Vízügyi Közlemények, 1956 (38. évfolyam)

2. füzet - VII. Kisebb közlemények

(613) Simplified methods of discharge measurement with current meter Discharges of rough-graded Bulgarian rivers vary rapidly, therefore discharge measurements are to be executed as quickly as possible. The following has been established 011 the one-, two- and three-point methods: 1 The relation of the velocity measured at 0,3 H (

H = depth) to the mean velocity of the vertical is fluctuating less than that of the velocity measured at 0,6 H. 2. Instead of the two-point method reckoning with velocities measured at 0,2 H and 0,8 II, at high flow calculation from velocities measured at the surface and at 0,3 II 011 the basis of the relationship deduced bv the author is more expedient. 3. The 3-point method is not commendable. From the discussion of papers during the second half of the session the following is pointed out. In connection with design flood stages Prof. C. Mateescu told that in Romania maximum water stage records dating back to almost 100 years ago on the Danube are taken for design stages, for smaller streams results computed by methods of mathematical statistics are checked by the unit hydrograph method. Prof. li. A. Marchinkov

, (Bulgaria) suggested Lhe extension of undependable statistical parameters computed from short series of discharge records on the basis оГ meteorological data. The problem of flood damage statistics was also raised. The determination of the design flood stage is mostly an economical problem, lhe basis of economic examination is the flood damage, for which an assessment method has to be elaborated. Academician E Mosonyi

, referred to the necessity of considering changes in hydrological conditions occasioned by hydraulic power stations. Finally ,S. Ilorvdth recommended lhe combined consideration of lhe stage and duration of flood waves. Prof. O. Dub (Czechoslovakia) first commented on forecasting and pointed out difficulties met on trained (canalized) rivers. On the latter forecasting is based on discharges computed from power supplied by hydraulic stations. Dr. techn. W. Kresser (Austria) described the telesignaling stage registration instrument of Linz and some interesting cases of flood and low-flow forecasts planned thereon. For speedy mobilization of great flood prevention organization forces lhe issue of approximate flood warnings

, preliminary to the forecasts proper, was suggested by some, others urged the examination of the possibility of Danube flood forecasts from precipitation data. Dr. Ing. К. Vogt (German Democratic Republic) dealt with error sources and error limits of forecasts. Collection of date 011 breaker effect endangering levees and forecasting of wind conditions was suggested. In connection with simplified methods of flow velocity measurement it was pointed out that at violent changes in discharge they may yield better results than the so-called precise but lengthy method ; on the other hand, it was pointed out that they are fit for checking point measurement results. IV. lIydrolo;|ical problems of water control Of four papers read at the fourth session the first was read by University Lecturer P. Salamin on Surface Waters from Snowmelt Calculation of daily snowmelt from the heat and from the water equilibrium equation and by combination of the two methods. The quantity of snow melt multiplied by the properly selected run-off coefficient gives the amount of surface water to be drained. By suitable elaboration of statistical data the amounts of water occuring with variable frequency to be drained from the given drainage basin during the melting periods of various duration сан be determined. (Pull text, German and French summaries of lhe paper are published in this volume.) The next paper was that of B. Weimann on Some Ilydrometrical Problems of Small Rivers Difficulties of the statistical accounting for daily discharges ; measuring instruments used in Hungarian hydrometric practice for measuring low velocities and low discharges. (Full text, German and Russian summaries are published in this volume.) The third paper was read by B. Csermák on : Computation of Flood Discharges on Small Rivers Determination of flood discharges (Q) of rivers with a drainage area of F SE S 1500 km

2 is treated. A map drawn for the assumption of the multiplicator В of the simple approximate formula of Q = Il\'F, moreover, formulae are suggested for the