Vízügyi Közlemények, 1999 (81. évfolyam)

2. füzet - Pannonhalmi Miklós: A Fertő-tó vízgazdálkodása

292 Pannonhalmi Miklós Water management of the Lake Fertő by Miklós PANNONHALMI C.E. Lake Fertő is a lake of unique natural features, the largest and western-most steppe-lake in Europe. The lake is located on the country border between Hungary and Austria, shared by the two countries (Fig. 1.). Its extent has changed several times during the past centuries, as indicated by the relevant historic documents. The water management of the lake has been under the auspices of the Rába-szabályozási Társulat (Association for the Regulation of the River Rába) and of its successor, the Észak-dunántúli Vízügyi Igazgatóság (North-Transdanubian Water Authoring) since 1873. Operation is maintained at the Hydrometeorological Station, which is located at the lake-side (Fig. 2.). National parks were established in 1991 and in 1993 on the Hungarian and Austrian side, respectively. Thus, the lake is subject to the highest level of nature conservation regulations. Climatic conditions of the lake are demonstrated by the figures (Figs. 3—6) of air-temperature, lakewater temperature anomalies form the multiannual mean, winds and of the annual precipitation. Catchment areas and mean flows of the rivers feeding the lake are shown in Table I. Table II. presents the multiannual water budget of the lake. The lakes water regime varies within extremes. Stabilisation of this variation was started on the end of the last century and completed in the begining of this century with the dams built into the main-canal Hanság (Fig. 7.). Compliance with the regulation rules of the gate of Mekszikópuszta allowed the rising of the lake's water level by nearly half a meter, in 1965 (Fig. 8.). Reconstruction works of the water system also included that of the barweir of Mekszikópuszta (Fig. 9.). The two countries have jointly developed the new regulation rules of the sluices and weirs. The ratio of lake surface area to open water area defines the character of the lake. This ratio is summarized in Table III. Regulation of the lake's water level helped suppressing the propagation of the reed zone (Fig. 10.). Dense network of canals were constructed for utilizing the lake's water resources. An example of this is shown in Fig. 11. The water quality of the lake also reflects the special natural conditions. Regular monitoring started only in the 1970-ies, although investigations started much earlier. Variation of the salt content of this "natron-lake" is shown in Fig. 12. High organic content of natural origin characterizes this lake. This results in unfavourable oxygen conditions in the water of the reed-zone. The nutrient content of the lake is low and the phosphorus concentration was decreased by control actions made on the catchment basin (Fig. 13.). Future water management tasks are defined by the recreational use (Fig. 14.) of the lake and by the nature conservation requirements. Implementation of these tasks represent a serious challenge to the water management specialists of both countries. * * * Wasserwirtschaft des Neusiedlersees von Dipl.-Ing. Miklós PANNONHALMI Mit seinen ganz einzigartigen Naturgegebenheiten ist der Neusiedlersee (ung. Fertő) das größte und sogleich westlichste Mitglied der Gruppe der sog. Steppenseen. Er erstreckt sich teilweise auf österreichischem und teilweise auf ungarischem Staatsgebiet (Bild 1). Seine Flächengröße hat sich während der vergangenen Jahrhunderte oft verändert, wovon historische Dokumente zeugen. Für die Behandlung der mit dem See zusammenhängenden wasserwirtschaftlichen Angelegenheiten war ab 1873 der Verband für Raabregulierung, bzw. sein Rechtsnachfolger, die Wasserwirtschaftsdirektion Nord-Transdanubien zuständig, wobei letztere ihrere Aufgaben z.T. über ihre, am Seeufer befindli-