Vízügyi Közlemények, 1959 (41. évfolyam)

4. füzet - V. Kisebb közlemények-Ismertetések

(35) ritories, where the natural balance has been disturbed — usually by artificial intoiference of technical chai-cler — and where the groundwater tabiP shows a steady rising tendency (e. g., due to irrigation), or a sinking trend (e. g., due to overexploitation by water works), are an exception to this. Within the range cf gioundwatcr fluctuations — the depth of which is defined by the highest and the lowest groundwater tevel — the artual table is either deeper, or higher, depending upon the influencing factors. Regular changes may be distinguished according* to the periods as daily, monthly, yearly and multi-annuals The hydrological year comprises in general the total perioci of water accumulation and withdrawal. Characteristics of the groundwatei regime can be determined by the systematic compilation of groundwater observation data (Fig. 1 ). In order to obtain a clearer insight into groundwater household, it was then found necessary to establish from among the wide veriety of factors affectine the phenomenon under the given set of conditions, the significant ones, toeether with the relationships existing between the position as well as variations of the groundwater tabie, and the physical, meteorological and other factors. 1. Practical groundwater hydrology was the first to yield results. Methods applied were: quality analysis, graphical methods and analytical investigation. Using the methods of practical hydrology it was found expedient to separate areas, where changes in the stage of adjacent natural watercourses or canals do not affect groundwater conditions to an appreciable extent, from such extending along watercourses. The effect of watercourses is, in general, limited to a more or less narrow riparian stripe. Over the overwhelming part of plain territories groundwater household is in most cases controlled by processes taking place in the close envi- ^ ronment, through the three-phase layer covering the groundwater. Relationships that can be detected between groundwater and meteorological factors, provide information about waterhousehold in similar cases. Some investigators used correlation methods [3 to 8], while others qualitative analysis, [46, 47] to determine the first relationships, on which subsequent Hungarian groundwater research was based. As revealed by results of extensive investigations, two of the various relationships that can be shown to exist between groundwater level, its variations and precipitation, as well as air temperature, are of particular value in deriving conclusions on groundwater household. Most characteristic of groundwater regime is its annual variation. If average variations in groundwater level and air temperature can be considered to approximately follow a sine law (Fig. 2), then the relationship between air temperature and long-term average monthly mean groundwater levels will become elliptical [46, 47, 73, 74], The main axes of the ellipse enclose an angle with the coordinate axes, the value of which depends mainly on the depth of the groundwater table below the terrain. The length of the main axes is controlled by physical properties or the groundwater bearing aquifer, as well as by the width of the range within which average changes in groundwater volume occur. The determination of this relationship presents no difficulties, and, using the numerical value of the angle of inclination as parameter, the time of annual maximum and minimum levels to be expected under average conditions, can be predicted (Fig. 5). The other important relationship characterizing groundwater household is the one between precipitation and rise in level. A unique relationship can, in general, be established for all plain territories between a rise in groundwater level and the precipitation over the same area during the time of the rise (Fig. 4.) Qualitative analysis should be employed in selecting the proper period on basis of which the relation is established. The proper period is, under conditions prevailing in Hungary, in most cases the winter half of the hydrological year. These are the relations that show in the first place the effect of precipitation on groundwater and these lend themselves to quantitative investigations. Depending upon local conditions, and on the depth of the groundwater table in particular, the equalizing line intersects at different heights the ordinate axis, indicating