Geologicka rizika pri planovane stavbe vodniho dila Skalicka pobliz Hranickeho krasu a Hranicke propasti

The basin of the Bečva River is among those areas in the Czech Republic that are most exposed to floods danger. The disastrous flood in July 1997 had a devastating impact on settlements in the basin and the zone along the Morava River also draining the catchment, thus becoming an impetus to seeking for best protection against floods. This also restored the plan from the first half of the 20^th century to construct water management works in the vicinity of the spa at Teplice nad Bečvou and the municipality of Skalička. Currently, the works of medium size are proposed within the river stretch upstream of Skalička with a maximum water level of 265.00 m ASL, and the total volume of 42.1 million cubic meters. The planned dam of the reservoir is located roughly three kilometres in beeline from the Hranice Karst - more specifically, from the Hranice Abyss.
The Hranice Karst of hypogenic origin is extending on the eastern tip of the Maleník fault block and forms part, along with the entire fault block of the Paleozoic sedimentary cover, of Brunovistulicum. On this basement there is a sequence of sedimentary rocks of Middle Devonian (Eifelian) up to Carboniferous ages (Mississippian/Viséan). The karst alone has developed in Devonian carbonates of Givetian to Tournaisian stages which are included in the Macocha and Líšeň groups of strata. The total thickness of limestones has not yet been established in this area and their basement was never reached by drilling. The thickness of the sequence of carbonate sediments can be assumed only indirectly based on the data obtained by drilling in the larger area (e.g. the Potštát-1 borehole confirmed the presence of carbonates at a depth of 4,200 m; the Choryně-9 borehole revealed the presence of carbonates at a depth of 1,462 m, reaching the underlying paragneiss; the Branky borehole reached paragneiss at a depth of 2,546 m under Devonian carbonates; and the Valašské Meziříčí borehole penetrated a crystalline complex at a depth of 1,462 m under Devonian carbonates.
During the 1997 flood the level of the Bečva River increased by 6 m in the Hranice Karst, while there was increase in the level of mineral water in the karst cavities and an eruptive outflow of mineral water from an unused borehole occurred. This was due to the flood water exhibiting exceptional hydrostatic pressure on groundwater in infiltration area of mineral water. In the long-term, one of such infiltration areas of mineral water has been placed in the bed of the River Bečva near the municipality of Kamenec - directly within the area of designed works (Fig. 1). Subsequently, the continuously increased hydrostatic pressure on this infiltration area is likely to cause an increase in the level of mineral water in both the Hranice Karst and the spa resort of Teplice nad Bečvou. The strongly karstified limestones found in the bottom of the reservoir can also cause considerable problems in terms of engineering geology. Probes are installed at specified karst sites and wells of mineral water to measure the water level, temperature and electrical conductivity of water (Fig. 2). As a result, increased levels of mineral water are consistently observed in both karst cavities and wells with every flood wave. Since there is an increase in the level of mineral water in the monitored objects, with the mineral water being never diluted, the increase occurs due to the influence of increased hydrostatic pressure of surface water.
A polder can be considered as a satisfactory means to control flood and protect mineral water. While the mineral water regime will still be affected in flood events with this method of control, it will be only a temporary situation; after a certain time, the regime will restore its initial status, depending on the specific situation, similarly as with the extreme flood in 1997.

References

Čížek, P. -Tomek, C. (1991): Large-Scale Thin-Skinned Tectonics in the Eastern Boundary of the Bohemian Massif. - Tectonics, 10, 273-286.View article

Dvořák, J. - Friáková, O. (1978): Stratigraphy of the Palaeozoic near Hranice na Morave. - Výzk. Práce Ústř. Úst. Geol., 18, 1-50.

Geršl, M. (2016): Rozlišení vod Hranického krasu na základě archivních analýz. - Zpr. geol. Výzk. v Roce 2015 49, 247-252.

Kalvoda, J. - Bábek, O. - Fatka, O. - Leichmann, J. - Melichar, R. - Nehyba, S. - Špaček, P. (2008): Brunovistulian terrane (Bohemian Massif, Central Europe) from late Proterozoic to late Paleozoic: a review. - Int. J. Earth. Sci. 97, 497-518.

Rožnovský, J. - Středa, T. - Litschmann, T. - Pokladníková, H. - Fukalová, P. (2010): Mesoclimate as a part of recreation potential of the landscape on the example of the Moravian Karst. In: Recreation and Environmental Protection, 60-64. - Mendel Univ. in Brno.

Schulmann, K. - Gayer, R. (2000): A model for a continental accretionary wedge developed by oblique collision: the NE Bohemian Massif. - J. Geol. Soc. London 157, 401-416.View article

Středová, H. - Knotek, J. - Středa, T. (2015): Microclimate monitoring for evaluation of management effect on Mohelno Serpentine Steppe. In: Public recreation and landscape protection - with man hand in hand!, 157-160. - Mendel Univ. in Brno.

Špaček, P. - Bábek, O. - Štěpančíková, P. - Švancara, J. - Pazdírková, J. - Sedláček, J. (2015): The Nysa-Morava Zone: an active tectonic domain with Late Cenozoic sedimentary grabens in the Western Carpathians’ foreland (NE Bohemian Massif). - Int. J. Earth Sci. (Geol. Rdsch.) 104, 963-990.

Ulrych, J. - Ackerman, L. - Balogh, K. - Hegner, E. - Jelínek, E. - Pécskay, Z. - Přichystal, A. - Upton, B. G. J. - Zimák, J. - Foltýnová, R. (2013): Plio-Pleistocene basanitic and melilititic series of the Bohemian Massif: K-Ar ages, major/trace element and Sr-Nd isotopic data. - Chem. d. Erde 73, 429-450. View article

Vrba, J. (1960): Hydrogeologické posouzení území mezi Teplicemi nad Bečvou, Černotínem a dvorem Kamenec, se zřetelem na výstavbu přehrady na řece Bečvě. Závěrečná zpráva. - MS Vodní zdroje. Praha.