4.1.2. Resistant layer thickness and position
It has been demonstrated above how a more resistant layer influences
shore platform geomorphology but not necessarily the rates of
cliff toe retreat when situated below MSL. To investigate the effect of
thickness of the resistant layer, a series of analyses were run in which
the thickness of a band of 5× relatively more resistant material was
increased in steps of 1 m from a constant base elevation of 6 m below
MSL (Table 2).
The results showed that when the resistant layer thickness exceeds
5m(upper limit at 1m below MSL), a marked change in the cliff toe position
and a reduction in retreat rates occur. However, above a resistant
layer thickness of 9 m (upper limit at 3 m above MSL), the effect of further increases in layer thickness is not apparent in the non dimensional
rate of retreat by the end of the model simulation, as
outlined in Fig. 6. This would be expected given the vertical extent of
marine processes modelled in SCAPE. Above this limit changes in material
strength will only affect geotechnical processes in the cliff face
which, as noted in Section 2, are not considered in SCAPE 2D. However,
in terms of marine processes the results suggest that the position of the
layer relative toMSL may bemore important than its thickness in determining
its influence on recession rate.
4.1.2. Resistant layer thickness and positionIt has been demonstrated above how a more resistant layer influencesshore platform geomorphology but not necessarily the rates ofcliff toe retreat when situated below MSL. To investigate the effect ofthickness of the resistant layer, a series of analyses were run in whichthe thickness of a band of 5× relatively more resistant material wasincreased in steps of 1 m from a constant base elevation of 6 m belowMSL (Table 2).The results showed that when the resistant layer thickness exceeds5m(upper limit at 1m below MSL), a marked change in the cliff toe positionand a reduction in retreat rates occur. However, above a resistantlayer thickness of 9 m (upper limit at 3 m above MSL), the effect of further increases in layer thickness is not apparent in the non dimensionalrate of retreat by the end of the model simulation, asoutlined in Fig. 6. This would be expected given the vertical extent ofmarine processes modelled in SCAPE. Above this limit changes in materialstrength will only affect geotechnical processes in the cliff facewhich, as noted in Section 2, are not considered in SCAPE 2D. However,in terms of marine processes the results suggest that the position of thelayer relative toMSL may bemore important than its thickness in determiningits influence on recession rate.
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