Vízügyi Közlemények, 1973 (55. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

flood waves rushing down the mountains overtook each other in the plains, where they became superimposed. Typical data on the regime of rivers are shown in Table I. Today the difference between the highest and lowest stages in the Tisza River over the Hungarian reach is 10 to 12 m, and attains 7 to 8 m even on the tributaries. As a consequence of human interference, stage fluctuations in the Tisza River have increased by as much as 5 to 6 m during the past 150 years. The discharge in the Tisza River ranges from 50 to 4,700 cu.m/sec. The runoff volume annually passing the cross section of the Kisköre Barrage is 8 to 10 thousand million cu.m in dry years and 36 to 38 thousand million cu.m in wet years. As a consequence of bend-cutting and confinement between levees the flood stages have become higher, ^while flood waves have travelled faster than before regulation. The basic aims of water management are defined by the aforementioned hydrological properties and consist af reducing the fluctuations in water level and in discharge, further of regulating and making accessible for diverse uses the waters travelling down at high rates in the channels. The fundamental means of such control are barrages creating channel storage and flood plain storage. The climate is basically continental in character, but occasionally Mediterranean and Atlantic air currents become predominant. The regular alternation of wet and dry seasons is attributed to this circumstance. In general, 2 to 3 arid and 2 to 3 wet years have been recorded in every decade. The average annual precipitation in the plains is less than 600 mm and in large parts even less than 500 mm. In drought years the rainfall in the growing season may be as low as 170 mm. The aridity factor, i.e., the ratio of potential evaporation to precipitation, which is of fundamental importance for plant growing, ranges from 1.2 to 1.4. The distribution in time of precipitation is adverse also to agricultural production, in that lowest discharges occur primarily in the summer, at the peak of the irrigation season. The alluvial soils in the plaints are not uniform in quality, with wide differences in permeability. The depth of the groundwater table below the terrain is in general from 2 to 6 m. In this region a primitive method of water farming adapted to the prevailing natural conditions had evolved before the regulation works. This nevertheless played an important role in mediaeval economic life. "Ancient flood plain farming" was practiced as early as in the 13th

—14th centuries, including fishing, stock raising based on storage irrigation of meadows, the operation of mills, water transportation, the production of building materials and raw materials for domestic industries, as well as flood plain orchard cultivation and forestry. Ancient flood plain farming deteriorated in the 14th to 17th centuries under Turkish rule. After the resettling of the plains, started in the 18th century, development was frequently interrupted by famines and losses of stock in the wake of droughts or by the shortage of corn after floods. By the beginning of the 19th century it was generally recognised, thanks to the unrelenting efforts of the great Hungarian politician Count István Széchenyi, that the regula258