Virág Árpád: A Sió és a Balaton közös története. 1055–2005 (KÖZDOK Kft., Budapest, 2005)
The common history of Lake Balaton and the Sió Canal (1055–2005)
ÁRPÁD VIRÁG The common history of Lake Balaton and the Sió Canal (1055-2005) Lake Balaton owes her recent international reputation largely to the leaflets printed for tourists, in which she is depicted as a body of water situated in a beautiful landscape setting in Hungary with water temperatures up to 25-26 °C in summer attracting bathers to the sandy beaches along the flat southern shore, and sailors to the expanse of open water. Limnologists have been aware for long of the properties, which make Lake Balaton special in both European and global comparison. Outstanding among these are the depth, which is extremely small relative to the size of the water surface, further the wide water regime fluctuations, which threaten to drain all water during spells of dry years and to inundate wide shore strips during wet periods. The only outlet through which excess water can be released to the Danube is the Sió Canal, the headworks of which are at the resort town Siófok. The canal is substantially an improved, regulated natural ancient stream bed, which originated not far from the present headworks, where the rising lake water had overtopped the shore sand dunes at their lowest point and scoured a meandering bed in the Sió Valley. The lake and the canal are thus regarded a single hydrographical unit. Lake Balaton is situated in the western part of Hungary, in the region called Transdanubia, between the northern latitudes 46°62’ and 47°04\ and the eastern longitudes 17° 15’ and 18° 10’, the longitudinal axis being oriented WSW -ENE. At mean water the water surface is at El. 104.80 m above the Adriatic datum (mAf), covers 588 km2, her mean depth is 3.16 m, corresponding to a total storage volume of approximately two thousand million cubic metres (1.9 109 m3). The lake is 78 km long, on the average 7.6 km wide narrowing to 1.5 km at Tihany Straits. In terms of limnology she belongs to the group of large, shallow lakes. Between the Siófok headworks and the tailgate to the Danube, the Sió Canal is 120.8 km long. The catchment area upstream of the Danube tailgate is 14728 km2, of which the share of Lake Balaton and the tributary River Zala is 5755, that of the River Kapos is 3242, the combined share of the Nádor Canal and Lake Velence is 3450 km2. The area drained by the canal directly is 2281 km2 only. The stream network in the catchment is a relatively dense one, the number of streams being 338, of which 137 are in the catchment of the River Kapos, while 116 in that of the River Zala. There is a wealth of archaeological evidence available to demonstrate that the region around Lake Balaton and the Sió Canal had been inhabited since the Bronze Age, some settlements having persisted for several centuries. The Romans have invaded this part of Transdanubia in the 5th decade A.D., and ruled here until 456. They are known to have grown grapes on the southern slopes of the range on the northern lake shore and to have set up a garrison (castrum) on the SW tip, but only a single Roman town, Gorsium-Herculia has developed in the catchment of the Nádor Canal (the former Sárvíz), on the area of the present village Tác, some 40 km away from Lake Balaton and the Sió Valley. The palaces, public buildings, the ancient Christian basilica and the wide streets date back to the 4th century. The results of excavations conducted over several decades in this region, called the Roman Province Pannónia, seem to imply that the climate during the Roman rule was steadily warm, dry and
