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| Titel |
Coastal cliff retreat rates: a probabilistic approach fed by Terrestrial Laser Scanner monitoring data |
| VerfasserIn |
Thomas Dewez, Céline Cnudde |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250048063
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| Zusammenfassung |
| Cliff retreat is a major concern for coastal communities and coastal risk management.
The stochastic nature of cliff collapse prevents predicting and forecasting these
events. Repeated terrestrial laser surveys of a cliff face enable the compilation of
an inventory of all rockfall events occurring in a given period and afford a fine
geometric description of them. Using this inventory, it is possible to examine the
frequency distribution of different geometric properties. In this study, we focus on
assessing the recurrence of individual cliff retreat events in an attempt to establish a
probabilistic relationship between amount of cliff retreat and return period. The analysis is
based on a catalogue of more than 8500 events that occurred between December
2005 and April 2008 on the 750-m-long Mesnil Val coastal chalk cliff, Normandy.
Individual rockfall thickness are comprised between 0.03 m and 19 m. The cumulated
complementory distribution function (CCDF) of rockfall thickness describes erosion hazard
and was computed for all events. The CCDF fits a power law but with different
scaling exponents according to retreat range. Power laws for rockfalls thinner than
10 cm or thicker than 1 m scale with an exponent close to 2, while that of events
between 10 cm and 1 m thick scale with an exponent close to 1. We suggest that
rockfalls of the intermediate range (0.1 – 1m) are constrained by the geological
structure of the massif (bedding and joints/faults). Thinner or thicker events do
not see these structures and behave in a different way. The practical application
is this relationship is to determine the return period of hazardous rockfalls. For
instance, rockfalls with a thickness of 10 m may occur at Mesnil Val every 14 months
which is an information readily usable by urban planners and the civil security. |
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