39 
In contrast, in routine operational use of the North Sea models, it is primarily a water level 
signal (tide, external surge) that is to be transported across the open boundary into the North 
Sea region. Therefore, ij ext in this case is prescribed. For the simulations shown in sections 
7.3 and 7.4, u ext at the North Sea boundary was prescribed as in the North-East Atlantic 
model, and i] ext was determined by t] + ext = 0 at the northern boundary and by ij ex ~ = 0 at the 
western boundary. In the computations in section 7.5, however, the originally used 
formulation of the boundary condition was retained and, like tidal waves and external surges, 
the external signal at the North Sea boundary was prescribed by ij ext . 
6.1.7 Propagation and modification in near-shore areas and estuaries 
The propagation of tsunami in near-shore areas was studied in various model simulations 
(10.5: BEN04). Pedersen (2004) considers dispersion important in this test case, and the 
inclusion of non-linearity less important. The decisive aspect in numerical simulations is the 
grid resolution. Chubarov et al. (2003) reproduced water level rise in the wave shadow of an 
island and obtained good results with a hydrostatic model, though with a grid spacing of 50 
m. Besides, comparative computations (Pedersen 2004) showed that hydrostatic models 
adequately simulate water levels but underestimate the velocity of water particles. 
The tsunami of December 2004 has led to an intensification of research in the modelling of 
nearshore processes in the Indian Ocean, also in Germany. The Center for Marine and 
Atmospheric Sciences (ZMAW, Zentrum für Marine und Atmosphärische Wissenschaften), 
the Institute for Coastal Research at GKSS-Research Center (GKSS, GKSS- 
Forschungszentrum) and other German institutions have taken up the subject (e.g. Androsov 
et al. 2005). As part of a BMBF project, GKSS uses the MIKE21 BW model based on 
Boussinesq equations (10.4: MIK21, Günther et al. 2005). Simulations of German coastal 
areas might benefit from these studies. Processes on the German coasts are expected to be 
similar but, referring to section 5.4.2, are likely to involve less energy than the Sumatra 
event. 
Bore modelling requires Lagrangian models or parametric representation. Tsunami travelling 
into estuaries become shorter, higher, and steeper in their leading part under the influence of 
bottom friction and funnelling, comparable to tidal waves. They may finally form a bore. Fig. 
6.1.1 shows the evolution of water levels from Cuxhaven to Geesthacht during the 
propagation of a shelf-modified input signal of an original height of 3 m, simulated by the 
MARTIN model of BAW (Millbradt 2002). The BSFI model system is not capable of modelling 
tsunami wave propagation into river estuaries.