The Krka river

Geographic position

The Krka River flows through the Dalmatian region, in the area of Šibenik-Knin County, between the plateau of the Čikola River and the Dalmatian Zagora region.

The mountain massifs Velebit, Dinara, Svilaja and Mosor rise up to the west, north and east. The river is bounded by a triangle of cities Knin – Zadar – Split, and its backbone is along the line Knin – Drniš – Šibenik.

The relief around the Krka River is marked by the wall of mountains to the north, formed by the Dinara, Uilica and southern part of Velebit, as well as valleys (Kninsko Polje, Kosovo Polje and Petrovo Polje), limestone plateaus (northern Dalmatian, Kistanje and the plateau around the Krka and Čikola Rivers) and the canyons of the Krka, Krčić and Čikola Rivers. Mt. Promina separates the valleys and plateaus.

The Krka springs at the foot of Mt. Dinara, 3.5 km northeast of Knin, just under the 22 m tall Topoljski slap. The river flows 72.5 km to its mouth in the Adriatic Sea near Šibenik. The upper 49 km of the course is purely freshwater, while the lower 23.5 km course is brackish. The total slope is 224 m. The freshwater course of the river is fed by five tributaries: Krčić (10.5 km), Kosovčica (12.5 km), Orašnica (5.3 km), Butišnica (39 km) and the Čikola with the Vrba River (37.8 km), while the submerged part of the mouth is fed by the Guduča River (7 km). The hydrogeological basin of the Krka River covers an area from 2500 to 2650 km2. The mean annual flow of the Krka River over Skradinski buk is approximately 55 m3/s, while the daily flow varies from 5 to approximately 565 m3/s.

Geological properties and the morphogenesis of the Krka River

Thanks to the constant process of travertine-building, the Krka River is a karst phenomenon and nature’s priceless gift to man.

The present day appearance of the Krka canyon is the result of tectonic movements and surface karst-building processes in the carbonate layers. Following the Würm period of deglaciation in the Pleistocene, the melting of the ice on Earth cause the sea level to rise, thereby submerging today’s Adriatic coast. At that time, the estuary of the Krka River, from Šibenik to Prukljan Lake, was formed.

With the formation of the travertine layers in the post-Würm period, the Skradinski buk, Roški slap and the remaining waterfalls began to rise along the river’s course, thus causing the formation of Visovac Lake and the remaining water accumulations in the canyon part of the present day river. The only man-made accumulation is Brljan Lake, which was created as a reservoir for the Miljacka hydroelectric plant.

Hydrogeological properties, springs and source of the water of the Krka River

The Kninsko polje, or Knin field, is the richest in water, with the spring of the Krka River at its edge, in a cave just under the Topoljski slap waterfall, at an altitude of 224 m.

The Krka River basin is made up of the basins of the Butišnica, Krčić, Kosovčica, Orašnica, Čikola, and Guduča Rivers as well as the basin of the Krka River, which is spatially the largest. In addition to these waters, the Krka River basin includes the waters of the sinkholes southeast of Grahovo in Bosnia and Herzegovina and the subterranean waters of the upstream reaches of the Vrba River valley, a tributary of the Čikola River.

There are three types of areas within the Krka River basin: mountains, fields and plateaus. The mountain region includes the northeastern part of the upper course of the Krka River. The fields include the middle course of the river, with four large fields: Plavno, Kninsko Polje, Kosovo Polje and Petrovo Polje. Kninsko Polje, or Knin Field, is richest in water, with the spring of the Krka River at its edge, in a cave under the Topoljski slap waterfall, at an altitude of 224 m.

The Krka River receives the majority of its tributaries in the first 4 km of its course, still in the Kninsko Polje. The first larger left tributary is the Kosovčica, and right tributary is the Orašnica. Downstream, after leaving Kninsko Polje, the Krka receives its richest tributary, the Butišnica. The Čikola River flows through Petrovo Polje, and becomes the final tributary of the freshwater part of the Krka River, draining just above Skradinski buk.

In the canyon part of the Krka River, the largest tributaries are Miljacka and Jaruga, while the Torak spring is an important tributary in the Čikola River canyon. The Miljacka spring, on the right bank of the Krka River, is a direct connection between the Zrmanja River and the Krka River, and is a unique hydrogeological phenomenon.

Downstream of Skradinski buk, the Krka River is under a maritime influence, and its springs are brackish. The only significant tributary in the lower, submerged part of the mouth of the Krka River is the Guduča River.

Treatment plant

Wastewater treatment plant was constructed on the left bank of the river at Skradinski Buk and became operational in 2006.

The Krka River within the borders of Krka National Park is categorised as a Category I watercourse. Considering that this is a very sensitive area, a wastewater treatment plant was constructed on the left bank of the river at Skradinski Buk. The plant has third degree treatment, which degrades organic matter by about 80% prior to the release of the treated water. The plant became operational in 2006.

After the construction of the treatment plant, the Public Institute of Krka National Park permitted the companies HEP d.o.o. and Vodovod i odvodnja d.o.o. to subsequently also connect to the plant, which enabled the treatment of the wastewater of all water users on the left bank of the Krka River at Skradinski Buk. The laws of the Republic of Croatia and the EU Directives (91/271/EEC) prescribe the quality standards for wastewater prior to its release into the natural environment (sea, rivers, etc.).

The functioning of the plant is controlled daily. Water leaving the plant is sampled and analysed by the Public Health Institute of Split-Dalmatia County. Water samples must correspond to the requirements stipulated by the water use permit and to the prescribed values for the water.

A treatment plant is defined as a water structure with facilities used to purify the wastewater from the public drainage system prior to its release into a natural receptacle. Its functioning uses biological procedures (the same as in the natural environment) with active silt, in which microorganisms (usually bacteria), degrade organic matter in the water while consuming oxygen. In this way, organic carbon is removed from the wastewater, the concentrations of nitrogen and phosphorous compounds are reduced and the silt is stabilised. The success of the aerobic process for the biological cleansing of wastewater depends on the concentration of organic compounds and the concentration of microorganisms. The products of the process are silt, gas and purified waste water.

The Public Institute of Krka National Park is also planning to construct treatment plants at Roški Slap and at the Puljani centre.

Climate

The Šibenik region is directly exposed to the sun’s rays, and is among the sunniest parts of Croatia.

The maritime influence on the Krka River valley penetrates deep inland, and significantly impacts the climatic regime in the upper river course and at the springs.

Further inland from the mouth, the maritime influence is weakened; as such, the mean annual air temperature at Šibenik is about 15oC and only 13oC at Knin. The mean air temperature in the coldest month (January) is about 7oC at Šibenik and 5oC at Knin, while in the hottest month (July) it is about 25oC at Šibenik and 23oC at Knin. The highest air temperature ever recorded was 39.2oC at Šibenik and 39.6oC at Knin, while the lowest air temperature recorded was -10.2oC at Šibenik and -18.3oC at Knin. Just over 100 clear days and about 90 cloudy days can be expected per year.

The Šibenik area receives about 2600 hours of sunshine per year, while the Knin area receives about 2400 hours, and these are among the sunniest parts of Croatia. The annual amount of precipitation is about 809 mm in Šibenik and about 1078 mm in Knin, with the majority of precipitation falling during the colder part of the year from October to February. The least precipitation falls in summer, particularly in July, when only about 30 mm falls in Šibenik and 46 mm in Knin. Snow is a rare occurrence in this area, particularly in the coastal area. The mean relative humidity is 57% in Šibenik and 67% in Knin.

During the colder part of the year, the Krka River valley is exposed to north-easterly (bora) and south-easterly (scirocco or jugo) winds, where the bora wind is prevalent throughout the entire area, while the jugo wind usually only blows in the lower course of the Krka River. In summer, a gentle, daytime westerly (mistral) or south-westerly breeze develops on clear days.

– See more at: http://www.np-krka.hr/stranice/climate/85/en.html