Hidrológiai Közlöny 1947 (27. évfolyam)

1-4. szám - TUDOMÁNYOS INTÉZETEINK KUTATÓ MUNKÁJA

XXVII. évi. 19/,7. 1—!,. szám. HIDROLÓGIAI KÖZLÖNY 37 gravels, mica (muscovite and biotite), grains of magnetite, pyroxene, amphibole and g a r n e t. Grain analvsis sample taken on 3-rd July 1941 (Fig.2). The Szent János-Spring has a mud of similar colour and similar size of grain to that of§ the Szent AntalSpring. Baryte was not found in it. In addition to calcite and a r a g o n i t e, a considerable amount of p y r i t e, quartz from Danube gravel („pink quartz"), pyroxene, amphibole, mica and g a r n e t, make up this mud. Grain analysis sample taken on 3-rd July 1941 (Fig. 3). The Török- and Zug-Springs of the Császár-Bath havequite different characteristics from the above-named. They are lukewarm springs, consequently there is no aragonite in the mud. Their colour is yellow. Crystals of calcite are separated from them. Quartz, pyroxene, amphibole, garnet and mica form deposits. The composition of the mud according to size of grain is shown. (Figs. 4 and 5. Sample of Török-Spring taken on 3-rd July 1941 and the sample of Zug-Spring on 17-th July 1941.) The muds of the two last springs, i. e. the MáriaSpring' and the Nádor-Spring, are the same, like that of the Szent Antal- and Szent János-Springs. Baryte was not found in them. It is specially interesting in NádorSpring, that its a r a g o n i t e forms granules of poppyseed size. Grain analysis samples taken on 17-th July 1941 (Figs. 6 and 7). I have preserved microscopical preparations of the more interesting minerals. This work has been made in the Mineral and Geological Institute of the' Hungárián Palatin Joseph University of Engineering and Economic Sciences. M ICV FLOODS. By W. LÁSZLÖFFY, D. Eng. (Hungárián text with figs. on p. 9.) D. C. 627.51:551.482.215.3 On the hasis of the flood records eoncerning the Danube for nine centuries and of extensive hydrographic observations which were started in the year 1818, the following generál rules may ba established with respect to the ice conditions of the rivers and iey floods. 1. (At the time of the farming of ice the cooling fragments of water crystalize around silt particles (vvithin the cross section or on the bottomi. On river sections with great slopes the cooling off is slower that on sections with smaller slopes, therefore the forming of ice is slower. Dining the winter season, the water becomes clearer and clearer, and so the forming of ice — at the same temperature — is slowed down. 2. The rules of drifting ice were expressed by Schoklitsch with the formula. 1.) In this formula the width of the water surface is represented by B. the mean surface velocity by V, and the rate of ice cover by n (n 1) in cross section 1 and 2 following each other. In harmony with the formula the rate of ice covering will increase in accordance with the decrease ol the velocity (lessening of the slope) as well as by the decrease of the width (narrowing of the river bsd, ebbing). As the slope of rivers decreases towards their mouth the rate of ice covering will increase on the way down the river. 8. Freezing in. Ice floes stopped in sharp meanders and wadings (figs. 2 and 3) may suddenly increase the ratlo of ice-covering: and, n will be 1, the surface will become covered by solid ice. In using the definition of Prcfessor Cholnoky (Budapest) these are the so called middle- and lower- course river sections. (Über Flusstaler. Mitt. d. Geogr. Ges., Bd 70, Heft 1 3, Seite 43, Wien 1927. Published in Hungárián first in 1925). In the following time the water moves in a rough pipe under pressure, and therefore the stage rrses suddenly (fig. 4). But sutsequently, after the surface of the ice wears off, and in consequence of the decrease of the discharge the stage will fali resulting in tying of the ice cover to the banks. The ice cover will be stronger, 1.) the colder the winter is; 2.) the more the stage decreases after the freezing of the water; 3.) the less the velocity of the water (wearing off); Jf.) the less the slope is (i. e. the sooner the river has frozen in). The resistance of the riverbed will increase 1.) the lower the stage of the river was at the time of freezing in (narrow cross-section); and 2.) in accordance with the heaviness of the ice barrier (sudden freezing, subsequent sliding). From the point of view of geographical situation the lower sections of the river with the lesser slope is in a rather disadvantageous position, while from the point of view of climatic conditions the worst is a rigid winter following a dry autumn. 4. Ice dritt. The solid ice armour melts slowly in contrast with the snow cover of the sloping land. The cross section below the ice is narrow, the pressure of rising water, will therefore break open the ice cover aownward. Meanwhile in the river meanders, narrow3, etc. ice barriers will form. The ice will clog up the flow of the water (fig. 5) and the water will rise until it pushes the obstacle out of its way, or will detour sideways across the river banks. The ice cover disappears not in the upstream direction but generally dowmvards resenibling a carpet being rolled up. The moving off of the ice is more dangerous, 1.) the lower the stage of the river was at the time of freezing (narrow riverbed); 2.) the heavier the ice is; 3.) the more vehement the flood is; 1,.) the less the slope of the river; 5.) the less deep the riverbed is cut in (fig. 7) and 6.) the more irregular the riverbed is. The breaking up of the ice cover takes place in sections starting downward from the mounts of the larger tributaries. The greater the distance in which tributaries jóin the main river, the greater ice ma.sscs will accumulate, and therefore the greater the hazards of forming of ice barriers especially in the sections immediately preceding the mouth of the tributaries. The generál rules are illustrated by the exemple of the Danube (fig. 6).The section of the MiddleDanube from the mouth of the Vag to the Drava (400 km.) and the Lower-Danube (1.000 km.) are in a dangerous situation on account of the small slope. Although the latter section is considerably longer, neverthless the Middle-Danube is in a more severe state since in this section the river bed is smaller, and as there are no large unprotected lands like those along the Lower-Danube. The flood hazards of Budapest can be diminished by radical measures to facilitate the run off of the ice improving the river beds only. This must, of course, extend all the way down to the mouth ol' the Drava. Only local improvements would be of little avail. The flood hazards recurring in the recent years were due to the fact that we pass through a series of cold winters. The author has found already in 1940, •— in establishing the average temperatures of the