Vízügyi Közlemények, 1944 (26. évfolyam)

1-4. szám - IV. Szakirodalom

(?) The correct discernment of the run-off coefficient is the result of lengthy research work too. More recently the run-off coefficient was calculated by average values. Bogdánfy (1906), for instance expressed the yearly discharge in the river beds in percentual fractions with respect of the annual rainfall (Table X). Subsequent research workers, however, determined the run-off coefficient as function of the duration of the rainfall t. The run-off coefficients and the discharges, according to Korbély are stated in Tables XI and XII. Kenessey (1928) computed the annual average run-off coefficient by coefficient fractions, that is a=«i+a

2 + «3 (See Table XIII). In case of a rainfall of t hours the run-off coefficient is « = a + „ . Kenessey fixed the constants of his formula in empiric pT+i way for all of Hungary's hydraulic territories of different characteristics. The extent of the run-off coefficient is influenced by the rainfall conditions, by the peculiarities of the watershed area and finally by the weather and climatic conditions. This is why the run-off coefficients vary even on the same watershed area. In our determination, therefore, we may not generalize but the actual value must be calculated separately in each case. The determination of the run-off coefficient by actual measurements has taken place, sporadically, also in the past. This is exemplified in Tables XIV and XV. Such observations are carried on in the United States on experimental model areas (See Fig. 3). In the following the method of determination of the actual values of the run-off coefficient for the national flood control societies is introduced. In calculating we must know: A

) The quantity of water gained in form of precipitations, B) the quantity of the run-off thereform. A ) This value may be determined simply by the rainfall data. В

) The quantity of the down flow water may be determined, 1 ) with the aid of a series of discharge measurements taken during the rainfall (Fig. 4), 2) with the discharge curve, or — in case of artifical drainage — 3) by the capacity of drainage pumps. The Hydrographie Institute avails itself of the method mentioned under 2. Fig. 5 exhibits a flood wave caused by a rainfall and the calculation of an actual value of the run-off coefficient. On Fig. 6 — taking the constant water discharge of the canal to be zero or greater (alternative A or B) — we prove that the quantity of water run-off of the precipitation is shown with lines drawn vertically on the water quantity curve at the beginning and the end of the flood wave on the surrounded territory. Table XVI contains the actual values of run-off coefficient which can be established by observation on the watershed area of the Sárszentmihály gage on the Nádor canal during the outstanding flood waves between 1932 and 1941. The highest values of each month are considered to be competent. Seasonal variations are shown in Fig. 6. According to this exhibit the relative maximum appears to be in spring and the minimum in summer. The location of the extremities, the relative position to each other, further their number and quality may vary on the different watershed areas, in the first place in accordance with the climatic conditions. Table XVII and Figures 9 and 11 show our calculation results of five further gage sections. The maps of the watershed areas are to be found in Figures 8 and 10. As a general rule it may be said with respect to Hungary that the maximum of the competent run-off coefficient is in the months of February to March, or October to December, the minimum in the months of June to August. 3. Calculation of the rate of run-off. Knowing the rainfall and the run-off coefficient we may now proceed with the calculation of the rate of run-off. The rate of run-off (q) is always related to a certain watershed area, moreover even to a particular point of such watershed area. If the most critical T days rainfall is h (inches, mm) then during the time T the water quantity on the watershed area F will be hF, of which in case ot maximum run-off coefficient a, ah F water quantity drains off in all. The problem would be a simple one if for the duration of the rainfall the run-off were uniform. In this case the rate of run-off would be — . However, the run-off is not uniform and, therefore, the problem of establiT shing the compound maximum becomes complicated.