Vízügyi Közlemények, 1944 (26. évfolyam)
1-4. szám - IV. Szakirodalom
(6) In order to compute the rate of run-off we must know the regularity of the precipitation involved, we have to determine the actual fraction of the precipitation drained off, and finally we must find out — for the purpose of selecting the maximum discharge — the phenomena of the run-off. 1. Determination oî the regularity oî the precipitation and selection of the competent rainfall. In computing the rate of run-off the determination of the amount and duration of the rainfall is most important. After a review of Hungarian literature concerning precipitation conditions (Bogdánfy, Korbély, Kenessey, Németh), the research works of some of the outstanding foreign scientists (Iskowszki, Lauterburg, Pascher, Specht) as well as the works of the Italian scientists (Pwppini, Fantoli, Poggi, Frosini, Forti, Kambo, Montanari) are made the subject of this study. The Hungarian Korbély expressed in 1915 already in definite form, still in use at this time, his belief that the duration of rainfall and the amount of precipitation are related. He has tabulated the amount of rainfall for the duration of from one hour to five days (Table I). In Hungary the drastic decrease of rainfall by the increase of the duration is determined in mathematical terms with the most commonly used Montanari probable climatic function: h = a T n . However, if we consider it essentially it is identical with the Korbély law, only the determination of the one day rainfall (a) and exponent n is new. The competent, i. e. the critical rainfall resulting the maximum run-off is not of the longest duration nor the most violent. The competent rainfall may be found somewhere between the extremities of rainfall and duration dependent on the individual conditions of the drainage area. The Montanari probable climatic functions are deduced in this study for areas in excess of 5000 ha = 12.300 acres. The method used is shown on the drainage area of 1448 km 2 belonging to the Sárszentmihály gage at the Nádor canal (Fig. 1.). The intense precipitations were grouped monthly from the records of the rainfall station during the period of observation (1932 to 1941). Table II for example consists of the data of the month of February, on the basis of which the maximum rainfall of one day, then of consecutive two, three days etc. were computed on all stations. Table III contains the derived rainfall series on each station on the basis of wich it may be determined from Table II the date of the competent rainfall regard to the entire drainage area. Consequently the rainfall between February 19 and 26 of 1936 may be considered as maximum rainfall series. With Table IV the computation of the maximum February rainfall series may be performed without difficulty on the basis of average values for the whole drainage area. On the basis of rainfall series, stated on page 17, the determination of the probable climatic function for the month of February is shown in Fig. 2. In the rest of the months similar to the month of February the established rainfall series and the probable climatic functions, are exhibited in Table V. These rainfall series, however, are not of equal value from the point of view of the down flow since the run-off coefficient varies from month to month too. The rainfall series — reduced by the run-off coefficients determined in the forthcoming (Table XVI), — may be compared by now and is shown in the text set in italics of Table VI. Ultimately the most critical rainfall series and the probable climatic function derived therefrom are exhibited in Table VII. The dependability of the Montanari function may be increased if the same is deducted from rainfall records of longer periods. We examined the maximum rainfall series of the years 1912 to 1931, of 1932 to 1941 and of 1912 to 1941 of the Közép-Tisza Flood Control Society drainage area. There appear only slight discrepancies within the 10, 20 and 30 year periods (Table VIII). In order to save time we shall therefore refer in the forthcoming to the data of the years of 1932 to 1941. Table IX covers constants characteristic of the regularity of the precipitation on twelve more drainage areas. 2. Determination of the run-off coefficient. The run-off coefficient is the ratio of the quantity of water drained off on the surface, Qf and the water quantity in the form of precipitation, Q e. It has two limits — the unity and the zero.
