Water in Podyjí
The water regime in Podyjí National Park
The natural backbone of the Podyjí NP is the Dyje river, which meanders through the park for 42.5km, even though this section of natural river is sandwiched between the Znojmo and Vranov Dams. The Dyje’s tributaries in this section are short streams with low flow levels, so the chemical, physical and biological properties of the water are determined by the existence of the Vranov Reservoir, which lies upstream of the NP. The water which passes through this reservoir changes its properties, becoming colder and with lower concentrations of dissolved chemical elements and nutrients. The water has also carried lower levels of insoluble materials since the Vranov Dam was built. The peak period electricity which is generated by the Vranov Hydroelectric Plant causes the massive fluctuations in flow levels in the Dyje – from almost no flow at all, to a regular peak of 52m3/sec. This has strongly negative effects on the aquatic ecosystem, and on the formation of abrasive reliefs and also causes erosion of the banks. The river only returns to its natural temperature conditions, with a reduction of daily flow oscillations to a minimum, downstream of the reservoir in Znojmo.
Apart from the Dyje river, the Podyjí NP territory and its buffer zone are very poor in water surfaces. Apart from the Znojmo Reservoir (covering 54ha), which serves as a balancing reservoir for the Vranov Hydroelectric Plant, there are only 21 small fishponds here. The largest of these ponds is the Čížovský Nový Fishpond, with a water surface of 1.8ha. We can also find several pools which cover very small surface areas, but these pools are extremely significant for the development of many amphibian and invertebrate species.
Negative factors which influence the water regime in the NP include the irrigation pumping station at the Devět Mlýnů to action, and the remaining land drainage systems. Potential pollution dangers for the water in the Dyje river arise from the livestock farming operations and the waste water and sewerage run off from the surrounding villages. Unfortunately, the villages of Lukov, Horní Břečkov (including Čížov) and Onšov and part of the small town of Vranov nad Dyjí are still not connected to the mains sewerage system. If such contaminated water were to leak or escape, its path to the Dyje river would be less than 3 km long. The whole NP territory is vulnerable to point pollution, as well as to widespread pollution from arable farming. This is especially due to the fact that all water and potential pollutants flow towards the centre of the territory and then through the whole length of the Dyje river in the park.
Author: Martina Kosová