28 
'7.5 
Fig. 5.4.2: Amplitude development on a 1:2,500 shelf slope at a shelf width of 100 km (left 
scale: depth, “German Bight”) 
Fig. 5.4.3: Amplitude development on a 1:4,000 shelf slope at a shelf width of 800 km (left 
scale: depth, “North Sea”)Topographic effects 
5.4.3 Topographic effects 
In the barotropic two-dimensional North Sea models referred to in sections 7.3 to 7.5, the 
dissipation of energy through internal friction and bottom friction is taken into account in 
complex form (Dick et al. 2001). Fig. 7.4.9 shows no asymptotic behaviour of wave height, 
but a limitation. A successive increase in initial wave heights by 1 m leads to an increase of 
just 0.05 m in wave height for waves arriving near the coast (at Cuxhaven, first signal in Fig. 
7.4.9). Flowever, Cuxhaven is not a well-chosen example because at this location even the 
primary signal is caused exclusively by diffraction (compare section 7.4.2). Fig. 5.4.4 shows 
peak water levels at selected stations along the North Sea coast. The lines between Wick 
and Borkum are comparable to those in Fig. 5.4.3. The high values at North Shields and the 
additional values from Ijmuiden til Hirtshals indicate an influence other than dissipation. 
Bottom topography and the shape of the coastline influence the propagation and modification 
of tsunami-size waves in various ways. Fig. 7.3.1 shows a circular wave in the northwest that 
has been caused by diffraction. Figs. 7.4.1 to 7.4.6 are examples of the superposition of such 
secondary waves (interference), which may lead to very high water levels, especially in bays 
where wave reflection is a contributing factor. 
Waves on the shelf are reflected and scattered by topographic features, just like they are in 
the deep ocean and on the continental slope. Especially pronounced in the North Sea is the 
influence of topography on the propagation velocity <Jgh and on changes in the direction of 
propagation due to refraction (cf. figures in sections 7.3 - 7.5). 
Such wave phenomena are understood (e.g. Masselink 2005) and have been discussed with 
respect to tsunami (Camfield 1990, Mofjeld 2000). To simulate these processes in detail, a 
good representation of the bottom topography is indispensable.