Vízügyi Közlemények, 1965 (47. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

<85) planning is presented in Chapter II. For determining this method the Sub-Carpathian region of Poland was used as experimental area. The ways and progress of active flood control in Poland are dealt with in Chapter III. Among these the following are to be mentioned: afforestations, establishing rural cultures able to retard the accumulation of waters resulting from rainfalls, flood control storage and multi-purpose storage. Passive flood control, river training, as well as the progress of protection against floods by river levees are reviewed in Chapter IV. Flood control concerned with the Vistula, Oder and Warta Rivers is discussed in detail and a special part is devoted to protection against ice floods. A detailed report is given on the functions of flood control organizations, subjected to the supervision of the General Board of Flood Control, as well as on the activities of regional commissions and other organs in Chapter V. Chapter VI. is connected with the previous one, describing the Flood Control Plan and the objectives and contents of Flood Control Directions issued in every year. COMBINED IRRIGATION BY UTILIZING WINTER DISCHARGE OF STREAMS By B. Sulgok-Schulek and E. Bácsi, civil engineers (For the Hungarian text see pp. 344) Authors performed calculations to determine moisture quantities utilizable by the plants, making distinction between moisture amounts resulting from precipitations of the winter period (from October to March) and from those of the summer period (from April to September). They found that in the flatland area of Hungary lying east of the Tisza River the ratio of these two quantities is 1.6 : 1, both in the case of average and abundant crop yields. This means that moisture amounts of the two seasons are produced by the Nature according to a certain regularity, the rainfall sum of the winter period being considerably greater than that of the summer months. Irrigation practice, however, that is restricted to the summer period only, is not in concordance with this rule. Nature stores winter moisture in the soil. According to authors, in the area under investigation having a part of about 2 million hectares suitable for irrigation purposes, out of the 4 thousand million cu.m precipitation sum a quantity of 3 thousand million cu.m is stored in winter (Fig. 1, diagram No. 2). Based on investigations carried out for several decades, authors have found that in the case of average winter rainfalls the soil is wetted through down to a depth of 50 cm, for abundant crops, however, this increases even to 65 cm. A surplus of about 15 cm of the wetted depth can be produced by an additional storage of 1 thousand million cu.m. This results in an additional moisture amount of 0.8 thousand million cu.m. Penetration depths of minimum and maximum winter precipitations occt rred during 50 years, as well as the wetted depth increased by 15 cm are represented in diagrams No. 1 and No. 3 of Fig. 1. Accordingly, it is the pore volume of the soil, where natural moisture storage is taking place. It is verified by the experiments conducted by authors that in the area under investigation the winter application (in late autumn) of an irrigation quantity of about 50 mm, needed to attain the wetted depth suggested, is free from risks both from the aspect of hydrology and plant physiology. The left-side diagram in Fig. 2 shows in order of magnitude the wetted depths associated with winter rainfalls during 50 years. At an average natural wetting of 50 cm medium yields, at a moistened depth less than 40 cm half as much yields are attained, while at a wetted depth reaching or exceeding 65 cm yields are one and a half times as great, i.e. can be considered as abundant As shown in the figure, in the case of dry farming droughts occur in every 3 or 4 years, whereas abundant crops in every 4 years. According to the right-side diagram in the figure, at an additional wetting of 15 cm droughts do not occur any more and abundant yields are attained in every two years. The winter wetting applied in the proposed measure should be completed with an adequate summer irrigation.