The hydrography of karst regions is full of surprises. 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. 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* , while tracing underwater courses has shown that the Dinara Mountain does not represent an obstacle to groundwater movement.
*Biondić, Božidar; Biondić, Ranko: Hydrogeology of the Dinaric Karst in Croatia, Geotehnički fakultet, Varaždin, 2014.