The land of the Pivka intermittent lakes
Upper Pivka basin is a one-of-a-kind classical karst landscape along which the Pivka river flows, and it is further enriched by the intermittent lakes of Pivka, an exceptional karst phenomenon.
Upper Pivka basin is a one-of-a-kind classical karst landscape along which the Pivka river flows, and it is further enriched by the intermittent lakes of Pivka, an exceptional karst phenomenon. More than half of the municipality is within the Natura 2000 area, which reflects the presence of many natural values, the Natura 2000 area, and the Nature Park.
Characteristics of individual lakes
1. 1. Šembijsko jezero Lake
Šembijsko jezero Lake is the southernmost lake on Upper Pivka; its waters flow into Podstenjšek, a right tributary of the river Reka, from which it separates from the other Pivka lakes in the Pivka river basin.
A large shallow Nariče basin with a flat bottom is located in the immediate vicinity of lake Šembijsko jezero Lake. When the water level is extremely high, it flows down the stream into the lower-lying lake Šembijsko jezero Lake.
2. Bačko jezero Lake
Bačko jezero Lake is located to the north of the village of Bač. A stream flows from higher-lying Laneno jezero Lake and fills Bačko jezero Lake along extremely high waters.
3. Laneno jezero Lake
Laneno jezero Lake is the highest lake on Upper Pivka. Locals claim that flax was once grown in the valley where the lake is located, hence the name – Laneno jezero Lake.
4. Veliki dol za Kalcom
Veliki dol za Kalcem is located in a larger sinkhole next to Kalc Castle. South of it lies a shallow sinkhole that, on occasion, turns into a lake.
5. Kalsko jezero Lake
Kalsko jezero Lake is deepened into a terrace by a drainage ditch, from which the karst basin at Knežak descends into the valley of the river Pivka at its source.
6. Kljunov ribnik
Kljunov ribnik, which isn’t really a pond because there aren’t any fish in it. Olm or proteus, on the other hand, have been “thrown” to the surface on several occasions. It is the smallest lake, right next to the Pivka river’s bed, which flows just a stone’s throw away.
7. Malo Zagorsko jezero Lake
Malo Zagorsko jezero Lake is frequently seen because it runs parallel to the Pivka riverbed.
8. Veliko Zagorsko jezero Lake
Veliko Zagorsko jezero Lake is less frequently filled than Malo Zagorsko jezero Lake because it lies slightly higher.
9. Veliko Drskovško jezero Lake
Veliko Drskovško jezero Lake is the third largest of the Pivka lakes. It appears frequently because it lies on a similar plane as the Pivka river’s bed. In the centre, there is an islet with a hunting lodge.
10. Malo Drskovško jezero Lake
Malo Drskovško jezero Lake most likely receives water underground from Veliko Drskovško Lake. Malo Drskovško jezero Lake’s basin resembles a classical overflow karst polje with a spring and abyssal cave.
11. Parsko jezero Lake
Water flows into Parsko jezero Lake from Malo Drskovško jezero Lake, which lies only a metre higher. It flows beneath the surface into the Mišnik spring, which was once a particularly important spring because it powered a sawmill and a mill.
12. Radohovsko jezero Lake
Radohovosko jezero Lake is the only lake on the Pivka river’s left bank. It originates at the base of Primož and flows underground into Pivka.
13. Klenski dol Lake
Klenski dol Lake is located in the village of Klenik. When it is not present, there are some fields in the “valley” that have survived to this day among all the Pivka lakes.
14. Palško jezero Lake
Palško jezero Lake is the largest of all Pivka lakes. It is located north of Palčje and two kilometres from the Pivka riverbed. The basin is 1.5 km long and 0.5 km wide with a flat bottom. When the water level rises above 552 m, the lake also has two bays, Njivce and Ždink. Water from Palško jezero Lake flows underground to Trnje karst springs.
15. Petelinjsko jezero Lake
Petelinjsko jezero Lake is located in an oval basin at the foot of hill Okroglek. Because it is the lowest-lying lake, the water stays in it for the longest period of time. In terms of size, it is the second largest of the Pivka lakes. The water from Petelinjsko jezero Lake flows underground into the Žeje karst springs and then into the Pivka river.
16. Krajnikov dol Lake
Krajnikov dol Lake is located to the south of Jeredovce Lake.
17. Jeredovce Lake
Jeredovce Lake is the northernmost lake in the Pivka lakes group. They were once a very fertile area, but farming was discontinued due to the Poček military training ground.
* The mean water levels of the lakes are read from the basic topographic plans at a scale of 1: 5,000 (TTN 5), and the water levels at extremely high waters in November 2000 were measured in the field (Taken from: Kovačič and Habič, 2005: Karst Intermittent Lakes Pivka (SW Slovenia) Acta carsologica, 34, 3: 619–649)
Characteristics of Upper Pivka Basin
Upper Pivka Basin is characterised by transivity, which manifests itself in a variety of ways:
- contact between limestone and flysch rocks,
- hydrographic watershed between the Black and Adriatic sea basins and karst bifurcation (groundwater flow in different directions at different water levels) on this watershed,
- location between the sub-Mediterranean and continental parts of Slovenia.
Upper Pivka Basin is the southern part of the Pivka basin, which was formed on limestones and has some karst characteristics. Upper Pivka’s ‘basin’ is approximately 16 km long and 4-5 km wide. Its surface gradually descends from 620 m above sea level near Koritnice, at the foot of the Snežnik massif in the southeast, to 520 m in the north-western part near Prestranek or Rakitnik, where the river Pivka turns into flysch rocks. Upper Pivka’s surface consists of a flat bottom along the Pivka river and a higher rock terrace along Javorniki massif, into which the hollows of the Pivka intermittent lakes are deepened. This means that the Pivka lakes are on the right bank of the Pivka river, with only Radohovsko jezero Lakes on the left bank (at the foot of hill Primož).
Upper Pivka Basin has a relatively shallow karst groundwater compared to the neighbouring karst hills Snežnik and Javorniki. The underground outflow of karst water in the direction of the Reka river is prevented by the flysch rocks beneath. A watershed connects the Black and Adriatic sea basins at Upper Pivka. The Pivka river is part of the karst Ljubljanica river while the area south of the Pivka springs falls to the Reka river basin. As a result, Šembijsko jezero Lake, the southernmost of the Pivka lakes, flows beneath the surface into the Podstenjšek spring, a right tributary of the Reka river.
Upper Pivka, which is part of the karst Ljubljanica river basin, is located in the water protection area of the Malni pri Planini water source, which supplies water to the municipalities of Postojna and Pivka. Palško jezero lake, the largest of the Pivka lakes, is included in the research along with two caves (Matijeva Jama and Jama v Ždinku) in order to find a reserve water source for Postojna and Pivka that could temporarily replace the catchment in Malni in the event of disruptions. More about this research can be found at:
A search for an alternative water source for Postojna and Pivka
Do you want to learn more about the geomorphological features of Upper Pivka? Read more
Pivka intermittent lakes as a lake family
The intermittent lakes on Upper Pivka Basin are known by various names, including Pivka lakes, intermittent Pivka lakes, and Pivka intermittent lakes. The name Pivka intermittent lakes is gaining popularity since the opening of the Ecomuseum of the Seasonal Lakes of Pivka and the establishment of the Seasonal Lakes of Pivka Nature Park.
The Pivka intermittent lakes are a lake family made up of 17 variously named intermittent lakes that are all located on the Upper Pivka Basin. The intermittent nature distinguishes them from other lake families in Slovenia. In a narrow sense, the “Pivka family” consists of the Pivka lakes, but in a broader sense, it also includes the aquifers Snežnik and Javorniki, from which the waters flow underground towards Upper Pivka, and the river Pivka, with which the Pivka lakes are connected underground, as water from some lakes flows underground into the Pivka’s side springs.
Seventeen picturesque Pivka intermittent lakes entice nature lovers with their mystery and unpredictability. Lakes differ in size, altitude, depth, lake basin formation, frequency of occurrence and duration, and stages of filling and emptying. Most lakes are shallow, with a 1 to 2 m difference between sea level and mean water level, and at extremely high-water levels, the depth of some lakes can increase by several metres (most notably at Šembijsko jezero and Bačko jezero Lake). Palško jezero Lake is the deepest (above 10 m at medium water level and above 20 m at extremely high-water level). In the direction of the Pivka river, the Pivka lakes series begins with the southernmost Šembijsko jezero Lake and ends in the north with the Jeredovce Lake, which is already part of the central training grounds of the Slovenian Army Poček. Interventions in the past have only reduced the size of Kalsko jezero Lake and Radohovsko jezero Lake, out of the 17 lakes.
The following are the unique characteristics of the Pivka intermittent lakes:
- abundance (a group of 17 lakes, which is a unique hydrological system of intermittent lakes in Slovenia);
- small size (small bodies of water, except for the two largest lakes: Petelinjsko jezero and Palško jezero);
- dispersion (the lakes are located at a distance of 15 km between the settlements of Šembije and Žeje pri Prestranku; the largest concentration of lakes is between the settlements of Bač and Parje).
During high-water levels, groundwater from the shallow karst aquifer Upper Pivka Basin spills to the surface, filling the Pivka riverbed and several smaller karst basins, which eventually turn into intermittent lakes. Pivka lakes are divided into nine lakes that appear more frequently and eight lakes that appear less frequently.
In general, lakes that occur less frequently are higher in elevation and farther away from the Pivka river than nearby lakes that occur more frequently.
What are the names of individual Pivka lakes?
What is the significance of Pivka lakes as small water bodies?
Improved links between the implementation of the three water management and nature protection directives (Water Directives, Birds Directive, and Habitats Directive) could be one of the mechanisms to improve the protection of small bodies of water.
Pivka and its surroundings are beautiful to visit at any time of year. Every day, the visitor’s attentive eye can notice different images of nature.
In the spring, when everything blossoms and bursts into life, when the lakes are full, and the landscape is lush green. During the summer, the lakes transform into meadows of colourful flowers with playful butterflies. Autumn offers visitors a spectacular display of colours in the forests, as well as mushrooms and chestnuts, and yes, the lakes are once again a part of it! Even in the dead of winter, skating on an icy lake or simply strolling through peaceful nature is enjoyable.
The intermittent lakes of Pivka are scattered throughout the Pivka basin. At a distance of 15 kilometres by air, we find 17 lakes, which is unique in Europe. We find both large and small lakes. Some are higher in elevation, while others are only filled during heavy rains… The series of Pivka intermittent lakes begins in the north with Jeredovce Lake and ends in the south with Šembijsko jezero Lake.
In comparison to the Pivka river, why and how are the Pivka intermittent lakes formed?
There are several reasons why the Pivka intermittent lakes are turning into lakes and flooding in other areas of Upper Pivka. The primary reason is that more infiltrated rainwater flows into the area underground in a given period of time than the permeable karst soil can transfer through the system of cracks and underground channels, causing water to spill to the surface. Another reason is the low permeability of underground channels leading to karst springs in Planinsko polje. Waters from the Javorniki area flow underground towards Planinsko polje at low water levels, and they also flow towards Upper Pivka at high-water levels.:
What is an intermittent lake?
The Pivka river springs near Zagorje and flows underground into the Postojna Cave. In the Postojna Cave System, the Pivka river has carved out more than 20 kilometres of underground tunnels. The river Pivka today contains much less water than it did during cave formation, and the process of creating the Postojna Cave took at least a million years.
During dry periods, the groundwater level in the upper part of the Pivka riverbed is also 10 metres or more below the riverbed, making it mostly dry. After heavy rainfall, the level rises and karst springs along its supplying stream are activated.
After heavy or prolonged rainfall, the level of karst water begins to rise and, under favourable conditions, reaches the bottom of the Pivka intermittent lakes’ hollows. As the water level rises, groundwater flows to the surface through wide cracks or karst channels at the bottom or slope, forming lakes. As groundwater levels fall, lakes begin to empty, and water is lost in karst canals and cracks.
Karst inflows and outflows as part of the Pivka intermittent lakes’ natural heritage
The understanding of lake basin formation and karst inflows and outflows is the foundation for explaining the dynamics of filling and emptying the Pivka lakes.
What do the terms “karst inflow” and “karst outflow” mean?
Because most Pivka lakes are small, their karst inflows and outflows are smaller, and the riverbeds are shorter or do not exist. It is a diverse group of lakes with varying karst inflows and outflows, and the number of lakes in each lake basin varies. As the largest lakes, Palško jezero and Petelinjsko jezero have the most of them.
Lakes that occur more frequently have sporadic springs, estavelles, sinkholes, or ponor (except Radohovsko jezero Lake). Springs or estavelles are located on the edge of the bottom or slopes of lake basins, from which streams flow to the basin’s lower part. Lakes, which occur less frequently (except for Šembijsko jezero Lake), are filled and emptied solely by the rise and fall of the karst water level through alluvium, with some also filled by dripping from the ground.
When it rains heavily in the autumn and winter, the karst hollows in the Pivka region slowly fill with water from karst springs, which can form right in the middle of the meadow.
When the precipitation stops and the amount of water in the ground does not rise, the water slowly flows underground towards Planinsko polje. In addition, the lakes are gradually emptying, as evidenced by the falling water level. The water flows back into the ground through ponor or the grass itself, and the lake dries up and the water dries up, and during the summer, when there is no heavy rainfall, the lake transforms into a flowering meadow full of butterflies, birds, and other inhabitants.
The dynamics of the occurrence and duration of Pivka intermittent lakes in relation to the Pivka river
When the water level rises, the lake basins (of the Pivka intermittent lakes) fill up with water, and the surface flow of the Pivka river appears, which also floods. We usually look forward to the formation of Pivka lakes (which are natural beauties or natural values that do not endanger settlements), whereas floods can cause considerable damage (we perceive them as natural disasters).
What does the phrase “formation of lakes” of intermittent lakes mean?
The frequency of occurrence and duration of lakes in the Pivka intermittent lakes vary from year to year because they are determined by the amount and distribution of precipitation (precipitation regime) and the saturation of the underground (and soils) with water (previous precipitation and lakes).
Prestranek, located in the middle course of the river Pivka, is the first water metre station. Its surface flow is still intermittent there (on limestone). Surface water monitoring is conducted on the Pivka river near Slovenska vas for the Pivka spring – Prestranek surface water body, which, according to the Slovenian Environment Agency, achieves good chemical and ecological status.
Pivka intermittent lakes are a complex (partly predictable, partly unpredictable) hydrological system with distinct lake dynamics that apply to lakes in both basic hydrological groups (lakes that occur more often and lakes that occur less frequently). The Pivka river shares the most similarities with Petelinjsko jezero lake, and it is also the closest to the Prestranek water metre station. When compared to other lakes, it is notable for its longer existence.
The Pivka basin is a region along the rivers Pivka and Nanoščica that is bounded to the north by high karst plateaus Nanos and Hrušica, to the east by Javorniki, to the west by Slavinski ravnik, and to the south by Snežnik and the valley of the river Reka. The Pivka basin, which includes the Pivka river, is part of the karst Ljubljanica river basin, which merges with the waters flowing from Notranjska (Trbuhovica, Obrh, Stržen, and Rak rivers) in Planina cave.
The northern part of this large basin is made up of impermeable flysch rocks that are subject to surface water runoff. The southern part, Upper Pivka, was formed on limestones and has some karst characteristics.
Pivka gives the basin a name and a unique stamp because this intermittent river carved its bed into the karst plain, which is flooded at high-water levels in the lowest parts, resulting in the formation of intermittent lakes. The basin contains 17 oval hollows, which become temporary lakes as groundwater levels rise in the karst.
The Pivka basin is approximately 25 kilometres long. The Upper Pivka basin is the southern part of the basin, which is about 16 km long and 4-5 km wide. Its surface drops slightly from 620 m above sea level in the southeast near Koritnice, at the foot of the Snežnik massif, to 520 m in the northwest near Prestranek or Rakitnik, where the river Pivka flows into flysch rocks. Pivka is the largest river in the basin. It gets its water from flysch and karst springs in Upper Pivka Basin and sinks in the basin’s north-eastern Postojna Cave.
The basin’s bottom is distinguished by level ground along the Pivka river. Only near the settlement of Pivka is the bottom completely flat; elsewhere, it is slightly undulating and raised a few metres above the bed of the Pivka river; in some places, there are also low cliff peaks. On the west side, the flat bottom gradually rises into slopes, while on the east side, the flat bottom abruptly rises into the steep slopes of the higher terrace, which rises 10–20 m above the basin’s bottom. The rocky bottom is covered in some places by a thin layer of clayey or sandy sediments.
A higher rock terrace on the eastern side of the basin, between the bottom and Javorniki massif, is strongly divided in the northern part. The terrace’s surface is divided by individual mounded peaks and, most notably, numerous sinkholes. Sinkholes are larger along the lower western edge, and there are several large sinkholes and flat-bottomed hollows with the occasional Pivka Lake.
The lake basins’ bottoms are at a height that is still reached by the fluctuation of the karst groundwater level. Water appears in the many karst canals as it rises, and it also appears at the bottom of the valley, where the Pivka springs and flows. The high level of karst groundwater allows water to appear on the surface and the formation of up to 17 lakes.
As a result, the Pivka intermittent lakes are not permanent and only fill up during heavy rains. The water we see as a lake is essentially a surplus of groundwater that the karst world cannot conceal from the living above-ground world.
Sources and references
- Biggs et al., 2014: Report of the Workshop on the Protection and Management of Small Water Bodies. Brussels, 14th November 2013. Brussels, European Environment Bureau, Freshwater Habitats Trust: p. 23
- Hydrogeological characteristics of the area of intermittent Pivka lakes. 2005. Petrič M., Kogovšek J., Acta carsologica
- Kirn, 2016: Nature conservation starting points for the protection of Pivka intermittent lakes: master’s thesis (University of Ljubljana, Biotechnical Faculty): p. 280)
- Kovačič G., 2014: Šembije intermittent lake. Geographic Review, 61, 4: 13–21
- Karst intermittent lakes of Pivka (SW Slovenia) by high waters in November 2000. 2005. Kovačič G., Habič Š., Acta carsologica
- Intermittent lakes in the Pivka region. 2005. Mulec et al., Acta carsologica
- Intermittent lakes of Upper Pivka – protection over time. 2005. Cernatič, Gregorič A., Gorkič M., Acta carsologica
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