Polje

Polje (. . Kroat / serb / bosn / slow: .. Field, plural: Polya ) is an out of the Dinaric Karst acquired geomorphological term for a Karstverebnung that tied to specific geological- tectonic conditions predominantly occurs in subtropical and tropical karst mountains.

Poljes up several hundred square kilometers (eg Popovo polje polje Livansko, Gacko polje ) of a few square kilometers occupy space. Make significant hydrological nodes in karst hydrological system. Therefore, in poljes always occur sink-holes, in the larger also Sickerflüsse on.

( Hydro) geology

The karst polje is, however, not found in all karst areas, but depends on the structure of the geological structures whose age and distortions from and what stage of development as a result, are the poljebildenden karstification on site. In size and appearance impressive examples can be found in the countries of the Dinaric Alps (Slovenia, Croatia, Bosnia - Herzegovina, Montenegro), in the Apennines of Italy, in Cantabria and Andalusia in Spain and on the Peloponnese.

Geomorphological is a Polje a trough-shaped valley or hollow shape - is surrounded by precipitous mountain formations - usually on all sides. The formation may emerge when ( at least) the younger rock strata are carbonate rocks (limestone, dolomite) or gypsum. The bottom of such a basin consists of sedimentary deposits, which are thicker and may have several hundred meters in thickness. The sediments may at its surface is very stony, dry deposits or loamy / clayey soils be - the one barren, the other very fertile (both even next to each other near Grahovo ). The sedimentary layers are water thawing to waterproof depending on the composition. The sole and the bounding edges of the Polje, however, are carbonate rocks that have been chemically broken down by the water of rainfall and pelvis in geological times faster than physically or penetrated (see weathering ). In these ever- growing form openings: cracks, fissures, sinkholes ( sink holes ) and whole cave systems, can completely leave the water in the basin -collecting. Thus, the relief energy remains low, that is, outcome for the basin no distinct surface-area drainage system ( river erosion ). The water discharging openings are mostly directly at the hem, at the breaking edge of a Polje, where the sediments abut the mostly steep rock formations. These breaklines also underground water channels of the water-bearing sediments are forced to overflow. These are the places where larger amounts of water come to light as karst springs.

Life and settlement in the karst

The discharge capacity of the ports varies, depending on the ( clogged ) bottleneck capacity. In the case of above-average or cyclically higher precipitation and / or blockages caused by underground collapses or foreign body in the water / were poljes for long, short or seasonal cycles in temporary lakes. In fertile soils a Polje these could feed on many people. However, the population density is traditionally low, as the hydrological control of poljes allows an expanding population through secured management only with the techniques of the last 100 years. Today, let reclamation by ditches, artificial discharges and dilatations come only in extreme cases to flooding. Sink-holes and large-scale departures may be provided with settling basins, rakes and funnels to stabilize the discharge capacity.

Hydrogeological poljes with a ( large ), several or many Ponor (s) are observed (Tripoli plateau, Peloponnese, 40x20km, 47 proven sink-holes of various sizes and activity).

Environmental problems in karst

The aquifer of poljes and other karst formations for drinking water supply in many European countries is of great importance. Of them, the infiltration of groundwater hazardous pollutants must be kept away. Amidst or populated at the edges, or crisscrossed by roads poljes ( eg Benaojan, Sierra de Libar ) provide a reservoir extent an increased risk of contamination is because their karst environment often has a thin to absent soil cover, high infiltration and flow velocities, and therefore a low retention capacity for groundwater pollutants.