Influence of non-linear effects upon surge elevations along the west coast of Britain |
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Authors: | John Eric Jones Alan Marshall Davies |
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Institution: | (1) Proudman Oceanographic Laboratory, 6 Brownlow Street, Liverpool, Merseyside, L3 5DA, UK |
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Abstract: | A two-dimensional vertically integrated hydrodynamic finite-element model of the west coast of Britain is used to examine
the response of the region to extreme meteorological forcing. The extent to which tide–surge interaction modifies the computed
surge elevation and current distributions is examined in detail. The nature of the finite-element model with its ability to
refine the mesh in nearshore regions is ideal for examining the influence of non-linear effects upon surges in these regions.
Calculations using spatially uniform orthogonal wind stresses show that the surge elevation and current in shallow water are
particularly sensitive to the method used to remove the tide as a result of the highly non-linear nature of the tide–surge
interaction in these regions. The most accurate means of de-tiding the solution is by subtracting a tide derived by harmonic
analysis of the tide and surge time series at the time of the surge. Subtracting a tide-only solution (the usual approach)
leads to tidal energy leaking into the surge solution. Calculations show that this arises because the surge modifies the tidal
amplitude and phase in shallow-water regions to such an extent that they are appreciably different to those found in the tide-only
calculation. Results suggest that this problem becomes more important, as nearshore meshes are refined in an attempt to improve
surge prediction. This suggests that in the future, highly accurate fine-mesh models will be required to compute total water
levels without the present linear separation into tidal and surge signal used in operational surge prediction. |
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Keywords: | De-tiding Finite-element model Tide– surge interaction |
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