
sediment in the water column, and how much of it represents "new" sediment and how
much is being transported around on the local scale.
The Admiralty method of predicting tidal levels is designed for particular
ports, the physical characteristics of many parts of the coast are likely to lead to rather
different tidal behaviour. Use of a hydrodynamic model which takes into account the
bathymetry would be preferable.
Basing long term predictions from short term observations are likely to lead to
compounded errors. In particular the importance of occasional rare events is
impossible to capture in such an approach.