Distance from the nearest creek
The distance from the nearest creek has been estimated by reclassifying the image to
try and identify creeks and then apply a buffer around them. Note, however, that even a
resolution of five meters is rather coarse for the complex topography of the typical salt
marsh, this may explain why the mean distance to a creek (80 meters) appears rather
high by this method.
The Effect of Saltmarshes on Sediment Deposition
237
profile information with the CASI imagery the relationship between the shape and
stability of the beach and the vegetation can be revealed.
Fig. 2 shows a profile across Scolt Head Island. Note the dunes and shingle
ridges protecting the salt marsh, and the stability of the profile over a three year period.
Fig. 3 shows a more exposed profile one kilometre to the east of the town of Wells
where a single minor ridge is sufficient to protect stable salt marsh vegetation this is,
however, conspicuously different from that at Scolt Head Island. Fig. 4 shows a profile
mid way between Wells and Blakeney Point where the vegetation is very similar to the
Scolt Head profile, however, the bare sediment is much more dynamic than the in the
other two profiles.
It is interesting to observe the very narrow and consistent range of elevations
within which the different species exist and this has been used to refine a DTM based
on the NRA profiles. Construction of the DTM followed a two stage process. First the
profiles were “stitched” together to form a surface using a triangular irregular network
approach. Obviously with profiles so far apart any form of interpolation will miss many
major topographical features (rivers, sand banks and so on). The initial surface was
then refined by exploiting the relationship between ground cover and elevation along
the observed profiles. For each cover type the mean and standard deviation of the
elevation was used to generate a range of ‘expected’ values to use as an ‘adaptive
filter’. Each point in the DTM was examined in turn and where the interpolated
surface was much higher or lower than might be expected (given the cover type), the
elevation was adjusted. Where the interpolated elevation was within the expected
bounds it was not altered.
The level of the tide has been calculated using the Admiralty harmonic
method. One secondary port, Wells, is within the study area, but the predicted tidal
range is very low due to the convoluted nature of the channel to the harbour.
Fortunately two other secondary ports, Hunstanton and Cromer are respectively to the
west and east of the region. Tidal heights from these two ports are used to interpolate
values in between.
By combining information about the elevation of each point with the
predictions as to the height of the tide, it is possible to estimate the duration of
submergence at any point.
The distance from the nearest creek has been estimated by reclassifying the image to
try and identify creeks and then apply a buffer around them. Note, however, that even a
resolution of five meters is rather coarse for the complex topography of the typical salt
marsh, this may explain why the mean distance to a creek (80 meters) appears rather
high by this method.
The Effect of Saltmarshes on Sediment Deposition
237
profile information with the CASI imagery the relationship between the shape and
stability of the beach and the vegetation can be revealed.
Fig. 2 shows a profile across Scolt Head Island. Note the dunes and shingle
ridges protecting the salt marsh, and the stability of the profile over a three year period.
Fig. 3 shows a more exposed profile one kilometre to the east of the town of Wells
where a single minor ridge is sufficient to protect stable salt marsh vegetation this is,
however, conspicuously different from that at Scolt Head Island. Fig. 4 shows a profile
mid way between Wells and Blakeney Point where the vegetation is very similar to the
Scolt Head profile, however, the bare sediment is much more dynamic than the in the
other two profiles.
It is interesting to observe the very narrow and consistent range of elevations
within which the different species exist and this has been used to refine a DTM based
on the NRA profiles. Construction of the DTM followed a two stage process. First the
profiles were “stitched” together to form a surface using a triangular irregular network
approach. Obviously with profiles so far apart any form of interpolation will miss many
major topographical features (rivers, sand banks and so on). The initial surface was
then refined by exploiting the relationship between ground cover and elevation along
the observed profiles. For each cover type the mean and standard deviation of the
elevation was used to generate a range of ‘expected’ values to use as an ‘adaptive
filter’. Each point in the DTM was examined in turn and where the interpolated
surface was much higher or lower than might be expected (given the cover type), the
elevation was adjusted. Where the interpolated elevation was within the expected
bounds it was not altered.
The level of the tide has been calculated using the Admiralty harmonic
method. One secondary port, Wells, is within the study area, but the predicted tidal
range is very low due to the convoluted nature of the channel to the harbour.
Fortunately two other secondary ports, Hunstanton and Cromer are respectively to the
west and east of the region. Tidal heights from these two ports are used to interpolate
values in between.
By combining information about the elevation of each point with the
predictions as to the height of the tide, it is possible to estimate the duration of
submergence at any point.