Vízügyi Közlemények, 1998 (80. évfolyam)
2. füzet - Liebe Pál: A hévízhasznosítás helyzete Magyarországon
224 Liebe Pál loss of hydraulic head, depression, in the reservoir. Upon the effect of the loss of head colder and usually more polluted waters start to flow into the system, resulting in cooling down and contamination of the water of the thermal reservoir. The result of the regional and local losses of hydraulic pressure in the thermal water reservoirs is that the well-head pressure of newly drilled wells will decline rapidly. This also means that the number of negative wells, where the stagnant water level of the well had not exceeded groundlevel, not even at the time of its boring, is increasing (Figure 6.). Not even the half of the wells, which have been established after 1985, were positive. Surveys of 1996 also indicate the loss of hydraulic heads and the turning of wells into negative ones. Summarizing the results of the regular periodical survey and review of thermal wells it can be stated that in the shallower than 500 m deep thermal water bearing strata of the Alföld (the great lowland plains of Hungary) the loss of head was 0.2 m-0.3 m (average 0.6 m), it was 0.3—1.1 m (0.6 m in average) in the depth domain 500-1,000 m and the deeper than 1,000 m zone is characterized by 1-2 m/year decreasing trend. Trends of similar magnitude have also been observed in the Kisalföld. In the vicinity of the thermal water wells of the Dunántúl (Transdanubia) the rate of decrease was about 0.5 m/year. The loss of head is uniform over the thermal water reservoirs of the Alföld. Figure 7. shows the water level time series of two relatively distinct observations wells. It can be seen that the uniform trends of decrease of the 1980-ies became more moderate by the 1990-ies. The deeper wells of the national hydrographie network show similar trends (Figure 8.). Discharge and pressure conditions of thermal karsts of the mountain rims can not be investigated without the interconnected cold-water karstic reservoirs. Figure 9. shows the discharge of the thermal karsts of Budapest and Hévíz, along with the water levels changes of the karstic reservoirs in their vicinity. It can be seen for both cases that the decrease of the pressure heads of the karstic system has been halted, mainly due to the decrease of mine dewatering and thus to the closure of mines. In the case of Budapest the karstic water levels show moderately increasing trend, while in the case of Lake Hévíz the karstic levels are stagnant but the discharge of the spring of the lake is increasing. Loss of pressure of thermal karstic reservoir, upon the effect of water abstraction, can be avoided or alleviated with recharging the spent thermal waters into the reservoir, after utilization. International experiences with the recharging of used thermal waters indicate that there is no problem with the recharge into fractured rock. However, no reporting on operational cases concerning recharge into sedimentary clastic formations are known to the author. There were some experiments in Hungary with the recharging of used thermal waters, with lower pressure, into the aquifers. On the basis of these experiments thermal water recharge plants have been established, and are operational, in Hódmezővásárhely, Szentes and Szeged. An outstanding example of these is the Geothermal Heating System of Szeged-Alsóváros, where a pair of wells of inclined boring are in operation for abstraction/recharge. At 50 mVh recharge rate the initial pressure of 0.3-0.4 MPa has rapidly increased to 1.5—19.9 MPa. At the Szentes and Hódmezővásárhely recharge plants the same wells serve for both abstraction and recharge. The used water is being recharged into an aquifer of higher elevation. These experiences indicate that recharge into clastic porous formations is not without problems. Due to the limitation of natural recharge of aquifers the water- and environmental authorities do not release new permits for thermal water abstraction, for solely energetic purposes, without solving the recharge of spent waters. Even existing abstractions must be sparingly operated. To ensure this, the authorities apply economic regulation in the form of an extra charge on the use of water resources. Its magnitude depends on the method of utilization. There is a minimum charge for medicinal and balneological utilization, while the rest of the users pay a charge of the magnitude of several times this minimum rate. The minimum rate is 1.15 HUF/m 3. The multiplier, which depends on the method of utilization and on the type of the water resource, is given in Table 111. The law specifics that no charge is to be paid for the fraction returned via recharge to the aquifer.
