140
R.H. Charlier and Chr. P. De Meyer
in which :
y = distance from the intersection of the erosion profile and storm surge level
in m.
h = depth below storm surge level in m.
The erosion profile develops in such a way that the erosion equals the
sedimentation. After the storm surge the slope of the dune front is assumed to be
1:1, while the erosion profile has developed to a depth
db= 1.25 H~b
(90)
where :
db
=
H~b =
breaker depth
significant wave height at the breaker depth during maximum storm
surge level.
At the depth db the erosion profile ends vertically. This already demonstrates that
the aim was not tried to obtain a physically correct description of the dune
erosion, but only to activate a simple computational method.
In order to arrive at a more reliable computational method a large number of
experiments with different scales and different types of sand were carried out.
Further irregular waves were applied to avoid the effect of secondary waves. A
detailed analysis of the measurements resulted into a set of scale relationships
for convening the model results to prototype values, viz.
) 0.28
n 1 / n d = n d / n2w
(91)
0.5
n t = n d
(92)
in which :
nl
= length scale
nd = depth scale
nw = scale of fall velocity of sand
nt
= morphologic time scale
The above mentioned scale relations were verified by large scale tests in the
Delta-flume (The Netherlands). For standard conditions with Hos = 7.6 m, Tp =
12 s and w = 0.0268 m/s the erosion profile is defined as follows :
h =
0.4714 (y + 18) °s - 2.00
(93)