Kokořínsko Protected Landscape Area

Hydrology

The PLA territory belongs to the three main water catchments (Labe, Jizera and Ploučnice) and six smaller catchments (Pšovka, Liběchovka, Obrtka, Strenický potok, Košátecký potok and Úštěcký potok streams). From a nature protection viewpoint the most significant are the unregulated Liběchovka and Pšovka water courses and some of their tributaries. A well-developed network of wetlands can be found in these areas, which have formed as a result of numerous issues of underground water on the valley floors, natural overflows from the streams and the absence of agricultural usage of these valley floors. As well as the extensive riverine wetlands, several reservoirs and fishponds have been built on the Pšovka stream and several pools (e.g. Kačírek) are of natural origin. Outside of the alluvial plains a number of “heavenly pools” have formed in areas of impermeable bedrock.

Kokořínsko PLA is a part of the Bohemian Cretaceous Basin, which provides very good conditions for the accumulation of ground water, due to its geological structure. The basic hydrogeological features are determined by the character of the Middle Turonian sandy sediments, which make up most of the Polomené hory district. These sedimentary rocks are highly permeable, and there are examples on the PLA territory where permanent streams (or torrential rainfall) are absorbed into the ground before it reaches the larger rivers. In places the water flows into open fissures and cracks. Large quantities of water disappear into the ground in this way in the central reaches of the Pšovka stream. The water which penetrates underground then collects on the impermeable Lower Turonian clayey marlstone (III. belt). This layer is also the roof for water trapped under an artesian tension in the sandstone layers I. and II. of Cenomanian age. The water aquifers in the upper III. belt have been proven to communicate with each other, exchanging water between different stream catchments. For example, water flows between the Pšovka and Liběchovka catchments, from the Obrtka and Bobří potok streams to the Liběchovka and water from the Pšovka catchment has found its way into the Strenický potok catchment.

In the cretaceous layers under the Liběchovka valley both underground water horizons have developed. The upper aquifer is in the Middle Turonian sandstones and has a lower surface tension. The lower horizon has a greater (artesian) surface tension and lies above the base of Cenomanian sediments in the lowest layer of the Lower Turonian. In the Pšovka catchment there is also a strong aquifer present in the upper part of the Middle Turonian layers, which is fed horizontally and vertically and drains into the Quaternary sediments of the Pšovka valley where hidden issues form a secondary concentration of underground water.