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| Titel |
A laser profilometry technique for monitoring fluvial dike breaching in
laboratory experiments |
| VerfasserIn |
Benjamin Dewals, Ismail Rifai, Sébastien Erpicum, Pierre Archambeau, Damien Violeau, Michel Pirotton, Kamal El Kadi Abderrezzak |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250140333
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| Publikation (Nr.) |
 EGU/EGU2017-3707.pdf |
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| Zusammenfassung |
| A challenging aspect for experimental modelling of fluvial dike breaching is the continuous
monitoring of the transient breach geometry. In dam breaching cases induced by flow
overtopping over the whole breach crest (plane erosion), a side view through a glass wall is
sufficient to monitor the breach formation. This approach can be extended for 3D dam breach
tests (spatial erosion) if the glass wall is located along the breach centreline. In contrast, using
a side view does not apply for monitoring fluvial dike breaching, because the breach is not
symmetric in this case. We present a non-intrusive, high resolution technique to record the
breach development in experimental models of fluvial dikes by means of a laser profilometry
(Rifai et al. 2016).
Most methods used for monitoring dam and dike breaching involve the projection of a
pattern (fringes, grid) on the dam or dike body and the analysis of its deformation on images
recorded during the breaching (e.g., Pickert et al. 2011, Frank and Hager 2014).
A major limitation of these methods stems from reflection on the water surface,
particularly in the vicinity of the breach where the free surface is irregular and
rippled. This issue was addressed by Spinewine et al. (2004), who used a single
laser sheet so that reflections on the water surface were strongly limited and did
not hamper the accurate processing of each image. We have developed a similar
laser profilometry technique tailored for laboratory experiments on fluvial dike
breaching.
The setup is simple and relatively low cost. It consists of a digital video camera
(resolution of 1920 × 1080 pixels at 60 frames per second) and a swiping red
diode 30 mW laser that enables the projection of a laser sheet over the dike body.
The 2D image coordinates of each deformed laser profile incident on the dike are
transformed into 3D object coordinates using the Direct Linear Transformation (DLT)
algorithm. All 3D object coordinates computed over a swiping cycle of the laser are
merged to generate a cloud of points. The DLT-based image processing method
uses control points and reference axes, so that no prior knowledge is needed on the
position, orientation and intrinsic characteristics of the camera, nor on the laser
position.
Refraction of the light and laser rays across the water surface needs to be taken into
account, because the dike is partially submerged during the experiments. An ad hoc
correction is therefore applied using the Snell-Descartes law. For this purpose,
planar approximations are used to describe the shape of the water surface. In the
presentation, we will discuss the resulting uncertainty and will detail the validation of
the developed method based on configurations of known geometry with various
complexity.
The presented laser profilometry technique allows for a rapid non-intrusive measurement
of the dike geometry evolution. It is readily available for laboratory experiments and has
proven its performance (Rifai et al. 2017). Further adjustments are needed for its application
to cohesive dike material due to the reduced visibility resulting from the higher turbidity of
water.
References
Frank, P.-J., Hager, W.H. (2014). Spatial dike breach: Accuracy of photogrammetric
measurement system. Proc. of the International Conference on Fluvial Hydraulics, River
Flow 2014, 1647-1654.
Pickert, G., Weitbrecht, V., Bieberstein A. (2011). Beaching of overtopped river
embankments controlled by apparent cohesion. Journal of Hydraulic Research 49:143–156.
Rifai, I., Erpicum, S., Archambeau, P., Violeau, D., Pirotton, M., El kadi Abderrezzak, K.,
Dewals, B. (2016). Monitoring topography of laboratory fluvial dike models subjected to
breaching based on a laser profilometry technique. Proc. of the International Symposium on
River Sedimentation (ISRS): Stuttgart, 19-22 September 2016.
Rifai, I., Erpicum, S., Archambeau, P., Violeau, D., Pirotton, M., El kadi Abderrezzak, K.,
Dewals, B. (2017). Overtopping induced failure of non-cohesive, homogenous fluvial dikes.
Water Resources Research, under revision.
Spinewine, B., Delobbe, A., Elslander, L., Zech, Y. (2004). Experimental investigation of
the breach growth process in sand dikes. Proc. of the International Conference on Fluvial
Hydraulics, River Flow 2004, 2:983–991. |
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