Poljes, Ponors and Their Catchments


O. Bonacci


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Treatsie on Geomorphology

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Poljes can be defined as depressions in limestone karst. They commonly occur as large-scale landforms in tectonically active karst areas. Their origin is generally polygenetic. A distinctive subtype of polje, the ‘turlough’, occurs in many formerly glaciated or glacial-margin terrains. Poljes exhibit complex hydrological and hydrogeological features and characteristics, such as permanent and temporary springs and rivers, losing and sinking rivers, and swallow holes and estavelles. From the hydrologic–hydrogeologic perspective, a polje is to be considered as part of a wider system. It cannot be treated as an independent system, but only as a subsystem in the process of surface and groundwater flow through the karst massif. Poljes are regularly flooded in the cold and wet periods of the year. Ponors or swallow holes represent fissures in the karst massif through which the water sinks underground. The determination of the catchment area for a karst polje is an unreliable procedure due to unknown morphology of underground karst features. Anthropogenic influences on the hydrological–hydrogeological regime of the poljes can be considered under the following four categories: (1) water storage; (2) increase in the capacity of outlet structures; (3) surface hydrotechnical aspects; and (4) other works.

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