Vízügyi Közlemények, 1967 (49. évfolyam)
4. füzet - Rövidebb közlemények és beszámolók
(4 3) The above values, shown in columns 24, 11, and 20 of Table I, have hereafter been analysed by the author for each district water authority. Two-variable correlations were first established between the three factors. The relationships between В and qs, as well as between e and qs are shown by Eqs. (8) and (9), respectively. For degrees of development lower than qs = 12, Eq. (9a), for higher ones Eq. (9b) should be used. Relationships have been determined by graphical correlation according to Figs. 3 and 4. Relying on these two relationships, a direct relationship has been determined in Fig. S between В and e (continuous line, scaled with respect to qs), and using graphical correlation in the logarithmic plot of Fig. 6 the relationship expressed by Eq. (10) has been found (shown to an arithmetic scale by the dashed line in Fig. 5). In Fig. 3 the curve representing the relationship between В and qs has also been provided with a scale referring to e. The graphical plot thus completed, as well as the curve scaled in Fig. 5 with respect to qs are thus representative of the relationship expressed symbolically in Eq. (6). Examinations by the author extended to the determination of percentage differences of values calculated by these relationships with respect to basic data, and to the results calculated using the same relationships in combination with data on part areas inundated for each district authority (these having been available only with sufficient detail). These latter results agreed fairly well with data on total areas. Values determined by calculation and percentage deviations thereof from known values have also been entered in Table 1. These checks provided satisfactory proof for the reliability of the relationships introduced. Considerable deviations were, however, observed — as expected in view of the simplifications introduced in connection with the factors ht -in the case of areas with more permeable soils, where both the volume of excess surface water removed, and the inundation index were lower by orders of magnitude than calculated ones. From the checks it was found further that in the case of high degrees of development qs the actual index numbers were higher than those calculated using the above relationships. The explanation offered for this circumstance is that in cases, where extreme excess surface waters similar to that encountered occur in very highly developed systems, inundation damages are controlled no more by the degree of development, but by usually neglected low-order drainage works (maintenance of low-order drainage ditches and their culverts, connection of depressions to these by trenches, etc.). Consequently, the improvement of qs beyond a certain limit, is no more capable of reducing inundation damages if low-order drainage works are omitted. Discussion of results, conclusions Relying on the results desribed above the following conclusions have been arrived at: a) The combination of meteorological factors infuencing the development of excess surface water inundation resulted in extreme conditions. b ) For this reason the influence of local factors (type of soil, topographic relief, position of the groundwater table, etc.) affecting the development of excess surface water lost its dominance over the majority of plain-land catchments of the country. c) Roth the index calculated from the magnitude of area inundated and the weighted duration of inundation, as well as the volume of excess surface water removed artificially, revealed positive relationship with the degree of development, which represents the extent of human interference. The proportionality is in the first case an inverse, whereas in the second a direct one. d) It could be demonstrated that the extent and weighted duration of inundation vary inversely as the fourth power of volume of excess water removed artificially. In other words, if it is desired to minimize in extreme cases similar to those studied, inundation damages, then the volume of water removed must be increased in proportion to the fourth power. e) The above conclusion holds true up to a certain degree of development only, beyond which the reduction of inundation damages depends primarily on the execution of low order drainage works. At times of smaller excess surface water volumes the role played by these becomes dominant even at lower qs values.
