A Veszprém Megyei Múzeumok Közleményei 7. (Veszprém, 1968)

Sági Károly: A Balaton vízállástendenciái 1863-ig a történeti és kartográfiai adatok tükrében

Water-level Tendencies of Lake Balaton until 1863 Based on Historical and Chartographical Data The Balaton water-gauge at Siófok had been set up in 1863. The water-level of the Lake has shown since that time a fluctuation from +192 cm to — 19 cm referred to the 0 division of the gauge. Since the methods to be discussed below are not suitable to show within short time periods the height of the Balaton water-level above the level of the Adriatic Sea, only tendencies of former water-levels can be discussed. According to the pollin-analytical investigations of B. ZÓLYOMI supported also by the results of recent geological researches, the Balaton was formed after the maximum of the Wurm III. In its ancient state the Lake was larger than it is today. Its greatest extent is shown in fig. 1 (after CHOLNOKY). This extent could be possible only in the case of a water-level higher than the present one. According to the investigations of B. BULLA the upper limit of the Balaton's abrasive activity should be set at the height of 116 m above the level of the Adriatic Sea. Borings into the basin of the Lake have resulted in layers of turf under today's water-surface. By L. LÓCZY, sr. these layers in the Keszthely Bay have been found at altitudes of 97,9 and 100,3 m above the level of the Adriatic Sea. The layers of turf have been observed also by B. ZÓLYOMI who puts the time of formation of the upper layer of turf in the Corylus-Age that would be identical with the Mesolithic. In the Mesolithic (12 000— 5 000 В. C) only the deepest parts of the Lake had an open water-surface that was surrounded by vast marshy areas. On the basis of the height of the archeological levels of settlement observable on the shores and the former islands of the Balaton, ranging from the Neolithic up the accurate maps published in the 18th century a limiting value can be found above which the water-level of the lake could not possibly rise. A shortcoming of this method is that it gives no hint for determining the water-level minimum. The tendency of the water-level in the Neolithic and the sebsequent Copper Age was low, fluctuating around the level-height of our days. In the early Bronze Age the Balaton's water-level must have been lower than it is today while in the following period of the prehistoric age its height was about the same as it is today. In times of the Roman Empire the Balaton's water-level might have been lower than today's level. The Roman historian Aurelius Victor recorded that emperor Galerius built a canal between the Balaton and the Danube River. This alleged Roman canal had already been subject of research several times. B. KUZSINSZKY assumed to have found a Roman sluice at Siófok which according to the results of recent excavations has proved to be a remnant of the Turkish fortification at Siófok. It is likely that Aurelius Victor had been prompted to put down his record by the extensive regulation of water-ways carried out in the Mezőföld (region of Hungary between the Balaton and Danube) as a preliminary state to the construction of a road system. In the period of the great migrations the Balaton had a falling water-level tendency. In the early Arpadien age, on an island at Fonyód-Bélatelep a settlement was possible on a level 103,4 m above the sea-level. The main reason of the population changes at the time of the Hungarian settlement is seen by E. MOOR in the long period of aridity. In the 16th and 17th century the Balaton's water rose considerably having washed away a great part of the ancient earthworks at Balatonföldvár and Balatonboglár and having destroyed one part of the Balatonszemes Castle dating from the times of Turkish occupation. At Balatonszemes the base line of the abrasion slope runs at a height of 108,2 m above the level of the Adriatic Sea. On the offshore bar at Balatonberény at a level of 107,10 m rounded-off fragments from the 16th and 17th century have been found accompanied by the valves of lake-shells (fig. 2). The fragments and shells drifted ashore suggest a water-level higher than 107,10 m above the level of the Adriatic Sea. A high Balaton water-level is suggested also by the name Máriaasszonysziget, in fact a peninsula at Vörs, whose contour map is shown in fig 3. The mediaeval village of Vörs had been settled in the northern part of the peninsula. Since in the case of a water-level 108 m above the Adriatic Sea would scarcely have been left place for the settlement, the water-level in the time of the Turkish occupation could not possibly be higher than 107,5 m. Concerning the Balaton's water-level from the 18th century on we are in the possession of accurate maps prepared by engineers. On the basis of these maps, after having put them on the scale of the known contour-lined maps, the water-level height at the time of preparation of the relative maps above the level of the Adriatic Sea can be calculated. On the basis of a map drawn between 1747 and 1755 (fig. 4) we get a water-level height of 106,4 m above the Adriatic Siea. By using a map made in 1769 (fig. 5) the water-level should be about 105,25 m. By using another map also drawn about 1769 (fig. 7) the calculated water-level is between 105 and 106 m above the level of the Adriatic Sea. L. BENDEFY has made the attempt to express the results of measurements carried out by S. KRIEGER in 1775 in an up-to-date System. According to him the water-level of the Lake in KRIEGER's time was 109,80 m above the Adriatic Sea. Such a high water-level cannot be read from KRIEGER's map the part of which referring to the surroundings of Keszthely is shown in fig. 8. By confronting this map with the contour-lined map of Máriaasszony-sziget at Vörs (fig. 3) we get a 30 465