Hidrológiai Közlöny 1949 (29. évfolyam)

11-12. szám - Értekezések. - J. SÜMEGHY, D. Sc.: Artesian wells of the Hungarian Plains

The seconcl group is of less importance. Sediments filling them up do not always eover the whole surface of the basiu but extend only over the area of somé synelinals and therefore they are only of local importance as waterbearing strata. Only the generally 1500 m. thick Pannonian strata extend over the entire surface of the basins, but their loAver half is impermeable. Therefore only the upper half— consisting mostly of sands and other loose sandy sediments — is of importance. Its water is under hydrostatic pressurc already. Most artesian springs are supplied with water of these strata. Influx of water to this zone is assured by the great Karst-water bearing ranges too, which contact the loose upper Pannonian strata along large surfaces. The bottom water levei of the two water-bearing svstems is about the sarne, in the depth of about 1000 m. This depth is generally the deopest limit of artesian wells, because deeper drillings are supplied mostly by ascending juvenile hot waters. But in the Hungárián hasin svstem, there are plaees where thé origin of the artesian water can be explained alsó by the classical theory. These are the above inentioned cauldrou-like depressions, filled up with UpperPliocene and Pleistocene sediments. There are places as well, where the wells receive their water from higher-lying catchment areas and thus the ascension of water can be explained here bv the theory of communicating vessels. Pleistocene depressions in the Pannonian strata can be found in the midst and on the southern bordér of the Alföld, above the DravaSava sunk-land, in the West-Hungarian and Transylvanian basins. Their sediments are usually of coarse sandy cbaracter. Their generál depth is several hundred meters. but in deep rift-valleys and eauldrons they are sometimes even 1000 m. t.hick. Tliese depressions are rich in water, because usually more fans of detrital matter filled them up and the surrounding strata are diiiping mostly concentrically towards their bolton. Thus their catchment areas are large. Generallv speaking the basins of our hasin system are filled up mainly of maris, clays and similar sediments. witliin which several secondary Pliocene and Pleistocene depressions can be found, with loose, sandy sediments. These are the richest storage rocks of artesian water. Although the main water-containers arc independent geological units, they may com municate with one another through the faultecí and fractured structure of tne hasin system. The theory that the cliemical components solved by water are a petrologic feature of the containiníí formation is therefore of hypotlieti ca.l value.

4 The mostly alkaline, AV/CZ-containing artesian Avaters of the central basins contain more 4 Szádeczky—Kardoss, B.: A nagyalíöldi urtézivizek főtípusai és azok szintjelző értéke. — Bányászati ös Kohászati Lapok. LXXV. vol. no. 16. p. 305—308. Budapest. 1941. agressive CO• and Fe than usual. Exeptions are the waters of the depression near Győr and the waters of the Holocene depression of the Körösköz, which contain many organic impurities. The dissolved salt contents of the waters of the Upper-Pannonian are smaller than that of the Lower-Pannonian and at the base, the salt contents opproaches that of the oil-fieldsalt-waters.

5 The yield of the wells depends on the geological structure. Wells supplied by the Pannonian strata are poor producers and of short duration. Their water yield is about 50— 100 ltr./sec. The wells of the Levantian-Pleistocen depressions — on the other hand — are rich producers and of long, duration. The richest wells are that of the Tisza—Maros corner. The 280 wells of tbe town of Szeged — for instance — give 77,000 ltr. water/sec.. the 650 wells give 1000 Itr./sec. The totál yield of all wells of the Hungárián hasin system is about 1,000,000 ltr. water/sec. Their femperature is generally high. That of the 150—200 m deep wells is about 18— 20 C°, of tihe 300—350 m, deep ones is 25—26 C°. The r-aase of this is, that the geothermical gradient of the hasin sediments is lower. (18— 20 m.) than usual." Aeeording tho Horusitzky the oondensation of water-vapours is a sufficient heat-source for this „heating" of the basin sediments. Ascension of these vapours is effected up the faults and fractures of the base rock.

3 Aeeording to their depth the wells can be devided into three groups. Those of the first group have depth of 25—100 m. Their number because of wasteful operatiou, most of them through wasteful operation, most of them became negatíve. They received their water mostly front delta cones and slopes of detritus near to the surface. The second group is that of the PleistoceneLevantian secondary basins, with an average depth of 150—200 m. They are rich in water and their number is large. To the third group belong wells of 300— 450 m. average depth; they obtain their water usually from the Upper-Pannonian strata. They are too numerous and overexploitation of the water-bearing strata has resulted in the deerease of hidrostatic pressure and of the water yield. These wells are of shortest duration. There are springs of 500—600 m. but their number is small in proportion to the re'st. During the last 20 years many bores have been drilled to 1000—2000 m. depth and more for petróleum, salt and thermal water exploration. They have surfaced no more artesian wa

+ier, but ascending juvenile thermal water of 147 C° near the base. 5 Szurovy, G.

: A nagyalföldi úíabb mélyfúrások hidrológiai eredményei. — Hidrológiai Közlöny. 1947. 1—4. sz. Budapest. 1947. c Siimeghy, J.: l)ie geothermischen Gradienten des Alföld. — A Magy. Földtani Intézet Éivkiinyve. XXVIII. vol. p. 275—370. Budaipest, 1929. .353