Understanding flooding in poljes: A modelling perspective


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Journal of Hydrology

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Poljes are large flat closed depressions that can be found in most karst areas around the world. They are prone to regular flooding, which occurs after abundant rainfall or snowmelt events. The floods can form several meters deep intermittent lakes that can persist for months. Human settlements around poljes have been traditionally positioned above the level of the most severe floods. However, many neighbouring villages expanded during the last decades to areas that might be endangered by large flood events. In addition, a recent study has shown that several poljes encountered floods of more severe amplitude in mid-Holocene due to a prevailing humid climate. As current knowledge of polje’s hydrology appears to be still insufficient, further research is needed. This work aims to identify the factors controlling polje flooding and evaluates their impact on the flood amplitude and duration. To do so, a list of parameters potentially controlling flooding is established. The relevance of each parameter is tested by using two idealized numerical models. The first one considers exclusively the polje from the springs to the ponors, whereas the second integrates the aquifer adjacent to the polje outflow side. First results show the usefulness of simple numerical models to identify the effect of each parameter on the flood amplitude and duration. The findings are combined to simulate a flood of medium intensity and long duration that occurred on a typical polje. A comparison of the results with real data demonstrates that the aquifer draining the polje needs to be considered to understand properly the flooding dynamics. The approach presented within this work has the potential to be used in other poljes encountering similar hydrological situations, but also lays foundation for flooding modelling in other karst areas.

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