Vízügyi Közlemények, 1967 (49. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(4 3) and the weight of upper layers. Drying is accompanied by shrinkage. After repeated cycles of drying and wetting the condition of "stable density" is gradually attained, which, however is influenced to a certain degree by the prevailing moisture content. Owing to differences in the swelling properties of individual layers, zones of greatly reduced density are developed at the interface of layers. Changes in condition are caused by changes in soil structure due to ion exchange, weathering and coagulation of the clay minerals. These result in an increase of permeability, but are not necessarily accompanied by a change ot' density. Ageing can be prevented effectively by placing a hydraulic-fill supporting body of sand at the landward side of the levee. Besides adding to stability and providing free drainage to seepage water, the sand prevents - thanks to its low capillary lift excessive drying of the soil and offers thus protection against changes of condition. In order to obtain better understanding of the behaviour of levees exposed to repeated wetting and drying, the determination of colloid-state parameters, besides conventional soil-mechanical properties, is deemed desirable. Criteria governing the attainment of equilibrium conditions and mechanical properties pertaining to these should also be determined. 3. Laczay, I.: Peak stages during the i!)(>5 Danube highwater in the flood-bed ot the Upper Danube reaeli. Effect of the highwater on bed development (for the Hungarian text see pp. 119) After the passage of the 1965 Danube highwater, peak flood stages were determined at 52 points (Fig. 1 ) from highwater marks on trees in the branch system of the river, which covers a flood bed of about 22 sq.km area. Results of this survey were compared with readings on flood gages located along the levees. The average slope of the peak water level over the reach considered, in the flood bed along the right-hand bank was found to vary from 47 to 50 cm/km (Fig. 2). Across the bed the differences in water level were of the order of a few cm-s only (Fig. 3) In the vicinity of branches conveying considerable discharges the watersurface was mostly higher by some cm-s than over the surrounding flood bed area. At contractions of the latter the watersurface rose to a higher elevation at the levees as well. The contour lines of highest water levels are largely normal to the overall flood-bed. The average transverse slope within the flood bed varied from 0 to 8 cm/km. The effect of the highwater on bed development was studied by levelling lowest stages and sounding tachvgraphic surveys (Fig. 4). Fords in Autumn, 1965 were found to be generally higher than previously. The extreme highwater transported large volumes of bottom load to the reach and deposited it there. These bed-load deposits gave rise to appreciable changes in the slope conditions of the drv-weather watersurfaces as well. Special consideration was given to conditions which developed by July, 1965, around River Station 1823 km on the Danube. From reports by the Waterway Marking Service it was determined that here the bottom rose temporarily almost to the elevation of the lowest navigable stage (Fig. 5), while the new transition developed by Autumn (Fig. 6). Changes in the channel can be traced clearly on cross sections determined from survey results (Fig. 7). Changes by the deposition of loose sediment during highwater in the channel are presumably considerably greater than determined by subsequent observations. In fact, medium and low waters following highwater are capable of restoring disturbed flow conditions in a remarkably short period effectively. A. Petrasovits, /., Dr., Agric. Engr.: Irrigation on Corsica (for the Hungarian text see pp. 128) Corsica occupies a particular position in the agriculture of France. The development of agriculture there is impossible unless its intensity is enhanced. The main features of the development of irrigation are as follows: 1. Trends for the establishment of large farming units. 2. Multi-purpose investment. 3. General application of irrigation. 4. Multi-purpose waterhouseholding by storage of irrigation water. 5. Irrigation plots equipped with semi-permanent sprinkler installations.