Where does so much water come from? – A study of the most abundant catchment area in Poland

In Poland, the average water abundance expressed in unit discharge (g) (outflow/catchment area) is ~5.5 ^l/s/km2. High water resources in southern Poland, in mountainous areas (Carpathians, Sudetes), are genetically related to the so-called orographic precipitation. The highest resources are found in the Tatra Mountains and result from the circulation of water in karst systems and its abundant outflow from extremely productive springs, usually called vents.

The most well-known Wywierzysko are: Olczyskie Wywierzysko (Olczyska Valley), Lodowe Źródło (Koscieliska Valley), Chochołowskie Wywierzysko (Chochołowska Valley) and Goryczkowe Wywierzysko, Wywierzyska Bystrej Dolne and Bystrej Górne (Bystrej Valley). All of them have an average outflow of ~100 l/s. Analysis of maps and publications indicates that unit outflow in the Tatras during lows is highly variable and usually spatially related to valleys (Fig. 1).

For example, the specific outflow from the catchment area of the Bystrej stream ranges from 20-25 ^l/s/km2, and there are as many as three wywierzyska: Bystrej Górne and Bystrej Dolne, as well as Goryczkowe Wywierzysko. There are also catchments where the unit outflow, despite the presence of an wywierzyska, is 8-10 ^l/s/km2 (Kościeliska Valley). It is worth noting that in the Tatra Mountains there is a catchment area of Olczyska and the “U Lisów” stream, where the unit outflow during lows is very high (q> 25 ^l/s/km2). The study focused on the catchment area of the “U Lisów” stream, since the thematic maps show a very high outflow, despite the absence of a vent.

The stream “U Lisów” – characteristics

It begs the question: how is it possible to have such abundant water in the absence of a vent?

The catchment area of the “U Lisów” stream is located in the Carpathian Mountains, in the Tatra Mountains, within the Tatra National Park. It extends from the vicinity of the hamlet of Lysa Polana to Palenica Białczańska. The studied catchment area (2.31 ^km2) is mainly composed of carbonate rocks, i.e. limestone and dolomite, where on the northwestern side the rocks extend above the surface (Goły Wierch).

On the southeast side, the sedimentary rocks are covered by Holocene Quaternary formations, which consist of boulders, sands and moraine clays (Figure 2). Due to the geological structure of the area (carbonates and alluvium), water can move between catchments by groundwater drainage.

The higher parts of the basin are located in a northwesterly direction, with the highest peak of the ridge at 1,430 meters above sea level, while the lowest point in the basin is at 950 meters above sea level, at the mouth of the stream to the Białka River (Fig. 3).

The catchment area of the “U Lisów” stream is located in the area of influence of the temperate transitional climate of the high mountain variety in the moderately cool and cool floors. These floors are dominated by air temperatures in the range of 2°C to 4°C and average annual precipitation of 1200 mm to 1400 mm.

Research Methodology

In order to learn about the genesis of waters in the catchment, the area was surveyed using the hydrological-chemical mapping method. The method involves locating water objects (outflows and watercourses) in the catchment and determining physical-chemical parameters, i.e.: water temperature and specific electrolytic conductivity referenced to 25°C [PEW 25°C], which allows field estimation of water mineralization. The higher the conductivity, the higher the mineralization, i.e. the sum of dissolved ions in the water. The above parameters at 128 sites (outflows, watercourses) were measured with a WTW Multi 350i conductivity meter (Fig. 4). Water velocity was measured with an electromagnetic mill at the mouth of the stream to the Białka River, and the flow rate was calculated using the indirect point method.

The chamber work consisted of calculating the hydrographic parameters of the catchment (crenological index and density of watercourses) and analyzing the distribution of physical and chemical features of groundwater and surface water. The catchment parameters concerned the symmetry of the catchment, the analysis was carried out between the left bank side and the right bank side, where the main watercourse is the westernmost one, called the “U Lisów” stream (Fig. 5).

Summary of research results

Measurements of water flow made in winter are particularly important in assessing the abundance of groundwater, since the watercourses are practically fed by it. During the low season, the water flow in the estuary section of the “U Lisow” stream was 81.1 l/s, and the unit outflow – q=38.7 ^l/s/km2. Such a high unit outflow testifies to the high abundance of the catchment area. In comparison, at the same time in Bialka at Lysa Polana, the IMGW site recorded an operational flow (NZQ = 1.49^m3/s), which corresponds to a unit outflow of 23.45 l/s/km2^from a catchment area of 63.54 ^km2. The result testifies to the fact that the resources of the small stream catchment are almost twice as large as those of the Białka River catchment.

The catchment area of the “U Lisów” stream – 2.31 ^km2 – is asymmetrical. On the left bank side it has an area of 1.78 ^km2, and on the right bank – 0.58 ^km2. In the catchment area of the “U Lisów” stream, 32 outflows have been identified, with most of the sources located on the left-bank side, and the threshers on the right-bank side. The number of left-bank outflows is similar to the number of outflows on the right-bank side, however, the crenological index (^outflow/km2) is almost three times lower on the left-bank side than on the right-bank side. The length of all left-bank tributaries (0.5 km) is five times less than that of right-bank tributaries (2.5 km) (Fig. 6). The density of left-bank tributaries is several times less than that of right-bank tributaries.

In the catchment area of the “U Lisow” stream, the physical-chemical characteristics of the waters vary. The average conductivity of groundwater is 124.4 μS/cm, for left-bank waters is higher than right-bank waters (145.4 μS/cm and 96.9 μS/cm, respectively). Groundwater with higher conductivity (158.9 – 247.0 μS/cm) is found in left-bank springs (Figure 7). Groundwater with low conductivity (48.3 – 88.3 μS/cm) mostly represents outflows from the threshers, which are located in the source section of tributary No. 1. The average conductivity of surface water in the basin is 115.0 μS/cm.

Waters with higher conductivity (126.2 – 247.0 μS/cm) are found in the main stream “U Lisów” (Fig. 8). Waters with lower conductivity are found in the right-bank watercourses. Waters with very low conductivity (23.5 – 75.2 μS/cm) are most common in tributary No. 1, starting from the main outflow, as well as in the watercourses of neighboring catchments: the Waksmundzki Brook and the Białka Brook.

Conclusions from research and observations

Based on the study, it was shown that the water resources of the catchment area of the “U Lisów” stream during winter lows are the highest in the Polish Tatra Mountains, and this is not genetically related to the presence of an efficient overhang, but to numerous groundwater outflows and water drainage along smaller watercourses.

The complex geological structure results in groundwater of different genesis. Left-bank springs are associated with the drainage of water in carbonate rocks from the northwestern part of the catchment, while right-bank mudflats are the result of filtering water in river alluvia. This is evidenced by the increased mineralization of the waters in the springs and the decreased mineralization of the waters from the hamlets, as well as the temperature of the waters, which was higher in the left-bank springs.

Highly mineralized waters in the basin are found in the “U Lisów” stream and its left-bank springs (Fig. 9). This is probably due to the long-term circulation of water in the carbonate massif. Water enters through ponors, both in the catchment of the “U Lisów” stream and in the neighboring catchment of Zloty Potok (Area 1). The least mineralized waters in the catchment are found at the beginning of tributary No. 1. The neighboring Waksmundzki Potok has similar low mineralization.

This leads to the assumption that water from Waksmundzki Stream infiltrates through the fluvioglacial cone into the catchment area of the “U Lisów” stream (Area 2). Low-mineralized water is also found in the initial section of tributary No. 2 and similarly mineralized water is found in Białka. Hence the suggestion that water from the Białka stream infiltrates from alluvial formations into the catchment area of the “U Lisów” stream (Area 3).

Based on this, it is possible to identify the three most important alluvial areas of water, which supply water to this small catchment, resulting in a catchment with the highest hydration in Poland (expressed in unit outflow).