Vízügyi Közlemények, 1997 (79. évfolyam)

2. füzet - Szabó Mátyás: A Velencei-tó vízháztartása

188 Szabó Mátyás Water budget of Lake Velence by Mátyás SZABÓ C.E. With its 24.2 km

2 surface area Lake Velence is the third largest natural lake of Hungary and a favoured target resort of internal tourism (Figure I.). Hundred thousand visitors seek recreation and water sports along the shoreline and in the water of the lake. The water budget of the lake is unbalanced, since inflow from the drainage basin is fluctuating and rather low. Data of the geometry of the lake are given in Table /., while Figure 2. shows the hydrological characteristics. It is a characteristic historically recorded feature of the lake that it had run dry several times in the past centuries. Records of the regular hydrographie observations, available since 1931, also indicate periodically occurring very low water stages. Recreation seeking mass-tourism started in the 1970-ies. Water level regulation was facilitated by the construction of two reservoirs on the catchment area (Table II.) and by extensive shore-line and lakebed regulation and protection works (Table III). Later the landscape of the lake side has ben substantially changed, large recreational resorts covering both the northern and the southern shores. Drought period occurred again in 1988—93 (Table IV.) in the catchment area of the lake upon which the level of the lake surfaces reached critical state, that could not be counteracted by the operation of the reservoirs (Figures 3-4). In order to solve the water budget problems of the lake (Table V.) a water diversion system has been constructed in 1993, which supplied additional water of 11.3 million m

3 to the lake during 3 years. With this man made supply system and upon the effect of wetter years the water budget of the lake has been improved. Lake water levels and artificially supplied additional inflows are shown in Figure 5. for the period beyond 1993. The water Resources Research Centre VITUKI has made several studies for evaluating the events of this dry period and made several proposals for protecting the lake's water budget. Some of the most important measures made on the basis of these proposals were as follows: 1. The rules of lake water level regulation have been changed (Table VI.); 2. A joint set of operation rules has been elaborated for the lake and the two reservoirs of the catchment; 3. The allowable water abstraction from the lake has been redueed to 1.5 million m

3/year; 4. An environmental and water management monitoring system has been established for the lake. The lake's water budget has been fully reestablished in 1995 and 1996. In the spring of 1997 the reservoirs were filled to 90% of their total storage capacity and the surface water level of Lake Velence is now at its optimum. On the basis of the evaluations and proposals by the experts the adverse effects of similar weather conditions can be counteracted and reduced, provided the new rules of water budget regulation are complied with. * * * Wasserhaushalt des Velence-Sees von Dipl.-Ing. Mátyás SZABÓ Mit seiner 24,2 km

2 großen Wasserfläche ist der Velence-See Ungarns drittgrößter natürlicher See. Er ist ein beliebter Zielpunkt des ungarischen Erholungstourismus (Bild 1). Während der Sommerzeit wird sein Ufer und seine Umgebung von hunderttausenden besucht, die sich dort erholen oder dem Wassersport ftöhnen.