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| Titel |
Fluvial dike breaching due to overtopping: how different is it from dam breaching? |
| VerfasserIn |
Ismail Rifai, Sébastien Erpicum, Pierre Archambeau, Damien Violeau, Michel Pirotton, Kamal El Kadi Abderrezzak, Benjamin Dewals |
| 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 |
250140325
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| Publikation (Nr.) |
 EGU/EGU2017-3698.pdf |
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| Zusammenfassung |
| During floods in large rivers, casualties and extent of damage are often aggravated by breach
formation across fluvial dikes. The most frequent cause of breaching is flow overtopping.
Predicting the breach geometry and associated outflow hydrograph is of critical importance
for estimating the inundation characteristics in the floodplain and the resulting flood
risk.
Because fluvial dikes are built along a main channel that conveys flowing water, fluvial
dike breaching differs from dam breaching, in which the embankment is built across the
channel downstream of a reservoir. While a vast body of studies exists on dam breaching
configuration (e.g., Schmocker et al. 2012, 2014, Müller et al. 2016), little is known on
specific aspects of fluvial dike breaching.
We performed laboratory experiments that highlight the specific erosion processes
governing fluvial dike breaching (Rifai et al. 2017a). The experimental setup includes a 10 m
long and 1 m wide main channel, separated from a floodplain by a 0.3 m high dike of
trapezoidal cross-section. The dike material was homogeneous and made of uniform sand. A
rectangular initial notch was cut in the crest to initiate 3D breaching. The breach development
was monitored continuously using a self-developed laser profilometry technique (Rifai et al.
2016).
The observations reveal that the breach develops in two stages. First, a combined
breach deepening and widening occur, together with a gradual shift of the breach
centreline toward the downstream side of the main channel. Later, the breach widening
continues only toward the downstream side of the main channel, highlighting a
significant influence of flow momentum in the main channel. Moreover, the breach
cross-section is tilted toward the downstream end of the main channel, which is a
signature of an asymmetric velocity distribution through the breach (Rifai et al.
2017b).
When the inflow discharge in the main channel is increased, the breach development
becomes much faster (e.g., seven times faster for a 150 % increase in the inflow discharge).
When an equilibrium state is reached at the end of the test, the breach centreline orientation is
found consistent with the theory of flow over a lateral weir.
In the experiments, the boundary condition at the downstream end of the main channel is
a lumped representation of river characteristics downstream of the breach section.
In real-world conditions, these river characteristics influence the flow partition
between the breach and the main channel. Therefore, we tested several downstream
boundary conditions (perforated plane, rectilinear weir and sluice gate). For the
same inflow discharge and water levels, they lead to significantly different breach
geometries.
The findings of this research shed light on key mechanisms occurring in fluvial dike
breaching, which differ substantially from those in dam breaching. These specific features
need to be incorporated in flood risk analyses involving fluvial dike breaching.
This research also delivers a unique experimental database of high resolution continuous
monitoring of the breach geometry under various flow conditions. The datasets are freely
available for engineers and researchers willing to assess the performance of numerical models
to simulate dike breaching and resulting flood.
References
Müller, C., Frank, P.-J., Hager, W.H. (2016). Dyke overtopping: effects of shape and
headwater elevation. Journal of Hydraulic Research, 54(4), 410-422.
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. International Symposium on River
Sedimentation (ISRS), 19-22 September 2016, Stuttgart.
Rifai, I., Erpicum, S., Archambeau, P., Violeau, D., Pirotton, M., El kadi Abderrezzak, K.,
Dewals, B. (2017a). Overtopping induced failure of non-cohesive, homogenous fluvial dikes.
Water Resources Research, under revision.
Rifai, I., Erpicum, S., Archambeau, P., Violeau, D., Pirotton, M., El kadi Abderrezzak, K.,
Dewals, B. (2017b). Discussion of: Laboratory Study on 3D Flow Structures Induced by
Zero-Height Side Weir and Implications for 1D Modeling. Journal of Hydraulic Engineering,
07016010.
doi: 10.1061/(ASCE)HY.1943-7900.0001256
Schmocker, L., Frank, P.-J., Hager, W.H. (2014). Overtopping dike-breach: Effect of grain
size distribution. Journal of Hydraulic Research, 52(4), 559-564.
Schmocker, L., Hager, W.H. (2012). Plane dike-breach due to overtopping: Effects of
sediment, dike height and discharge. Journal of Hydraulic Research, 50(6), 576-586. |
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