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Mapping flood related hazards in karst using KARSYS approach. Application to the Beuchire-Creugenat karst system (Ju, Switzerland)

Type of publication Peer-reviewed
Publikationsform Proceedings (peer-reviewed)
Author Vouillamoz Jonathan, Malard Arnauld, Schwab-Rouge Gabrielle, Weber Eric, Jeannin Pierre-Yves,
Project SWISSKARST: Towards a sustainable management of karst waters in Switzerland
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Proceedings (peer-reviewed)

Title of proceedings 13th Multidisciplinary Conference on Sinkholes and the Engineering and Environmental impact of karst
Place Carlsbad, New Mexico

Open Access

Abstract

The city of Porrentruy (JU, Switzerland) is vulnerable to flooding from karst water draining the system of the Beuchire-Creugenat. Major flood events in 1804 and 1901 led to heavy damages throughout the city and its vicinity. Furthermore small-scale flood events have been recorded five times in the last 30 years - each resulting in substantial costs. The Beuchire-Creugenat karst system is characterized by a perennial outlet (the Beuchire spring) and several overflow outlets (among which the Creugenat temporary outflow is the most significant one) where the discharge rate often exceeds 15 m3/s. The ratio between rainfall intensity and discharge rate of the overflow springs is not closely correlated. Therefore, the discharge rates and the conditions at which a certain overflow becomes active could not be assessed without a comprehensive understanding of the karst system behavior. Thus, the establishment of effective flood risk management measures remains significant challenge. In order to assess similar flood events and to determine the most flooding vulnerable areas, the KARSYS approach has been applied to the Beuchire-Creugenat karst system. A detailed geological 3D model of the study area has been built in order to reproduce the aquifer base geometry, the extension of its expected saturated part(s) and the position of the main vadose flowpaths “drainage axes”. This approach enabled the catchment area delineation by combination of subterraneous drainage axes. The comparison of the discharge time series of the main springs and the relevant rainfalls (~10-year series) provides sufficient implications for understanding and consequent reproducing of threshold functionality of 2the karst system exposed to flooding due to rainfall events. A relationship could be established between rainfall intensity/frequency (return period) and the corresponding elevation of the groundwater level within the karst conduits (or respectively, the relevant spring discharge rates). The known overflow springs have been added in the 3D model. The areas where (and when) karst groundwater is expected to reach the ground surface during extreme high-water events could be identified as potential overflow springs. Such draining sensitive areas have been delineated and mapped according to the calculated return period of multiannual, 30- and 300- years flood events and the relevant maximum discharge rates at the main outlets have been assessed.
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