Mountain Hydrology Workshop, Bucharest, Romania, 26 September 2003 CENTRAL EUROPEAN HIGHLANDS AND THEIR HYDROLOGICAL ROLE, WITH SPECIAL REGARD TO THE BOHEMO-MORAVIAN HIGHLAND F. Doležal, T. Kvítek, M. Soukup, Z. Kulhavý, M. Tippl Research Institute for Soil and Water Conservation, Žabovřeská 250, 156 27 Praha 5 – Zbraslav, Czech Republic, [email protected] Central Europe in broader sense comprises high mountains of the Alpine and the Carpathian systems as well as mountainous ranges of medium elevation (between about 1000 and 2000 m a.s.l.), e.g. those belonging to the Bohemian massive, still prevailingly of mountainous character. Both types of mountains act as ”water towers”. Their high elevation brings about high precipitation and low evapotranspiration, and the resulting surplus of water balance feeds large European rivers and other important water sources. Beside the mountains, large areas of Central Europe are occupied by highlands or peneplains of lower altitude (say, between 400 and 800 m) in which the surplus of annual water balance is less noticeable, and of lowlands with passive water balance. This paper discusses the hydrological role of highlands and peneplains, paying special regard to the Bohemo-Moravian Highland (Českomoravská vrchovina, denoted below as BMH), in which several small experimental catchments of the authors’ institute are located. The pattern of long-term average annual water balance of Central European highlands and peneplains (for brevity, the term “highlands” is used below to denote both) varies, of course, from location to location. On average, the balance is positive and provides an average annual surplus of about 100 to 300 mm. This makes it possible for these highlands to feed minor rivers. In this way, BMH gives origin to the Chrudimka, Sázava, Želivka, Jihlava, Svratka and Svitava rivers, beside many other smaller streams. The runoff regime of streams and the turnover of groundwater in the highlands mainly depends on the local geology. Impervious igneous and metamorphic rocks. usually referred to as “crystalline”, of which the bulk of BMH is composed, give rise to the rapid turnover of groundwater in shallow regolith aquifers and to the dense network of temporary springs and minute perennial streams and fishponds. The portion of interflow in the total runoff volume is high (typically about 40 %). The residence time of water in catchments is small (of the order of few months) and is further reduced due to the existence of frequent artificial subdrainage (tile drainage) systems on agricultural lands. Hydrology of these landscapes can be described in terms of three zones (the recharge, the transitional and the discharge zones or, in local terminology, the infiltration, the transport and the accumulation zones). Water supply sources are small and dispersed (except for few recently built reservoirs on larger rivers). In terms of water quality, the rapid turnover of water does not allow enough denitrification to occur and most regions of this type are highly vulnerable to water pollution by nitrate. The catchments on precambrian metamorphic rocks in South-West Bohemia behave similarly in broad terms but their water residence time is slightly longer, about a half-a-year. This is indicated by summer maxima of nitrate concentration in small streams and subdrainage water, in contrast to early spring maxima observed in the region of “crystalline” rocks. The hydrographic network in the precambian region is slightly less dense, valleys are broader and flatter. Wetlands and subdrained areas are less numerous and larger. Quite specific is the behaviour of catchments in the North-East Bohemian cretaceous sandstone zone, where small Mountain Hydrology Workshop, Bucharest, Romania, 26 September 2003 streams are temporary, groundwater turnover is deep and water residence times are very long. If the permeable cretaceous rocks are overlain by aeolic (mainly loessial) quaternary deposits, a separate shallow water cycle may develop in them, characterised by rapid groundwater turnover and high proportions of both direct runoff and interflow in the stream flow.