Vízügyi Közlemények, 1975 (57. évfolyam)
1. füzet - Wisnovszky Iván: A települések csapadékcsatornázásának hidrológiai vizsgálata
A települések csapadék-csatornázása 41 of the duration of the rising branch on the unit hydrograph are plotted in Fig. 4 (after Eagleson ) for different stages of urbanization, in terms of the catchment area coefficient K. The same diagram indicates the observed peak discharge of the unit hydrograph in three gaging sections on the urban experimental catchment at Miskolc, Hungary, determined from measurement results. The increase in runoff due to urbanization is shown alter Seaburn in Fig. 5. One of the mathematical models developed in the US for estimating the hydrograph in urban sewer systems is described, with the block diagram of mechanical computation illustrated in Fig. 6. In Section 2, in describing the research activities in Hungary, the experimental urban catchment created in 1972 at Miskolc is presented. The area of the catchment is 74.7 hectares, in the center of which a reporting gage has been mounted. The stages are observed by means of four automatic, float controlled potentiometer gages. All electric signals are transmitted to a 16-channel point recorder manufactured by Kent Ltd. In this way the precipitation — and stage records are synchronized. The layout of the catchment is shown in Fig. 8. In the experimental catchment the impervious surfaces have been determined by a detailed survey and the functions of infiltration time (Horten curves) shown in Fig. 9 have been found by actual measurements. For the three gaging sections in the experimental catchment the momentary unit hydrographs generated by a storm runoff rate of 1 mm/minute have been estimated (Fig. 10.). Using these all flood hydrographs observed have been compared with the theoretical hydrograph. One of these simulations is illustrated in Fig. 13. The problems associated with the rational method used extensively in designing urban storm sewers are analysed in detail in Section 3. IL is concluded that the runoff coefficient, which plays an important role of transformation in the method has been made accessible to computation as a result of recent research results and that the method of computation has been verified by the results of research on urban runoff hydrology in Hungary. The results have opened the way for developing an analytical method of storm runoff computation, by which the peak discharge in a hydrograph resulting from a particular urban catchment can be estimated. In the first stage the method is suited for estimating the peak discharge for a 10 heclares unit of the area considered, for which reason it is referred to as the specific hydrograph analysis. The simplifying assumptions involved in the method make any resolution of the area considered into such units superfluous when performing actual computations. The data needed for applying the method include the size and average slope of the catchment, the length and average slope of the longest runoff path, the time of accumulation and the input parameters of the generating storm. With these data available the diagrams shown in Figs. 12. and 13. can be used. The degree of approximation attainable by the specific hydrograph analysis is better than in the rational method, moreover the runoff hydrograph can also be determined. With reference to Fig. 14. the relationship between the service life of the sewer network, the recurrence probability of the design loading and the risk of damage is analysed. It is demonstrated finally, that under a low head the storm sewer network is capable of conveying a substantially greater discharge than that adopted as critical in the designing stage. In conclusion, the results of research abroad into urban hydrology, which are considered applicable in Hungary, are listed. The application of the unit hydrograph method is suggested and recommendations are given concerning the practical application of the rational method and of the specific hydrograph analysis. * * *
