51 
Fig. 7.2.6: Water level evolution near Shetland (input signal: 3 positive single signals, 
T 1800 s, wave height 3 m, from the north N, from the south S and from the west W, 
North-East Atlantic model 10 km) 
7.3 North Sea signal from the west 
As has been explained in section 7.1, the simulations run on the North Sea model (grid 
spacing 2 km) were not carried out using boundary values from the North-East Atlantic model 
as input signal but an analytical standard wave train (3 positive single waves, period 1800 s, 
wave height 5 m). First, a boundary signal from the west was prescribed. The signal is 
identical in the western part of the Channel and off Scotland, where it starts at the same time 
(f=0). This specific kind of boundary condition is not to be expected from the results of 
section 7.2. The initial phase of the simulation should rather be considered the simultaneous 
representation of two theoretical types of boundary conditions. 
7.3.1 Propagation 
The input signal initially leads to very high local water levels, both in the north and in the 
Channel (Fig. 7.3.1). In Plymouth, for example, about 8 m is reached. In the north, 
propagation of the single waves is circular (Fig. 7.3.2), with subsequent superposition with a 
diffraction pattern caused by the Norwegian coast (Fig. 7.3.3). In general, this signal is 
weaker in the North Sea than a comparable signal entering from the north (cf. section 7.4). 
This is mainly because there is less energy available right from the start (incoming signals 
travel across a shorter section of the boundary). The wave front then widens due to circular 
propagation, whereas in subsequent simulations (sections 7.4 and 7.5) the wave front initially 
maintains a relatively constant length. 
Signal propagation in the Channel is slow, but the high resolution allows the propagation to 
be modelled along the continental coastline into the North Sea (Figs. 7.3.3 and 7.3.4). 
Finally, the signals from the Channel and from the north superimpose (Figs. 7.3.5 and 7.3.2).