D28: Internal seiche mixing study - Hydromod

Integrated Water Resource Management for Important Deep European Lakes and their Catchment Areas
EUROLAKES
D28: Internal seiche mixing study
FP5_Contract No.: EVK1-CT1999-00004
Version: 1.2
Date: 24.08.2004
File: D28.doc
Page 77 of 92
variations of the pair of upper and lower layer depths on one hand and the density difference,
ε, on the other hand. This peculiar variety of two-layer cases covered by one
set of eigenfunctions means a useful advantage, as the same calculations can be exploited
for certain different two-layer approaches.
The current fields of the first and ninth modes are depicted in Figure 50 and Figure 51
for the case in spring and in Figure 53 and Figure 54 for that in late summer. Additionally,
the currents of the eleventh mode are enclosed in Figure 52 and Figure 55 in order
to emphasize the practical use by a peculiar application, which Hollan (1995) carried
out and is outlined below. Except for the reference to the amplitude normalisation the
relative variation of the structures in the current fields can be detected well from the
diagrams. They consist each of a pair, showing the current ellipses in the upper diagram
which indicate the position of the head of the current vector when turning during
one cycle of oscillation. The main axis of the ellipses shows the orientation of the predominant
current during a wave cycle, while the small axis gives the maximum transverse
currents a quarter of the period later than the main currents. In the lower diagram
the information is compiled, which concerns the sense of rotation at a given moment.
Included into this stick representation is the sense of rotation of the current vector. The
illustration of the phase relation and the sense of rotation throughout the lake is secondary
for a rough evaluation, as this information is more important for inspection of
closely adjacent conditions. The assessment of the local intensity of the currents is very
comprehensive in the upper diagram. There is remarkable variation of the intensity and
relative difference between the main and the transverse currents. This is easily perceived
in the different examples and left to the reader for comparison.