Vízügyi Közlemények, 1959 (41. évfolyam)

4. füzet - V. Kisebb közlemények-Ismertetések

(37) changes in soil temperature. If the moisture content of the soil is above the maximum hygroscopieily, the daily temperature fluctuation in the upper soil layers may give rise to appreciable vapour movement and condensation (Figs. 16 to 19). Vapour moves at high velocities and this phenomenon result in the daily variations of the groundwater table. Direct effects of this phenomenon extend to a depth of about 3 m. Results of both practical hydrology and theoretical investigation show that the main characteristic of the waterhousehold in the plain territories of Hungary is the vertical movement of water through the layer overlying the groundwater table. The horizontal movement of groundwater is usually insignificant and is practically inaccessible to observation. Main laws of groundwater regime were successfully established by the aid of practical groundwater hydrology. This information can be applied to the solution of practical problems. In order to attain more exact results further studies are necessary into the laws governing water movement in three-phase soil, as well as relations concerning heat and waterhousehold in the soil. Vapor movements are considerably more significant than hitherto assumed, and variations in groundwater, as well as in the moisture content of the soil, are greatly affected by water movements in the soil cover. III. Groundwater household and water conservancy No up-to-date water conservation policy can be developed without a clear '• picture about groundwater conditions. The thorough exploration of these conditions for every particular territory and region is the prerequisite to the solution of technical problems related to water conservancy. This requirement is met by a series of geohydrological maps, which show the average and extreme positions of the groundwater table, the average and extreme fluctuations in groundwater, the extent of variations in groundwater volume, data on water quality, boundaries of areas with groundwater types of identical character, and characteristic data on groundwater regime and groundwater household for these areas. Practical water conservancy should, furthermore, collect continuous information about actual groundwater conditions. This purpose is served by groundwater bulletins wich can be prepared periodically. The monthly groundwater bulletin prepared for the Great Hungarian Plains is shown in Fig. 20. lsomctric lines in the map indicate the deviation of the mean groundwater tabic for the month in question from the long-term average groundwater table in the same month. ' Groundwater forecasts can be prepared without undue difficulty. Forecasts predicting the expected highest groundwater table in Spring, and in anticipated duration, have already been issued for the last few years regularly in Hungary. The approximate, distant forecast is prepared in December of the antecedent year, while the more accurate one in February, on basis of the groundwater situation in autumn, by the aid of the relations described previously [76]. Groundwater forecasts for the spring provide, on the one hand, valuable information for agricultural planning, and, on Llie other, hints as regards the extend of protective measures against excess surface waters. Simultaneously with the forecast, territories where complete saturation of the soil is to be expected, can be defined (Figs. 21 and 22). Having established the relationships governing natural groundwater regime, changes in groundwater household, which result from various technical measures, can be determined. Effects of riceirrigation (Figs. 24 and 25), of plain-land reservoirs (Fig. 26), and of river barrages (Fig. 27) on groundwater have been investigated in the i'iist place in Hungary [27, 75]. The consideration of groundwater conditions appears to be indicated in various branches of hydraulic management from the following aspects: a) In case of flood protection the extent of underseepage under levees, as well as the pressure acting from below on the soil cover on the protected side, are appreciably influenced by the position of the groundwater table in the period preceding the flood (Figh. 29). b) Information concerning the origin and runoff of excess surface waters can be gained by a careful waterhousehold analysis. Seasonal variations in the runoff coefficient and, in turn, in the specific runoff volume, are due mainly to differences