GIS for the Study of Beach Morphodynamics
179
Results
Surface analysis has shown that Dawdon presents a host of different characteristics, in
both size and spatial occurrence of the features that were examined, compared to the
other 2 study areas in Easington and Horden.
The slope maps for Dawdon generally reveal a different morphological profile
in the second half of 1991 and early 1992 from that of later months. A typical example
is shown in Fig. 10(a) for October 1991. Two quite distinct sections can be seen with
the foreshore part being steeper. Aspect maps (example in Fig. 10(b)) show a similar
pattern, with the steeper nearshore part facing east and the backshore part facing west.
In the second half of 1992, this pattern changes completely and the overall trend is that
the mean slope values increase with time (Fig. 2) while the beach surface becomes a
rather undulating surface. This is easily observed in the elevation profiles (Fig. 9).
Slope maps for Easington and Horden do not show the same characteristics as
Dawdon and beach orientation is solely towards the east. No increase in the mean
slope value is observed either (Fig. 2). Changes in beach elevation appear to be
seasonal in most cases. Undulations of mean elevation and mean “cut” values in Fig. 9
highlight the dry-wet season periodicity. In Dawdon, however, certain unusual
patterns (“sink holes” and undulations) in the beach surface prompted us to investigate
the surface development further. Relatively higher values of “cut” changes seem to be
concentrated along a narrow zone at the lower parts of the foreshore in Easington and
Horden, but occur in more distinct patches in Dawdon beach. Notably a sink hole is
apparent at the north end of Dawdon beach during the spring and early summer
months of 1992.
“Cut-fill” changes over the 2s threshold (Fig. 6(a)) indicate that in Dawdon
over the study period, losses of beach material occurred in a much larger area than
those in Easington and Horden. Taking into account the similar topography, geology
and climatological conditions in the 3 study areas, the unusual “cut” patterns in
Dawdon indicate a higher degree of vulnerability at this beach.
To further investigate these observations, the profiles of heights and difference
values were used to test the hypothesis that the height of the beach can be predicted
from a combination of strain values, subsidence and difference features. The plot of cut
features (Fig. 9) shows a good relationship with the edge of underground panels. A
multiple regression of the parameters difference value, strain and subsidence on height
was conducted to test this relationship. In order to be able to use multiple regression
the data must be normally distributed. The normal probability plot of the 26 data
points used showed a good approximation to a straight line so the test was appropriate.
Strain is proportional to subsidence and inversely proportional to depth so that the
maximum strain over an extraction is proportional to S/h, where S is the maximum
subsidence and h is the depth of the seam. It is appropriate to just calculate the
subsidence and strain profiles for the seam nearest the surface as strain decreases with
the depth of the seam. Multiple extraction will have an impact however but is not
considered here.
179
Results
Surface analysis has shown that Dawdon presents a host of different characteristics, in
both size and spatial occurrence of the features that were examined, compared to the
other 2 study areas in Easington and Horden.
The slope maps for Dawdon generally reveal a different morphological profile
in the second half of 1991 and early 1992 from that of later months. A typical example
is shown in Fig. 10(a) for October 1991. Two quite distinct sections can be seen with
the foreshore part being steeper. Aspect maps (example in Fig. 10(b)) show a similar
pattern, with the steeper nearshore part facing east and the backshore part facing west.
In the second half of 1992, this pattern changes completely and the overall trend is that
the mean slope values increase with time (Fig. 2) while the beach surface becomes a
rather undulating surface. This is easily observed in the elevation profiles (Fig. 9).
Slope maps for Easington and Horden do not show the same characteristics as
Dawdon and beach orientation is solely towards the east. No increase in the mean
slope value is observed either (Fig. 2). Changes in beach elevation appear to be
seasonal in most cases. Undulations of mean elevation and mean “cut” values in Fig. 9
highlight the dry-wet season periodicity. In Dawdon, however, certain unusual
patterns (“sink holes” and undulations) in the beach surface prompted us to investigate
the surface development further. Relatively higher values of “cut” changes seem to be
concentrated along a narrow zone at the lower parts of the foreshore in Easington and
Horden, but occur in more distinct patches in Dawdon beach. Notably a sink hole is
apparent at the north end of Dawdon beach during the spring and early summer
months of 1992.
“Cut-fill” changes over the 2s threshold (Fig. 6(a)) indicate that in Dawdon
over the study period, losses of beach material occurred in a much larger area than
those in Easington and Horden. Taking into account the similar topography, geology
and climatological conditions in the 3 study areas, the unusual “cut” patterns in
Dawdon indicate a higher degree of vulnerability at this beach.
To further investigate these observations, the profiles of heights and difference
values were used to test the hypothesis that the height of the beach can be predicted
from a combination of strain values, subsidence and difference features. The plot of cut
features (Fig. 9) shows a good relationship with the edge of underground panels. A
multiple regression of the parameters difference value, strain and subsidence on height
was conducted to test this relationship. In order to be able to use multiple regression
the data must be normally distributed. The normal probability plot of the 26 data
points used showed a good approximation to a straight line so the test was appropriate.
Strain is proportional to subsidence and inversely proportional to depth so that the
maximum strain over an extraction is proportional to S/h, where S is the maximum
subsidence and h is the depth of the seam. It is appropriate to just calculate the
subsidence and strain profiles for the seam nearest the surface as strain decreases with
the depth of the seam. Multiple extraction will have an impact however but is not
considered here.