Drinking Water

ZOBODAT - www.zobodat.at Zoologisch-Botanische Datenbank/Zoological-Botanical Database Digitale Literatur/Digital Literature Zeitschrift/Journal: Austrian Journal of Earth Sciences Jahr/Year: 1999 Band/Volume: 92 Autor(en)/Author(s): Schubert Gerhard Artikel/Article: Water Resources - Drinking Water. 295-311 © Österreichische Geologische Gesellschaft/Austria; download unter www.geol-ges.at/ und www.biologiezentrum.at Mitt. Osterr. Geol. Ges. ISSN 0251-7493 92(1999) 295-311 Wien, Juli 2000 Water Resources - Drinking Water GERHARD SCHUBERT1 15 Figures, 1 Table Abstract In Austria, geologists play an important role in exploring and protecting groundwater resources. Concerning the development of investigation methods, Austrian hydrogeologists did pioneering work mostly in the field of tracer techniques. This is demonstrated by some representative examples. Four examples concern the Northern Calcareous Alps, which bear enormous karst groundwater resourc es. These are the Mühlau springs (water supply of the state capital Innsbruck), the Dachstein massif, the Rax-Schneeberg region (First Vienna Water Line) and the Hochschwab region (Second Vienna Water Line). One example concerns the largest pore groundwater aquifer of Austria, the so-called Mitterndorf depression. Here enormous problems with groundwater contamination are present. Introduction to the north of Innsbruck, the Dachstein range in the center of Austria, and the First and Second Vienna Water Lines in Due to the high precipitation in Alpine regions, Austria is a the Rax-Schneeberg and Hochschwab region respectively. water rich country. In higher locations the precipitation The vast pore aquifer of the Mitterndorf depression is situat amounts to about 2000 mm/a (BAUMGARTNER et al., 1983). ed within the southern Vienna basin. The following chapters 3 Although Austria covers an area only of about 84.000 km , should bring some representative contributions of hydroge 3 it produces an average outflow of 55 billion m /a ologists to groundwater exploration and protection in Aus (BUNDESMINISTERIUM FÜR LAND- UND FORSTWIRTSCHAFT, tria. The pioneering work on the field of tracer techniques in www.bmlf.gv.at). This corresponds to an average chatch- the Dachstein region is outstanding. ment yield factor of about 21 Is-1 km-2. In Austria, high productive groundwater resources are located within the carbonate rich units of the Alps, in partic ular within the Northern Calcareous Alps and within expan Mühlau springs sive Quaternary gravel-bodies of valleys and depressions (Fig. 1). The landscape of the calcareous Alpine regions is The Mühlau springs are the prime source of water for the characterized by the occurrence of extensive and frequently state capital Innsbruck. They represent one of the big spring strongly karstified mountain ranges which form productive groups which discharge the Karwendel range, a 40 km long karst aquifers. These karst aquifers contribute a considera and 20 km wide carbonate massif to the north of Innsbruck ble part to the drinking water supply of Austria, e. g. for the (Fig. 1). In the Karwendel range, the most important water cities of Vienna, Innsbruck and Salzburg. Particularly exten bearing formation is the Wetterstein Limestone (Ladinian sive Quaternary pore aquifers are located along the valleys to Early Carnian). This is due to the wide lateral extent, of the Danube, Mur, and Inn, as well as in the Vienna basin. thickness (in the central Karwendel its thickness reaches For example, the state capitals Linz and Graz receive their 3000 m; Fig. 2), and high storage capacity caused by drinking water for the most part from such aquifers. Due to intensive fracturing., In the Karwendel range, according to dense settlement and industry on the one hand, and agri HEISSEL (1993), karst is, as a rule, just slightly developed. culture on the other, these Quaternary pore aquifers are The waterworks of Mühlau have been in operation already exposed to a high risk of contamination. In general, within since 1890. In 1953 new galleries were completed which Tertiary sediments of the Molasse zone and the intra-alpine capture the water deeply in the mountain. They consist of basins, as well as within the geological units of the Bohemi three infiltration galleries (Wurmbach, Klammbach, and an Massif, Rhenodanubian Flysch Zone, Graywacke Zone Rum galleries) and one collector gallery (Fig. 3). The overall and Central Zone of the Eastern Alps only local aquifers with length of these galleries amounts 1663 m. The actual total limited productivity occur. discharge of the captured Mühlau springs varies between The following chapters discuss some important ground- 500 and 2000 l/s, in the course of which this amount is and springwater occurrences in Austria (Fig.1). Within the distributed to the mentioned infiltration galleries in the ratio Northern Calcareous Alps these include the Mühlau springs of 1 to 2 to 7. That means that the major part of the dis- Address of the author 1 Geological Survey of Austria, Rasumofskygasse 23, A-1031 Vienna, Austria. E-mail: [email protected] © Österreichische Geologische Gesellschaft/Austria; download unter www.geol-ges.at/ und www.biologiezentrum.at ro CO CD Hydrogeological Units Quaternary sediments of valleys and basins Regions with good hydrogeological preconditions (mainly gravel and sands) • of abundant ground-water occurrences Tertiary (Oligocene-Neogene) basins BKOTsj Headwaters with 50 100 km (mainly clays and sands) fi&SSS important discharge Rhenodanubian Flysch Zone (sandstone and shale) |(3 1 Regions with artesian wells Extensive occurrences of II i I II Regions described in carbonate rocks within Flysch Zone II I Ml the following chapters: Upper Austroalpine cover, e.g. Northern 1 Karwendel range Calcareous Alps (mainly limestone and dolomites) (Mühlau springs) 2 Dachstein massif Mesozoic limestone, dolomites, 3 Rax-Schneeberg region and slates of Central Zone 1" Vienna Water Line) ^.-> 4 Hochschwab region j * [J Paleozoic slates and phyllites (2"d Vienna Water Line) ftf" 5 Mitterndorfdepression $Qpf^\fv Paleozoic limestone and dolomites p3—I Metamorphic successions of Central Zone I—=J (mainly granits and schist) I—<—i Crystalline of Bohemian Massif '* *' (mainly Variscian granites and schist tvia-JVeus/ed/er See © GO O Fig. 1 Hydrogeological units of Austria (GATTINGER, 1980). © Österreichische Geologische Gesellschaft/Austria; download unter www.geol-ges.at/ und www.biologiezentrum.at Water Resources - Drinking Water 297 charge infiltrates into the Rum gallery which is the longest one (HEISSEL, 1993). In 1989, HEISSEL (1993) remapped the geological situation of the galleries. The result of these investigations is shown in Figs. 3 and 4: The Mühlau springs rise near the bottom of the Inntal nappe. The aquiclude is built by low permeable ba sal strata of Inntal nappe and the upper most part of Thaur unit (according to HEISSEL, 1993, the Thaur unit is a part of the Karwendel imbricate zone; Fig. 2) and by the fault gouge zone in between these tectonic units. Within the Inntal nappe, the sealing strata are Alpine Bunter (an alternation of Skythian sand stone and shale) and the Reichenhall Formation (a heterogeneous sequence £r of carbonates, shale and rauhwacke; Early Anisian). Within the Thaur unit, the aquiclude consists of RaibI Formation (an alternation of carbonates and shale of Carnian age). In the galleries, the infiltration hap pens chiefly within the Alpine Muschel kalk, a heterogeneous Anisian lime stone formation. Together with the over lying thick Wetterstein Limestone (Ladinian to Early Carnian), these car bonates build the Aquifer of Mühlau springs (Fig. 4). The waters of the Wurmbach and Klammbach galleries must have been in intensive contact with the RaibI Formation of the Thaur unit (Carnian), as indicated by a distinct 2 concentration of S04 ~. In the recharge area of Mühlau springs, this Formation contains gypsum (HEISSEL, 1993). From a geological point of view, HEISSEL (1993) suggested that the catchment area of the Mühlau springs amounts 25 km2. To the north he restricted the intake area by the deep syncline in the north of Hoher Gleirsch which includes the sealing RaibI Formation of the Inntal nappe (Fig. 2). In the years 1989 and 1990, Mühlau springs were subjected to an intense hydrochemical and isotope hydrological monitoring program (RAMSPACHER et al., 1992). The aim of this investigations was to determine the intake area and the mean residence time of the outflow of Mühlau springs, as well as to esti mate the total storage volume from a hydrological point of view. From water balance considerations, RAMSPACHER et al. (1992) concluded that the discharge of Mühlau springs corresponds to a re charge area of about 30 to 36 km2. This CO o <u is based on the assumption of a mean O) CM 2 outflow of 1370 l/s. Corresponding to LL. X RAMSPACHER et al. (1992), the hydrologi- © Österreichische Geologische Gesellschaft/Austria; download unter www.geol-ges.at/ und www.biologiezentrum.at 298 G. SCHUBFRT cal data indicate a re charge area reaching further northward than deduced by HEISSEL (1993). The phenomenon that the recharge area esti mated by water balance is larger than that based on geology, occurs also in other regions of the Northern Calcareous Alps. There are two pos sible reasons for this ef fect: The first results from the difficulties in measuring representa tive precipitation heights in Alpine regions. The second is the fact that geological barriers are not completely tight. According to RAMS PACHER et al. (1992), from the relatively low <3180-fluctuations (Fig. 5), i. e. the damping of the input signal, which is giv en by precipitation, the mean residence time of Mühlau springs amounts more than 6 years. By RUM GALLERY way of the exponential model, the Tritium-con tents show that the wa ters from the Wurmbach and Klammbach galler ies (8 to 10 years) are younger than those of 0 m 100 m 200 m the Rum gallery (11 to 15 years). The Rum gal Fig. 3 lery captures a some Geological sketch of the environment of Mühlau springs (HEISSEL, 1993).

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