30 
BOKIv FORMATION 
BOKIv FORMATION 
Fig. 5.5.1: Change in signal shape near the coast (linear Boussinesq equations, ij surface 
elevation, h undisturbed water depth, 10.5: PEDpT). 
Non-linear effects would finally cause the wave to break and form a bore. Since the breaking 
of a tsunami involves considerable dissipation of energy, shoaling does not lead to a further 
increase in the wave height of the bore despite decreasing water depth, but wave height 
even decreases again (Fig. 5.5.2, right). Bore formation has been parameterised in the 
course of the exemplary simulation of (10.5:PEDpT). 
BORE FORMATION BORE FORMATION 
Fig. 5.5.2: Bore formation (linear Boussinesq equations, ij surface elevation, h undisturbed 
water depth, 10.5: PEDpT). 
A tsunami turning into a bore does so along the entire shore. Tidal waves in estuaries form 
bores mainly under the influence of a change in cross section. In some funnel-shaped river 
estuaries narrowing toward upstream, the height increase of the tidal wave is so sudden that 
it takes the shape of a surf wave (Dietrich et al. 1975, Figs. 8.45 and 10.6: CAR04). Also 
tsunami travelling into estuaries may develop into this type of bore. 
The numerical simulation of processes close to the coastline and the propagation of tsunami 
on land are still subject to intensive research (Geist et al. 2006).