Vízügyi Közlemények, 1966 (48. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(99) ESTIMATION OF THE PROBABILITY OF HYDROLOGICAL EVENTS WITH THE HELP OF DISTRIBUTION FUNCTIONS By Dr. Z. Szígyártó, Civ. Engr. (For the Hungarian text see pp. 453) In modern designing practice various hydraulic structures serving resources development are based on rainfall volumes, flood stages of a certain predetermined probability, or more broadly, on hydrological events of different probability. Still in Hungarian engineering practice exact methods of mathematical statistics have not found any widespread application, due mainly to deficiencies of education in this respect. These methods, on I lie other hand, would be necessary for the analysis of basic data relating to these events. The great exactness required in solving practical problems calls urgently for the application of a reliable method free from subjective errors. With these considerations in mind an attempt is made herein at reviewing methods of mathematical statistics suitable for estimating probability from long records, and at describing the practical performance of relevant calculations. Keeping in mind requirements of practice, rather than emphasizing mathematical verification, a summary of basic concepts and the demonstration of most practicable and most commonly applied methods — illustrated by examples — is endeavoured. With this approach, following the summary of fundamentals of probability theory and mathematical statistics, detailed attention is devoted only to the estimaton of the probability of hydrological events which can be described by normal and gamma distributions. The practical determination of parameters necessary for calculation, together with the investigations involved, is demonstrated in this context. To facilitate practical calculations the necessary tables are also attached. ON THE SEDIMENT TRANSPORTING CAPACITY OF STREAMS By Dr. Z. Hankó, Civ. Engr. (For the Hungarian text see pp. 481) Sediment transporting capacity is understood as the greatest sediment load, which any particular stream is capable of carrying. The magnitude thereof depends on the hydraulic and geometrical characteristics of the watercourse, further on the geometrical and material properties of the sediment. The greater part of the sediment is carried in suspended form, while the smaller part as bed-load. Investigations into this phenomenon of Nature after the results obtained by Lane, who laid the foundations for modern sediment research by developing the theory of the stable bed. The statement that problems of flow and sediment movement cannot be considered separately, should be regarded as of basic significance. For determining sediment transporting capacity the conveyance of bed-load must be described first. The specific tractive force of a watercourse is still calculated using the formula of Du Boys (1). At values smaller than the force required for setting the sediment into motion, the sediment remains stationary, and at higher values it is transported. The general form of the tractive force characteristic of the regime of sediment transportation is given by Eq. (2). For different boundary conditions of sediment movement, the relationships between dimensionless invariants characteristic of the initial staye of movement and the instability of the boundary layer in the moving fluid have been determined by Liu, Albertson, Simons and Richardson. The general form of this relationship is expressed by Eq. (3). This was rewritten by Bogárdi (for water of 20 Centigrades temperature and 1.00 g/cu. cm specific gravity, and sediment of 2.65 g/cu. cm fl Vízügyi Közlemények