Vízügyi Közlemények, 1971 (53. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(42) — changes in the channel, i.e., scours and silting in the vicinity of the structure (Fig. 10), — the dynamic pressures arising in the course of operation, such as wave action, surge waves, etc., (Fig. 11 ), — the changes in the temperature of seeping water, — the escape of air, — groundwater lowering during the period of construction. In estimating the uplift force, it is thus necessary to include factors increasing and reducing it. The relevant methods are described. The computations performed accordingly revealed 10 to 20% changes in the uplift force at a low head weir (with a differential head of 7 m under normal operating conditions). 3. Varga, D., Civ. Engr. : The attenuation of flood waves in the Merenye Reservoir (For the Hungarian text see. pp. 225) The Merenye Reservoir is situated in the south-eastern hilly part of Hungary ( Fig. 1 ), on the main branch of the Gyöngyös Creek. The area of the watersurface is 122 hectares and the reservoir may be regarded as representative of small ponds as far as flood retention is concerned. 43 mm rainfall on the 9th August, 1970 was followed by a 52 mm storm on the 10th and additional precipitation on subsequent days. This resulted in a flood wavre of 200 hours duration, the peak of which reached the reservoir on the 11th already and caused a head of 117 cm over the spillway crest. Observations and measurements have been performed during the flood, which made the construction of the diagram of Fig. 2 possible. The passage of the flood wave, the changes in storage volume, the hydrograph of stages and overflow are illustrated therein in a highly visual manner. The relationship between the curves is illustrated by the example showing representative stages, discharges and storage volume in the 100th hour of the flood wave. A check on the method is offered by the fact that the points 8 and 2 lie on the same horizontal (at 4.2 cu-m/sec). The good agreement in the example may be regarded as a verification of the reliability of the visual method. The attenuating effect is reflected by the 0.43-fold reduction of the peak discharge and by the fact that the maximum volume stored was 0.34 times the total water volume conveyed by the flood wave. The probability of occurrence of the peak discharge is estimated at 3%. To illustrate the flood the upstream and downstream sides are shown in Figs. 3 and 4, respectively. Under the influence of the reservoir the discharge over the downstream sections was considerably reduced, which proved especially beneficial for the highways.