Vízügyi Közlemények, 1972 (54. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(58) In the course of historical development the protective zone, necessary for conserving the yield, temperature, chemical composition, etc. of the thermal waters, was assumed with gradually increasing sizes ( Fig. 1). In earlier recommendations on the size of the protective zone the problem was approached from the deterioration of the medicinal character of the water and from the aspect of immediate interference between the individual sources. Individual protective zones of circular shape and of the same magnitude were assigned for sources of different yields, without taking into consideration, however, the magnitude, or/and direction of the factors provoking changes. It should be realized in tracing the boundary of protective zones what influences are to be averted by a particular boundary line. The changes and effects considered undesirable should be understood and specified. Problems associated with different types of protective zones are discussed subsequently. 1. Primary hydraulic protective zone is understood as the area within which any new withdrawal results in an immediate considerable reduction in the yield of existing springs and wells. The simplified flow pattern shown in Fig. 2 is used to derive Eq. (1), from which the flow velocity of the thermal component assumed to have a temperature of 80 °C and streaming in the reversed direction is estimated by substituting realistic values. Using the velocities and distances thus obtained it is possible to estimate the time at which any pollution (occasionally radioactive) entering in the catchment may be expected to appear in the springs, or boreholes. The yield and average temperature of the reverse flow indicated in the figure may differ for the groups of springs taken into consideration [Table I, Eq. (2)]. Around the boreholes sunk into the covered karstic rock an independent depression was found to develop within the uniform flow field (Fig. 3). The magnitude thereof is found from Eqs. (3) and (4). Primary hydraulic protective zones may be estimated with the size thus obtained. 2. Secondary hydraulic protective zone is the term used by the author to denote the area, within which any new withdrawal results in a rapid drop of the piezometric level in existing springs. Of course, in succh cases there is also a drop in yield corresponding to the Q-.H curve. The influence ranges are determined in this case from the data of pumping tests at the individual withdrawal points, with the other boreholes closed and used only for waterlevel observation. Tests performed in this manner indicated 0.5 to 1.0 m drops in the piezometric level even at distances of several kilometres. In some instances the influence became apparent within a few minutes already, whereas in others after one, or two days only, depending on the structural lines along which the boreholes communicated. 3. There is a definite need for expanding the concept of the hydrological protective zone. Any major depression created beyond the catchment area of the springs is bound to affect the subsurface catchment itself, reducing its magnitude and in turn the spring yields. An increase of no more than 10 m

3/sec in the rate of pumping at the Dorog coal mines, situated at round 30 km distance from the thermal springs of Budapest, was demonstrated to cause a drop of about 0.1 m in the stationary level in the boreholes drilled for exploring these thermal waters. The spreading depression caused by several decades of pumping was demonstrated to have reduced considerably the original subsurface catchment area of the springs. 4. The magnitude ol the thermal protective zone for the Budapest thermal springs yielding daily about 70 000 m

3 of water at an average temperature of 36 °C has been estimated at 615 [4] and 1134 [10] km

2 on the basis of different theoretical assumptions and of values of the heat flux originating from the Earth. The boundary of the thermal protective zone should be traced starting from the line of the springs (the intersection of the open- and covered karst) in the covered karst formation. BRIEF PUBLICATIONS AND REPORTS 1. Starosolszky, Ö., Dr. Engr. : The VIII. Congress of the International Commission for Irrigation and Drainage at Varna (For the Hungarian text see pp. 322) The VIII. International Congress of the International Commission for Irrigation and Drainage, 1С ID, was held from the 17th to 28th May, 1972 in Varna, Bulgaria.