Geoscience Reference
In-Depth Information
Intrusive measurements are not applicable as they disturb the erosion process. Other
methods were used to determine spatial breach profiles. Coleman et al. (
2002
)
drained the reservoir at several stages of the erosion process and recorded the dried
three-dimensional surface topography using a surface profile measurement system.
They describe the breach profiles in detail and present a breach-discharge equation.
However, the effort to determine these erosion profiles is comparatively high.
Pickert et al. (
2004
) used a Fringe Projection to continuously measure 3D breach
profiles. An alternating black/transparent stripe pattern was produced on the dike
surface using a slide projector and recorded with a video camera through the
channel sidewall. The breach process could only be observed in the initial phase,
however, as the observation through the sidewall failed for large breach widths.
Rozov (
2003
) measured the breach process using washout indicators installed
inside the model dam. The indicators work on the principle of breaking a circuit
if it is reached by the moving sediment. A detailed analysis of the breach profiles
was not provided.
A fast and reliable method to determine the 3D breach profile during a dike
breach under laboratory conditions is still missing. To fill in this gap, an effort was
made to apply a new non-intrusive videometric system, developed by AICON
®
3D
Systems Ltd
1
(Braunschweig, Germany). Preliminary experiences on the features
of this system are presented below.
2 Test Setup
2.1 Hydraulic Model
The experiments were conducted in a glass-sided model channel at VAW (Fig.
1a
).
Its discharge capacity is
Q
130 L/s, it is 1.0-m wide and 9-m long, with a
working section of roughly 5 m, and its bottom is horizontal. The channel is suited
for the 3D tests described below. Test dikes of up to 0.50-m height can be erected,
the tailwater is remote-controlled with a flap gate at the channel end and the flow
features can be optically recorded either through the large channel windows or from
the top. A horizontally graded, washed river gravel of median diameter
d
50
¼
¼
1.14 mm
was used as sediment bed. The dike consisted of the same material and was erected
above the sediment bed (Fig.
1b
). For preliminary tests, the dimensions of the dike
were: dike height
w
¼
0.20 m, dike width
b
¼
1.0 m, dike crest length
L
K
¼
0.10 m
with both the up- and downstream dike slopes
S
o
¼
1:3 (V:H).
A triangular pilot channel was cut in the embankment crest along the channel
sidewall, to initiate the breach process, with the channel wall simulating the breach
centerline. This allowed recording the longitudinal breach profiles along the breach
centerline and the corresponding flow depths. The reservoir filling was comparatively
1
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