GIS for the Study of Beach Morphodynamics
177
“cut” changes calculated this way can be seen in Fig. 5. Unusual negative (cut) and
positive (fill) changes, produced by assuming a mean - 2s / mean + 2s threshold, were
reclassified using a binary classification. Cumulative maps for unusual “cut” and “fill”
changes where then produced by adding the reclassified “cut” and “fill” maps. The
resulting maps (2 for each study area) show occurrence of unusual negative and
positive changes (Fig. 6a, b, and c).
b. Subsidence
Data was obtained from British Coal from underground abandonment coal plans at a
scale of 1:10,560 covering the beaches in the study. From these plans, information on
the seams worked (John Ellis pers. comm.), and the charts supplied by the Subsidence
Engineer’s Handbook (Anon, 1975) it was possible to calculate a prediction of
maximum subsidence that would affect the beaches. Table 2 shows the 6 main seams
in the study areas.
The calculated value gives a theoretical maximum. It is more practical to
calculate how this subsidence changes from this maximum over the centre of a worked
panel to the limits of subsidence impact at the surface. This value is a function of the
177
“cut” changes calculated this way can be seen in Fig. 5. Unusual negative (cut) and
positive (fill) changes, produced by assuming a mean - 2s / mean + 2s threshold, were
reclassified using a binary classification. Cumulative maps for unusual “cut” and “fill”
changes where then produced by adding the reclassified “cut” and “fill” maps. The
resulting maps (2 for each study area) show occurrence of unusual negative and
positive changes (Fig. 6a, b, and c).
b. Subsidence
Data was obtained from British Coal from underground abandonment coal plans at a
scale of 1:10,560 covering the beaches in the study. From these plans, information on
the seams worked (John Ellis pers. comm.), and the charts supplied by the Subsidence
Engineer’s Handbook (Anon, 1975) it was possible to calculate a prediction of
maximum subsidence that would affect the beaches. Table 2 shows the 6 main seams
in the study areas.
The calculated value gives a theoretical maximum. It is more practical to
calculate how this subsidence changes from this maximum over the centre of a worked
panel to the limits of subsidence impact at the surface. This value is a function of the