CHARACTERISTICS OF WATER FROM SPRINGS IN THE LIMESTONE REGION OF CROATIA Mi1ivo.j PETRIK SUMMARY Data are presented on ,about 100 springs distributed throughout the region. They cover the position and altitude of springs and the following characteristics of their water: temperature, dissolved oxygen, free carbon dioxide, total, carbonate and non- carbonate hardness, alkalinity, calcium, magnesium and chloride. The data were obtai- ned in single or repeated observations, and in case of more important springs in all seasons. The results are grouped for smaller sub-regions and an attempt is made to arrive at general sub-regionalcharacteristics as well as at general characteristics for the entire region. Finally, a comparison is made between the underground water of that region and such water from small-grained water-bearing strata in the non-karsti- fied portion of Croatia. RESUME Caractéristiques de l’eau des sources de lu région calcaire de Croatie Cette étude donne des indications sur une centaine réparties de sources dans toute la régionconsidérée,notamment sur l’emplacementet l’altitude des sources,ainsi que sur les caractéristiques suivantes de l’eau :température, quantité d’oxygène dissous, quantité totale de gaz carbonique libre, dureté en carbonates et non carbonates, alcalinité, cal- cium,magnésium et chlorure. Les données ont été obtenues à la suite d’observations uniques ou répétées en toutes saisons dans le cas des sources les plus importantes. Les résultats sont groupés par sous-région;l’auteur s’efforce de dégager les caractéristiques générales de ces sous-régions,ainsi que celles de l’ensemble de la région. L’étude se ter- mine par une comparaison entre les eaux souterraines de cette région et celles des cou- ches aquifères granuleuses de la partie non karstique de la Croatie. 1. INTRODUCTION From the analytjcal material collected on waters in the limestone region of Croatia, data from 200 points have been selected for the present attempt to arrive at a general picture of the character ofwaters in that region. They cover roughly the drainage areas ofthe rivers Lika, Gacka and Kupa with their tributaries, the region of Rijeka with the UEka mountain,the basin of Plomin in Istria with some additional Istrian springs, the main springs on the Adriatic coast between Rijeka and OmiS,the valleys of the lower Neretva and of the Cetina river, the “polje” of Imotski and the river system Suvaja- Vrlika-Tihaljina-Trebiiat,the region of the Baeina lakes and the islands of Krk and Rab. The selected points represent only a small number of springs and rivers in that region,but, in a general way, include the more important ones of the perennial sources. Their geographical distribution is shown on figure 1 to 4.Their elevation ranged from zero to more than 1,000m above sea-level.Greater springs are, with a few exceptions, between the sea level and 350 m above it. The material was collected by the Institute of Sanitary Engineering of the Faculty of Civil Engineering at Zagreb for 177 points. Supplementary data for some of these points, and data for the 23 additional points were obtained from the public health labo- ratories at Rijeka and Split. A total number of 576 analyses has been used. Their numbers on individual points varied between 37 and one. On points with a larger number of analyses, examinations were made in all seasons, on those with one to four analyses, they were carried out mostly in the period from June to October,in the months, in which they are the least distorted by rains. 624 oc mE vw. - CLUSIAN WPE cr SIWIOIOLE -A- POINT OW TUE RIVER ro e .p 8 BO)(ANJAc NOVlGRP Fig. 1 Of the 576 analyses, 400 contained data on temperature, oxygen dissolved, free car- bon dioxide, total, carbonate and bicarbonate alkalinity, total, carbonate, non-carbo- nate, calcium and magnesium hardness, and chloride. Further 38 examinations lacked either data on carbon dioxide or chloride. The remaining 138 examinations gave infor- mation mostly on temperature, total alkalinity and total hardness, but often also on some other characteristics. gzt 0 RSK I .O0 WOTAR Fig. 2 All determinations were carried out, and their results expressed, according to the best known standards 2). The saturation with oxygen was calculated on basis of Truesdale, Downing and Lowden's table (3), without correction for altitude. 626 2. AREA Geological information was obtained from the newer literature.The limestone region of Croatia was built, with few exceptions of a more local character, in the mesozoic and tertiary age. Smaller palaeozoic regions occur in Gorski Kotar, which makes the highest portion of the upper Kupa and upper Dobra drainage areas, and in the Velebit range where it forms parts of the drainage areas of the Lika river and of some of its left tributaries (4,5v 6$7,R,9), and also around the upper Korana river. They are the least per- meable to water and often form impermeable barries. Ofthe mesozoic, trias covers the least part; lower triassic makes small parts of the region of the main springs of the Lika, Fig. 3 while upper triassic contributes to the region of some other springs of Lika’s tributaries. Jurassic strata also occur in the Velebit, but also in the mountain of Velika Kapela where they include part of the drainage area of the upper Dobra river. The greater part of the mesozoic consists, however, of cretaceous sediments. Lower cretaceous makes the mountain Svilaja and the south-easternpart of the Dinara range, but is also found in other regions, as in the mountain of Mala Kapela and around the lakes of Plitvice (10,11*12;. Upper cretaceous covers the greatest part of the area; it makes the southern and eastern part of Istria, the main parts of the islands,part of the drainage area of the Plitvice lakes, the greatest part of the geographic drainage areas of the rivers Korana, MreZnica and Dobra (below Ogulin), the anticlines of Northern Dalmatia,the region between Sibenik and Split, the greater part of the Dinara, Mosor and Biokovo moun- 627 tains, and of Hercegovina. Next in importance to the upper cretaceous are deposits of eocene which often include strata impermeable to water or suitable for agriculture. Such strata make the northern part of Istria and the north-eastern part of Northern Dalmatia.Long belts of eocene, in single or multiple arrangement, run along the coast from Rijeka to Montenegro. Quaternary strata form some of the large basins, as the “polje” of Sinj and that of Imotski, or the valley of the lower Neretva river. Fig. 4 Both limestone and dolomite appear in all periods. In the palaeozoic, dolomite is found in a restricted measure but is developed in all facies of the mesozoic. Both are subject to corrosive and erosive processes and may be either permeable or impermeable to water, in dependence of the intensity of these two destructive processes in fissured rocks. Dolomite cannot be considered as always impermeable but only as less permeable than limestone. In the region of the lakes of Flitvice, for example, triassic and lower Jurassic dolomite forms the impermeable barrier which is concordantly covered by cretaceous dolomite, corroded and eroded, permeable, and without springs. Subsurface corrosion and erosion can thus develop both in limestone and dolomite. With both, the precondition are tectonic disturbances of sufficient violence to create fissures, especially faults,and in first line crossings of faults. The greatest measure of subsurface corrosion and erosion show the widespread and deep areas of upper-creataceouslimestone which also make the largest part of our region. The drainage areas of the rivers Kupa, Dobra, Mreinica and Korana are wooded in their upper parts, and so is the hinterland of Rijeka, the UEka and the Mala and Velika Kapela, also the continental side of the Velebit. The rest of the region does not contain forests of importance but is, at the best, covered by macchia. 628 3. ANALYTICALRESULTS Limited space prevented presenting of analytical results even in regional groups and much more so individually.With few exceptions,the number of examinations at single points was too small to allow statistical methods. For this reason, it seemed best to present analytical results by the extreme values observed. Repeated examinations on the same points disclosed the general fact that the results varied with time,seasons and weather conditions,in some cases within relatively narrow limits, in other cases quite widely. 3.1 Temperature The temperature of water varied between 4.8 and 18.0"C. It varied inversely with altitude, but springs at the same elevation and in the same region showed sometimes very different temperatures. Thus, the nearly-coastal spring Zvir (point 84), at an ele- vation of 5 m,showed temperatures between 8.4 and 9.1 "C,whilst the coastal spring at Plomin (point 119), at an elevation of 0.5 m., displayed temperatures between 13.3 and 13.9"C;both are in the bay of Rijeka. The low temperatures of the first-called spring are due to the elevation of its drainage area, which is above 300 m,whilst that of the second-calledlies at about 20 m.Coastal springs showed temperatures between 7.8 and 18.O0C,springs between 300 and 350 m above sea-level between 6.6 and ll.O"C, those between 550 and 600 m between 7.2 and 10.2"C.Individual springs,if strong and reliable, showed throughout the year variations of less than 1.0"C. 3.2 Dissolved oxygen The saturation of water with oxygen was generally high, between 54 and llO%, with concentrations between 6.3 and 12 mgil; the usual concentrations were between 8 and 11 mg/l,and the usual saturation between 80 and 100%.