Deák Antal András: A Duna fölfedezése
Tartalom - III.A DANUBIUS PANNONICO-MYSICUS, 1726
T II E DISCOVERY OF THE DANUBE exists a flow of underground waters in the Hungarian Plain. Thus, Marsigli's hypotheses about the ground current from 300 years ago seems to be confirmed. 27 9 He also realised that it was not only the rivers that fed the swamps but that this process worked in the opposite direction as well: The river feeds the swamps through channels called fok, or flows over the above-mentioned lines and cuts itself reservoirs where the excess water from the huge river is retained for a few days before flowing from one territory to another; namely, it has to fill them up first. He observed this phenomenon in July 1694 when he was stationed with the army at Culut (Kula?). He received threatening news from Vienna about the flooding of the Danube, yet there was no trace of the flood although it should have arrived in a short time. He explained the phenomenon by the fact that the flooding river first had to fill the swamps. This water retaining capacity of swamps is important when water was low as well. It is also due to these swamps that the mass of water in the actual bed of the Danube does not start receding obviously, quickly and instantaneously even though the rains and the melting of the snow, the causes of the flood, have already stopped; namely, the waters seeping back from the swamps into the Danube postpone the dropping of the water level. He also realised the destructive, compounding effect of the various barrages. In these cases, the current of the river becomes unsteady, and islands or new swamps develop. Among the barrages he mentioned locks, dams, strong bends and straits. He illustrated in a picture how the water flows in and out of the swamps through the channels called 'fok' at high or low water. The picture on page 81 and its legend make it evident that he regarded these channels as natural phenomena, an umbilical cord between the river and the swamp: If the level of the water in the Danube would drop down even below level C, a new channel would develop, and so it would go until it reached the level of the bottom of the lake and masses offish would perish, poisoning the very air. In his description he also mentions that these channels are not formed by the flood that inundated the floodplains at high water but by the mass of water covering the lower terrain during the high water period. Phis water sought its way back into the river when the water level drops. It always pushes toward the deepest parts of the terrain, feeding swamps in the depressions, and building itself basins depending on the ground features in the area until it finds its way back to the river. 280 His theory is corroborated by recent observations as well. 28 1 He would have liked to have been able to show variations in the water level of the Danube as well: at low, medium and high water. Lacking a water gauge, however, he could illustrate them only in relation to the depth and the cross-section of a given river bed. He marked the month and the year observations of the water levels were made. He measured the highest water mark in June 1694 and the lowest one in AugustNovember, 1693. When he had the luck to go to the northern part of the country, to Rimaszombat in the spring of 1693 and to the mining towns during the winter camp of 1694-95, he was already working on his Danubius. Since the waters of the springs that well up here also run down to the Danube, he found it necessary to deal with the sulphuric springs of Hungary, which are believed to be poisonous. He had seen something similar to the springs in the northern part of the country and in Transylvania during an excursion in his youth: A small hole can be seen near a lake called dAgnan near Naples, which is covered to the height of about 1 foot by a fog-like vapour 27 9 Deák Antal András: A földárja (The Ground Current). Élet és Tudomány vol. LV. No. 11. 17 March 2000. 28 0 Deák Antal András: Fokok és árvizek. (Fok channels and flood waters) Élet és Tudomány vol. LV. No. 23. 9 January 2000. 28 1 Dr. Tóth Albert, professor at the Sámuel Tessedik High School (Mezőtúr) observed them in May-June 2000 as the flood retreated at Szajol and Tiszavárkony. The former is 10-40 m broad, the latter 15-20 m wide. He wrote the following about the way they developed: a large mass of water broke through the left side of the river bank as it headed from the floodplain gulf back into the river at Szajol. Consequently, the channel was evidently opened up by the erosion of the retreating water. (Manuscript). 145