How it all began

Although the Krka River and its landscape seem eternal, the birth of the river and the formation of karst, the creation of the plateau, the cutting of the canyons, and the construction of the travertine barriers lasted for eons, leaving traces today from which the geological past of the area can be read. 

The hard rocks surrounding the Krka River were once seabed.

This sea was part of the ancient Tethys Ocean that the Dinarides rose from. The Dinarides mountain range is primarily built of carbonate rock (limestone and dolomite), created by the deposition of seashells through the eras of the Mesozoic that included the Triassic, Jurassic and Cretaceous periods.

The water solubility of carbonate rock is perhaps the most important condition for the karstification process. In essence, this is a chemical process that has taken place for millions of years, and is still ongoing. Water corrodes the carbonate rocks, creating fissures, which make it impossible for the rock to retain water. Both tectonic and mechanical processes play a part in this process. The present day appearance of the Krka Canyon is the result of tectonic movements, and superficial karstification processes in the carbonate deposits of Mesozoic and Tertiary age. From the rocks surrounding the Krka River, we can read their geological timeline. If the limestone layers that we see on the canyon walls are of varying composition, purity and thickness, then we know that they settled under differing conditions, and the position and types of deposits explains how the sea surface rose or fell.

Hollowness and fissures are the main features of the rock of karst landscapes. This leads to the formation of numerous pits and caves. The karstification process is also responsible for the formation of the ornamentation within these structures. Under special conditions, it is possible that this process is reversed: where calcium carbonate is again secreted, and instead of wearing, the rock grows. That results in the formation of stalagmites and stalactites, as well as travertine (tufa), the fundamental phenomenon of Krka National Park.

Like the sight of living water flowing through its opposite, hard rock, so too is the dual nature of karst: rugged, and yet so vulnerable to pollution, which can easily enter the groundwater due to the permeability of the rock. However, this is also its value, as the constant two-way circulation of water creates a diversity of habitats on the surface and underground, ensuring living conditions for so many different species, including rare, threatened and endemic species.

Now that we know what karst is, it is easier to understand the eons that it took for the Krka River to be born and to grow, creating the plateaus, cutting the canyons and raising up the travertine barriers. Karst here is the main feature: in addition to creating the landscape around us, it has also defined the way of life for the people living here. The karst regions of Croatia, which forms an uninterrupted belt 50 – 100 km wide along the entire Adriatic coast, covers about 46% of the nation’s land territory. It is our duty and responsibility to protect it, so that our future generations can also read their history from its rock.

The geological formation of the Krka River region began with the sedimentation of limestone and continued with the formation of the plateau.

The plateau of the Krka River was formed at the end of the Pliocene and beginning of the Pleistocene, while its canyon was cut into relief in the late Ice Age. What man counts in millions of years, and divides into eons and epochs, is only a moment for the Earth. In geomorphological terms, three sections of the Krka River basin can be distinguished: the mountainous area in the northeast, where the Krka tributary valleys are deeply cut, the plain in the central part with a pronounced hydrographic network with numerous springs, and the North Dalmatian plateau.

Like the entire relief of the Krka River, its plateau forms a special karst shape. Above and below it is hard limestone. Its characteristic is that it is equally balanced regardless of changes in the composition of the rocks, and that it gradually rises towards the mountainous part. If we try to imagine the area of the Krka River at the turn of the Pliocene to the Pleistocene, when the plateau was formed, and later in the late Pleistocene, when its canyon was formed, it is necessary to keep in mind the great changes in climate and the relationship between land and sea. From the geoclimatic conditions of that time, some scientists predict the future of the Earth and its inhabitants.

To illustrate the period, in the Strmica clay pit in a small village north of Knin through which the Krka River tributary of Butišnica flows, in the 1970s the bones were excavated of a southern elephant that did not have fur that had lived during the Lower-Middle Pleistocene, some 700,000 – 2.6 million years ago, when the climate was much warmer than it is today. Bones were also gathered of an Upper Pliocene - Lower Pleistocene ancestral elephant and a Lower Pleistocene warm climate rhinoceros. One canine tooth was found belonging to a Panthera toscana, a beast similar to today's leopard, along with one canine of a Lower Pleistocene bear (Ursus etruscus). The finds were described by Mirko Malez, a Croatian geologist, speleologist, and paleontologist, known as the pioneer of Croatian speleo-archaeology, and were interpreted for us by Drazen Japundžić, Head of the Geological-Paleontological Department of the Croatian Museum of Natural History. Part of the collected material is stored in the Department of Quaternary Geology and Paleontology at the Croatian Academy of Sciences and Arts. Pantheri toscani, zvijeri sličnoj današnjem leopardu, i očnjak donjepleistocenskog medvjeda (Ursus etruscus). Nalaze je opisao prof. Mirko Malez, hrvatski geolog, speleolog i paleontolog, poznat kao pionir hrvatske speleoarheologije, a nama ih je protumačio Dražen Japundžić, voditelj Geološko-paleontološkog odjela Hrvatskoga prirodoslovnog muzeja. Dio prikupljene građe čuva se u Zavodu za geologiju i paleontologiju kvartara pri Hrvatskoj akademiji znanosti i umjetnosti u Zagrebu.

Several theories exist about the formation of the plateau. The fluvial theory assumes the existence of a large, wide, and slow river in the geological past, when the climate was wetter and water more abundant, which eroded the limestone rocks of the initial relief. The slope of the terrain from the hinterland to the sea would be in favor of this. According to another theory, called abrasion, the plateau was formed by action of the sea, which gradually receded. There is also a theory that connects the previous two and interprets the formation of the plateau to simultaneous action of the sea and continental fluids (fluvial-abrasion theory). The corrosive theory explains the plateau formation in the area around the Krka through the complex interaction of erosion, leaching, and corrosion of the limestone in the warm and humid paleo-climatic conditions that prevailed 3 million years ago. Scientists and researchers also cite a tectonic theory, according to which the plateau was formed by varied local uplifting and twisting of the Earth's crust, and along the breaking faults the plains and river valley (canyon) were formed.

As a result of intense Late Pleistocene glaciation, the canyon of the Krka River was cut into the plateau along tectonic and lithological predisposed directions.

Cut deep into the North Dalmatian karst plateau, the Krka River Canyon is special for many reasons, not just its beauty.

The world's largest and best known canyon is the one in Arizona, that was carved out of stone by the Colorado River over millions of years – the Grand Canyon. The second deepest canyon in the world, and the deepest in Europe, is the Tara River Canyon in Montenegro. Cut deep into the North Dalmatian karst plateau, the Krka River Canyon is special for many reasons, not just its beauty. It is the youngest part of the landscape. The remainder is raised travertine barriers, which has given this area a unique appearance that is recognisable worldwide.

To simplify geomorphological factors, we could say that a crack was formed in the Earth’s crust from the Dinara Mountains to the sea, where the surface waters flowed. However, the formation of the Krka River Canyon was the result of much more complex processes and tectonic movements. The cutting of the river into the plateau was monophasic, meaning that the canyon was not formed gradually over time, but all at once, as seen by the lack of river terraces along its course. The initial relief was the first factor to modify the original watercourse, and then the watercourse was determined by tectonic movements and the composition of the rock. This is seen in the breakage lines and light bending of the land that favoured the erosion action of the river. At that time, the Krka had more water and carried more rock downstream, blazing its path towards the sea, which due to lower sea levels was much farther offshore than the present day coastline. This is why we can follow the ancient Krka Canyon all the way to the southern coast of the island of Zlarin in the Šibenik archipelago. All these events took place during the glacial period (Upper Pleistocene - Würm, 40,000 to 170,000 years ago).

The Early Holocene followed the Würm glaciation on the geological timescale. During this era, the glacial ice massively melted, raising the sea level by 120 to 125 metres. This took place about 18,000 years ago, when the Krka River estuary was formed from Šibenik to Prukljan Lake. Further increases in sea level brought the sea right up to Skradinski buk. Today, the Krka River estuary is considered to begin under the Skradinski buk waterfall and extends southwards to the Fortress of St. Nicholas, 22 kilometres downstream. Within the estuary lie the towns of Skradin and Šibenik, and picturesque places such as Zaton and Raslina, sites where notable cultural and historical heritage was formed in unity with nature over a thousand years. During this time, the Krka has flown on the sea surface. How this eternal intertwining of freshwater and sea water will change in the future, will be seen in the Earth’s geological future. Numerous scientists believe that the interglacial period has not yet reached its maximum and that sea levels will continue to rise, caused by the anthropogenic activities and the greenhouse effect. As we sail upstream from Skradin to Skradinski buk, we should all consider how, for the first time in the many eons of the Earth’s long history, humans are now affecting natural processes. Because the water remembers.

After the karst, limestone rock rose up out of the ancient sea, flattening the surrounding lands and cutting a deep canyon, the Krka River waterfalls were formed, thus creating the present day appearance of the river bed, and the characteristics of the living world. The waterfalls are the youngest formations in the canyon.

The travertine building process began in the Pleistocene, and has continued to the present day, with some interruptions. At the end of the last glacial age called Würm, the climate became warmer, water flow slowed and the conditions were created for the colonisation of algae, mosses and other organisms that take part in the travertine building process. In the Krka River Valley and its tributaries, the Pleistocene travertine is found up to 20 metres higher than today's riverbed, which tells us of the level at which the water flowed during that time. This travertine is called fossil travertine.

The majority of the travertine at the waterfalls is less than 10,000 years old. With the creation of travertine deposits in the post-Würm period, Skradinski buk, Roški slap and the other waterfalls began to rise up above the water level, creating Visovac Lake and other accumulations in the canyon sections of the present-day Krka River. The travertine forms differ in their age. The youngest travertine formations are the thresholds that form under the water surface. There are also barriers, travertine curtains, cones and many other forms. In terms of the structure and size of travertine barriers, we know that the most travertine is deposited near the end of the river course, where the water flow rate was slower. Skradinski buk waterfall is the longest travertine barrier on the Krka River and in Europe.

Travertine is also called tufa. This is the name for calcium carbonate (limestone) that settles out of running waters onto various types of substrates. Travertine will settle only in waters that have sufficient quantities of dissolved calcium bicarbonate. The waters in karst are rich in this mineral, as karst landscapes are made up of limestone and associate rock, which together are called carbonate rocks. They are easily dissolved and create very strange forms, both on the surface and underground. In order for these chemical processes to unfold unhindered, temperature, water flow rate, pH value of the water, dissolved oxygen concentrations and the organic matter content in the water are also important variables.

The travertine building process requires travertine building organisms, which are aquatic algae and mosses upon which these minerals settle. Without them, the calcium carbonate would not be retained, as it would be washed downstream, especially in places where the water flows quickly, mostly at sites with an uneven river bottom. The slope and structure of the riverbed are not uniform at any of the waterfalls, meaning that today we can enjoy the uniqueness of each.

The travertine growth conditions are most favourable in the present day, and this process can be seen along the entire course of the river, with new travertine deposits being continually formed on the Krka River, which make new waterfalls. However, it should be stressed that travertine is highly sensitive to water pollution and increase concentrations of organic matter in the water.

Therefore, our primary function is to preserve the travertine barriers as vulnerable parts of the natural system, and to ensure the water and surroundings areas are clean.

The hydrography of karst regions is full of surprises.đenja. Putovi kojima teku podzemne vode i brojni načini na koje su povezane ili razlozi zašto to nisu izazov su istraživačima spužvastog podzemlja krša. Krka, u toliko aspekata fenomen krša, nije, ni kada govorimo o njezinu izvorištu, iznimka.

The routes taken by underground water and the many ways in which they are connected, or the reasons why they are not, represent a challenge for researchers into the karst sponge-like underground. The Krka River, in so many ways a karst phenomenon, is no exception, even when discussing its source.

The source of the Krka River is a spring in a cave at the foot of the Krševac hill, 3.5 km northeast of the city of Knin. The spring is assigned to the Vaucluse type, named after the town of Fontaine-de-Vaucluse in southern France. It is characterized by its inexhaustable water, but with strong fluctuations noted throughout the year. The source of the Krka River consists of three permanent springs: the Main Spring, the Small Spring, and the Third Spring.

The main source is in a cave (siphon) below the 22 m high Topoljski buk waterfall at an altitude of 224 m above sea level. The Third Spring and the Small Spring are located on the left bank of the Krka River, the first 50 m, and the second 150 m downstream from the waterfall. The Third Spring gives about 3 - 5% of the total waters from the Krka springs, the Small Spring about 10 - 15%, while the most abundant is the Main Spring, with about 80 - 95%. The flow from the Main Spring ranges from 1.5 to 10 m³ / s.

But what makes the source of the Krka River interesting and unique is the Krčić waterfall, Topoljski buk, or the Great waterfall, which falls from 22 meters in height and flows into the Krka River spring. The course of the Krčić River ends with the Topoljski buk waterfall, and the waterfall itself is the mouth from which it flows into the source of the Krka River at its base. The main, inexhaustible Krka spring is visible only in summer, when the riverbed of the Krčić dries up and the Topoljski buk waterfall lacks water. If you visit in winter, the Krka spring is completely covered by the waterfall from the Krčić – and there is no trace of the source of the Krka. In the morphogenetic sense, the Krčić is the source of the Krka River, and today represents its first tributary. It originates at the base of the Dinara Mountain, to the west of the village of Kijevo, at an altitude of 375 m asl. It is 10.5 km long. During heavy rainfall or snowmelt in the mountains in the hinterland, the Krčić is an unbridled torrential river, while it dries up completely in summer. If it did not dry up in summer, then the Krčić would not even exist as a separate entity, and the source of the Krka would be considered to be where the spring of the Krčić is today, at the foot of the Dinara Mountain, which oral folk tradition claims is where the Krka River is born. Nonetheless, people recognized the seasonal water levels of the Krčić and called it by its current name (“Small Krka”). In the recent geological past, due to a colder climate and more precipitation, it did not dry out, so the Krka and Krčić formed a single course. This is shown by the remains of abundant travertine deposits in the Krčić valley high above the present day current. The complex geological conditions of this area are the cause of complicated hydrological relationships. Strong karst springs are related to the influx of groundwater from the mountainous Dinara area and its hinterland in the territory of the neighboring state of Bosnia and Herzegovina (Biondić and Biondić, 2014), while tracing underwater courses has shown that the Dinara Mountain does not represent an obstacle to groundwater movement.

A tributary is any river or stream that drains into another flowing body of water, and not directly into the sea or a lake.

The Ohio and Missouri Rivers in North America, both large rivers, are actually tributaries of the Mississippi River. The Krka River receives five tributaries in its freshwater part: Krčić (10.5 km long), Kosovčica (12.5 km), Orašnica (5.3 km), Butišnica (39 km) and Čikola with the Vrba River (37.8 km), while in the submerged estuary of the river, it receives the Guduča River (7 km).

The Krka River begins where the Krčić River ends. In the morphogenetic sense, the Krčić is the source of the Krka River, and today is considered its first tributary. It springs in the foothills of the Dinara Mountains, west of the village Kijevo, at an elevation of 375 metres. It flows for 10.5 km. During heavy rains or snow melt in the mountains inland, the Krčić becomes a torrential river, while during the summer months, it dries out completely. In the recent geological past it did not dry out, as the climate was cooler and there was more precipitation, making the Krčić and Krka one flowing waterbody. This can be seen the remnants of the many travertine deposits in the Krčić Valley, high above the present day course of the Krka river. paludi. Zbog toga se nametala potreba regulacije gornjeg toka rijeke Krke i melioracije okolnih krških polja. Prvi znatniji lijevi pritok rijeke Krke jest Kosovčica, koja dovodi vode nekoliko stalnih ili povremenih izvora s istočnog oboda polja, a desni Orašnica, koja glavninu vode dobiva od Crnog vrela i izvora u Vrpolju. Nizvodno od ušća Orašnice u Krku, nakon što napusti Kninsko polje, s desne strane utječe rijeka Butišnica, njezin najizdašniji pritok, s protokom od 2 do 20 m³/s i površinom slijeva od 225 km². Butišnica izvire iz nekoliko izvora kod sela Kaldrme, u planinskom području u najsjevernijem dijelu slijeva rijeke Krke. Za Prvog svjetskog rata nasipom je odvojena od Krke pa rijeke sada teku paralelno do svog spoja tako da je „prirodno“ ušće kod Bulinog kuka pomaknuto oko dva kilometra nizvodno.

In the Kninsko Polje and Kosovo Polje fields, the Krka receives several calm tributaries: Butišnica, Orašnica and Kosovčica. On the earliest maps, from the period of establishment of Venetian rule in this region, the area under the Knin fortress, where the Krka and Kosovčica meander, once formed a wide wetland belt that was marked as a paludi (marshland). With time, the need arose to regulate the upper course of the Krka River and to allow for amelioration of the surrounding karst fields. The first significant left tributary of the Krka River is the Kosovčica River, which carries the water of several permanent and temporary springs rising along the eastern edge of the field, while the right tributary is the Orašnica, which receives most of its water from the Crno Vrelo (Black Spring) and other springs in Vrpolje. Downstream of the mouth of the Orašnica, once the Krka leaves the Kninsko Polje field, its largest tributary enters on the right side, Butišnica. The Butišnica River springs from several sources near the village Kaldrma, in the mountainous areas of the northernmost parts of the Krka River catchment. This is the most water-rich tributary of the Krka, with a flow rate of 2 to 20 m³/s and a catchment area of 225 km². During World War I, it was separated from the Krka by an embankment, and so now the two rivers flow parallel until their confluence, such that the “natural” mouth at Bulin Kuk was shifted about 2 kilometres downstream.

The Čikola River runs through the Petrovo Polje field, and this is the final and largest tributary in the freshwater part of the Krka River. It flows from its source in the foothills of Mt. Svilaja to its confluence with the Krka under Skradinski buk, and this river is part lowland and part canyon river. In the literature data, the length of the Čikola varies from 39 to 47 km, while the catchment basin covers an area of 836.8 km². During wet winters, the river is full of water and floods part of the field, while in the summer months, the water levels are very low due to drought and use of the river water to irrigate the fields, and therefore its central section often dries out. Throughout the entire 19th century, the locals faced the issue of how to regulate the flow of the Čikola River due to flooding of the fields, destruction of crops and the spread of malaria. The final tributary of the Krka, the Guduča River, is an extension of the course of the Bribišnica stream, which springs on the western side of the hill Bribirska Glavica. Near the bridge in Lađevci, the Bribišnica stream becomes the Guduča River, and flows over the next 7 kilometres to Prukljan Lake. The upper course often dries out, while the lower course is a submerged valley. The lower course and mouth of the Guduča River is an area characterised by the wetland vegetation, rich and diverse flora and fauna, and exceptional pleasing landscape.

The Krka River is bounded by mountains on three sides – Mt. Velebit to the west, Mt. Dinara to the north and Mts. Svilaja and Mosor to the east.

The relief around the Krka River is marked by the wall of mountains to the north, created by Mts. Dinara and Uilica and the southeastern end of Mt. Velebit, the valley depressions (Knin polje, Kosovo polje and Petrovo polje fields), limestone plateaus (northern Dalmatian, Kistanje and the plateaus surrounding the Krka and Čikola Rivers) and the canyons of the Krka, Krčić and Čikola Rivers. Between the valley depressions and the plateaus lies Mt. Promina.

The mountains around the Krka River belong to the Dinarides mountain range and were created some 20 to 30 million years ago. Their tectonic evolution began with the subduction of the African plate (Adriatic microplate) under the Eurasian plate, as a result of the breakdown and shifting of the palaeocontinents Gondwana and Laurasia. During the time of the settlement of the first deposits in the present day area of the Krka River, the Dinarides region was part of the vast Tethys Sea. In general, the entire Dinarides area, in which the Krka River Canyon was cut, arose from the subduction of the African plate (Adriatic microplate) under the Eurasian plate, following the breakdown and shifting of the palaeocontinents Gondwana and Laurasia. During the time of the settlement of the first deposits in the present day area of the Krka River, the Dinarides region was part of the vast Tethys Sea. The collision of the African plate with the European one, which began at the end of the Cretaceous period about 65 million years ago and is still ongoing today, caused the sea to shrink and was characterised by intensive tectonic movements. Layers of rock, originally settled on the seabed, were folded, broken and raised up above the sea level, creating massive mountain chains such as the Alps and the Dinarides.

In his paper Polja gornje Krke [Fields of the Upper Krka], professor Mladen Friganović leads us around the upper Krka River, in the transition area between the mountainous inland and the coastal belt. The valley depressions (Knin polje, Kosovo polje and Petrovo polje fields) lie almost in line with the parallels; and are closed off by Mt. Dinara (elevation 1831 m) and Mt. Svilaja (1509 m) to the east, while to the west is the limestone plateau extending all the way to the southeastern end of Mt. Velebit and the Bukovac hills. Northeast of the Knin Polje field is the dominating limestone massif, Mt. Dinara and its foothills. Mt. Dinara is a bordering mountain between Croatia and Bosnia and Herzegovina, with the side facing westwards belonging to the Dalmatia region of Croatia, and the side facing east falling within the borders of Bosnia and Herzegovina. The highest peaks of Mt. Dinara overlook Peručko Lake and the view extends all the way to the Triglav Mountains in Slovenia, and the neighbouring mountains Svilaja and Promina, filling the horizon around the Krka River.

East of the Knin Polje field is the Krčić Valley, which is collected with the valleys under Mts. Dinara and Svilaja. Both to the east and west of the Knin Polje field lies the limestone plateau into which the Krka has cut its path. On both side of the southern part of the Kosovo Polje field, the plateau narrows and suddenly shifts into the steep limestone slopes of Mts. Kozjak and Promina. Around Petrovo Polje field, the plateau is most pronounced and widest to the east, where the gently rolling “Podi” foothills rise up to meet the slopes of Mt. Svilaja. At the western edge of the field rises Mt. Promina (1148 m), a typical example of an island formation. Mt. Promina is bounded to the west by the Krka River Canyon, to the south by the Čikola River Canyon, and to the east by the Petrovo Polje field. Mt. Promina dominates the surrounding lower areas, and provides lovely views to the south of the Miljevci plateau and the Krka and Čikola Rivers, and from the peak it is possible to see the Adriatic Sea and islands, some 30 km away.

The Krka and its tributaries Orašnica and Butišnica from the right side and Kosovčica on the left side runs through the Kninsko Polje field. The Čikola River with its tributary Vrba and their occasional small tributaries run through the Petrovo Polje fiel

The landscape of the Krka River is marked by three different types of relief: the mountainous area to the northeast, the Northern Dalmatian plateau with its canyons, and the lowland expansions or fields. These karst fields, called polje, are the largest karst depressions. They typically have a flattened bottom through which a watercourse usually runs. In open fields, such as the Kninsko Polje field, this water course flows out of the field through a deep canyon, while most karst polje fields, as a rule, are closed in on all sides with water courses springing along the edges, such as the Lika River in the Ličko Polje field (N. Bočić). In the Krka River basin, we find three fields: Kninsko Polje, Kosovo Polje and Petrovo Polje. Their valleys lie almost perfectly aligned with the parallels over a length of 41 km. To the east, they are closed off by Mts. Dinara and Svilaja, to the north they continue into the deep Butišnica valley, while to the west is the limestone plateau extending from the southeastern slopes of Mt. Velebit and the Bukovac hills. The Krka and its tributaries Orašnica and Butišnica from the right side and Kosovčica on the left side runs through the Kninsko Polje field. The Čikola River with its tributary Vrba and their occasional small tributaries run through the Petrovo Polje field. Professor Mladen Friganović in his book Polja gornje Krke (Fields of the Upper Krka; Zagreb 1961), gave us a detailed description of all the karst forms found here, and the life contained within Polja gornje Krke, već je 1961. dao detaljan opis tih oblika u kršu i života u njima. 

There are two theories about the formation of these fields. One is based on a theory of tectonic genesis, the second on tectonic predisposition, after which the landscape was shaped through external processes. They were shaped in the zone of contact between the Adriatic and Dinaric megastructural units of the karstified Dinaric region. These three fields share a common feature in that the surface water running through them drains into deeply cut canyons, and their watercourses are fully dependant on precipitation. Pluvial or rain river regimes are most prominent in the Petrovo Polje field. In the past these fields were widely flooded in winter, with very little water in summer, making economic development difficult, as the local economy was based on the cultivation of the fields and the many mills driven by water power. These oscillations were particularly felt by the town of Knin. Therefore, the need arose to perform engineering works to regulate the supply of water.

The smallest of the fields is the Kninsko Polje. It was first mentioned in the year 1050, as Tenin campum. With the Golubica area, it covers 24,2 km² and has the least defined shape. It is separated from the Kosovo Polje field by the Horse’s Head hill and Burnum ridge, and between these the Kosovčica River has cut its path. The bottom of the field is composed of two floodplain plateaus, the Krka to the east and Butišnica to the west, which are separated by a series of hills. On the southern edge of the field the Spas limestone ridge rises up, and under it is the town of Knin. The Kosovo Polje field is right in the middle of these three fields, in terms of its position, size and elevation. It covers an area of 33.8 km² and is elongated in the direction of the parallels, like the Kninsko Polje field. It stretches over a length of 13.5 km from Burnum to Tepljuh. The largest field is Petrovo Polje. It is shaped like an isosceles triangle, with the base lying along the southeastern edge of Mt. Promina and peak at the confluence of the Vrba and Čikola Rivers. This field is 17 km in length and covers an area of 57 km², making it the largest and most connected alluvial plain. It was previously called Campus Illyricum while the present-day name was first mentioned in the 11st century, likely under the rule of Croatia’s last king, King Petar Svačić, and named after the Petrovac hill fort that once stood on the northern edge of the field, which the king built and occasionally inhabited.

The Krka is a paradox of the bare and hard limestone and karst permeable to water and increasing drought, and the soft and green dolomite rock with the fragile marl in the depressions. The Krka is a combination of the bura and jugo winds, the coastal belt

In the area of this one river, the climate also has two faces. The Krka River runs from Knin to Šibenik, and the climatic characteristics are analysed on the basis of data from climate stations situated in those two towns. With an average of 2647 hours of sunlight per year in Šibenik and 2377 hours in Knin, the area of Krka National Park is amongst the sunniest parts of Croatia.

In the Krka River valley, the maritime influence penetrates deep inland, significantly affecting the climate conditions throughout the entire park area. The paleoclimatic conditions were important in shaping the relief, particularly the valley depressions, during the alternating glacial and interglacial periods. During warmer periods, travertine barriers were created and the river expanded into lake-like sections upstream, thus reducing the process of erosion. On the other hand, during colder periods, especially glacial periods, when the quantity of precipitation increased and temperatures dropped, fluvial erosion was increased. In the middle of the glacial period, there was about 20% more precipitation and temperatures were 4 to 5°C colder than they are today. The second half of the glacial period was marked by a reduction in precipitation (about 20% lower than today’s values until 20,000 years ago) due to the accumulation of ice in the Dinaric region and the lowering of air temperatures (to about 12°C lower than the present day values).

According to the Köppen classification, the climate in the area of Krka National Park has been classified as Csa, indicating a moderately warm, Mediterranean wet climate, with dry and hot summers. The area of Krka National Park experiences all four seasons. Winters have more cloud cover and precipitation, while summers are clear and sunny. The mean annual air temperature in Knin is 13°C, two degrees less than in Šibenik, due to the influence of the sea. The mean air temperature in the year’s coldest month, January, is about 7°C in Šibenik and 5°C in Knin, while in the warmest month, July, mean air temperature is 25°C in Šibenik and 23°C in Knin. Due to the maritime influence, which is slow to cool, autumn is warmer than spring. There is little likelihood of very low temperatures.

The proximity of sea and surrounding mountains affect the quantity of precipitation. The most precipitation occurs during autumn and winter, with a third of the total annual rainfall between October and December. During this time, the rivers are heavy with waters. The least rain falls in summer, especially July. Snow is very rare in this area, particularly along the coast.

In addition to being the sunniest, the Krka National Park area is also among the area with the clearest skies in Croatia. Spring is sunnier than autumn, and the least sun is seen in December and January, when the days are shortest with the most cloud cover. The winds of the colder seasons dominate in the Krka River valley: the northwesterly bura (bora) and the southeasterly jugo (scirocco). The bura wind is pronounced throughout the entire park area, while the jugo is strong only in the lower reaches of the Krka River. In summer, the light, daytime, westerly or southwesterly wind called the maestral (mistral) blows on clear days.

*Mladen Friganović, Rijeka Krka: od antičkog Titiusa do nacionalnog parka

Izvor: Perica, Orešić, Geomorfološka obilježja doline i poriječja rijeke Krke s osvrtom na dio od Knina do Bilušića buka, 2005.

The Krka River, however, flows above the level of fluctuations of the karst underground watercourses, as a floating river that is not lost on such a substrate.

Water that flows then sinks, the intricate and interconnected underground passages sharing these waters, that then spring again – these are the distinctive properties of karst. The Krka River area is no exception, indeed, 72.5 km of river flowing through the waterless karst is a natural phenomenon. The waters of the Krka River are completely fresh for the first 49 km of the river’s course, while in the remaining 23.5 km, the influence of the sea is evident. With its tributaries, the aboveground catchment covers an area of 2450 km², while the hydrological catchment covers an even larger area, 2650 km². The total drop in elevation is 224 m. Karst regions are characterised by a complete lack of water, dominated by the carbonate rock. Their tectonic fracturing means that all atmospheric water quickly sinks underground. The Krka River, however, flows above the level of fluctuations of the karst underground watercourses, as a floating river that is not lost on such a substrate. The dynamic and direct connection between the surface and underground water flows is a special feature of karst, creating different habitats, transferring nutrients, and enabling life both above and below ground. That is why preserving the sensitive karst ecosystem is of the utmost importance.

Complex geological conditions are the reason behind these complicated hydrological relationships. Two megastructure units meet in the area of the Krka River: the Dinaric and Adriatic. The Dinaric carbonate platform is the site of the mountainous part of the Krka River basin, to the tectonic zone of Strmica–Knin–Petrovo Polje field, while the protected section of the canyon lies on the Adriatic carbonate platform. Of all the carbonate deposits, the majority are water permeable, allowing surface water to sink into the karstified relief. Only a smaller portion is water impermeable rock, forming a barrier for the underground watercourses. The zone of impermeable rock is situated in the source area of the river around Knin, and north of this, where we find the springs, as aboveground and underground watercourses that “feed” the canyon section of the Krka River. The southernmost karst spring in this zone is the Čikola spring in the Petrovo Polje field. During dry periods, it has no waters, while during rainy weather, it forms a river. The zone of impermeable deposits, or flysch, extends along the southern border of the park, around Skradinski Buk, to the Torak spring at the confluence of the Čikola and Krka River, and encompassing the lower part of Visovac Lake. The Krka is also fed by underground water sources. A part of those waters flow from the inland areas of Mt. Dinara (Grahovo Polje field), while a part comes from the upper catchment of the Zrmanja River, with which the Krka shares an underground water profile. The most abundant springs along the Krka River Canyon are Miljacka and Jaruga, while in the Čikola River canyon, this is the Torak spring. The Jaruga Spring is downstream of Skradinski Buk, while the brackish spring Litno is found in Zaton in the downstream Prukljan Lake section of the river.

The Krka River catchment receives about 1250 mm of precipitation per year. The most rain falls during the winter, while the summers are very dry. The water levels in the river are highest in November and March, and lowest in August. The mean flow rate in the river at the spring is 12 m³/s while at Skradinski Buk it is 55 m³/s. The highest ever flow rate, 481 m³/s, was recorded on 24 December 1982, while the lowest, 4.99 m³/s, on 5 October 1961. The highest water temperature recorded was 27.5°C at Skradinski Buk, recorded on 25 August 2011, while the lowest was 3.5°C, recorded on 12 January 1985. The highest water level at Skradinski Buk, 223 cm, was recorded on 7 December 2005, while the lowest, just 5 cm, was recorded on 3 October 1990.