Vízügyi Közlemények, 1974 (56. évfolyam)

2. füzet - Kovács György: A felszíni lefolyás általános vizsgálata és az árvizek előrejelzése. II. rész

A felszíni lefolyás vizsgálata 245 the channel, the definition and estimation of the time of passage, the clearing of the phgsics of flood- and surge waves and in this context the applicability of wave celerity as a boundary condition, further the superimposement of ci flood wave of the rising ancl falling branches may be mentioned as problems awaiting to be solved in the near future. 7. Determination of the design flood level In the cross-sections for which records of adequate length and reliability are available, the statistical analysis of data is in general applied for estimating the flood stages, or discharges anticipated at different levels of probability and the parameter to be adopted as the design value is selected on the basis of economic considerations involving also the time of recurrence. Regardless of the fact that the hydrological aspect of the problem, namely the determination of the flood parameters anticipated at different levels of probability has already been dealt with in countless papers in the relevant literature and that the methods to be applied have been standardized in several countries, research into the problem cannot be regarded as terminated. The uniformity of the record, the selection of a possibly large number of independent sample elements from the records containing daily observation data for the population examined statistically, further the selection of the best fitting distribution function are among the still open problems. Research has been conducted 011 each of the three subjects and the results attained are of considerable interest. The very fact, however, that the debates on these problems continue with unchanged intensity indicates the failure of finding an entirely satisfactory solution. The classification of the records according to the type of precipitation triggering the flood (selection of a uniform sample according to the cause) and in order to counterbalance the resulting reduction of sample elements the inclusion of every flood peak exceeding a certain level, further a physically justified selection of the type of distribution function may be suggested as objectives of further research. Beyond the estimation of flood stages or discharges pertaining to different levels of probability it is believed desirable to determine additional statistical parameters as well (e.g. the probability of the period between two successive flood waves). Research 011 such problems has already been started and the continuation of work is recommended. The estimation of design flood parameters presents special problems in catchments, where no long, reliable reccrt!s are available. In order to estimate the characteristics of such sections, attempts have been made in Hungary in determining correlation between the parameter values and the size of the catchment. As a conclusion of research work relationships have been suggested, hut these must still be checked against a large number of records before maps covering the entire country and indicating the areal distribution of the various parameters can be constructed. 8. Research related to the modernizing of flood data acquisition Besides the solution of a number of problems related to measurement and automation, a problem of hydrological character must also be solved in the interest of reliable flood data collection. On the Hat rivers in Hungary, where the slope pertaining to the rising and falling stages may differ by as much as ±80% from the mean value, the determination of three-variable discharge relationships (discharge, stage, slope) assumes paramount significance. Owing to the wide differences, the loop formed by the rising and falling branches of the rating curve (stage-discharge relation) is a very wide one, so that widely different discharges may pertain to the same stage. The present uncertainty of the discharge statistics cannot be eliminated, unless allowances can be made for these differences. The theoretical investigations related to the three-variable stage-discharge relations have been started long ago and may be regarded as more or less terminated. The only major obstacle to their introduction into general practice is the inaccuracy of slope measurement. As a remedial measure the installation of auxiliary gages