Vízügyi Közlemények, 1967 (49. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(4 3) RECONSTRUCTION OF FLOOD LEVEES ALONG THE YOUGOSLAV SECTION OF THE DANUBE RIVER By K. Cahun, Civ. Engr. Novi-Sad, Yougoslavie (For the Hungarian text see pp. 182) Danube flood levees in the Autonomous District Vajdaság, Yougoslavia fail to ensure in their present condition the degree of safety which would be in proportion with the property protected by them. For this reason reconstruction became necessary. The principal consideration in the design of the new levee cross sections was to prevent unwanted seepage and leakage. Accordingly the levees were designed with a watertight core and watertight lining on the waterside and a filter (drain) part on the landside. Potential leakage paths in the foundation of the levee must also be blocked. These are due primarily to forested strips along the levees. Leakage in the subsoil can be prevented either by an impervious cutoff wall, or a curtain wall. The Danube levees have been designed with the following cross sectional dimensions : crown width 6.0 m, riverside slope 1 : 3, landward slope 1 : 5 to 1:7, freeboard above design flood level 1,2 m. The great base width is very advantageous in reducing pressure gradients. The landward part is constructed of sand, in which no rodents and moles burrow passages and thus no leakage is likely to develop. The pervious landward side of the embankment body affects beneficially also the shape of the phreatic line, which emerges then at the landward toe of the levee. In the construction, respectively reconstruction, of similar levees considerable advantages accrue from the use of hydraulic dredges. Over long reaches of the Yougoslavian section of the Danube suitable amounts of impervious material, which could be used for the construction of levees by land equipment are hard to find. According to experience gained with floating dredges so far, construction costs can be cut by half, or even more over those with land equipment. EFFICIENCY OF IRRIGATION WATER By B. Sulyok-Schulek and E. Bácsi, Civ. Engrs. (For the Hungarian text see pp. 130) In practice the efficiency of e.g. sprinkler irrigation is expressed either by a constant number, or by one related to precipitation ( Fig. 1 ). This method is acceptable in the growing season, but in other times it is impermissible. Evaporation losses from irrigation water are composed of two parts, the first of which occurs in the air between commencement of irrigation and that of infiltration, the second in the soil up to the time when water is absorbed by the plant roots. The part remaining after evaporation is the useful moisture of the soil. Evaporation losses depend on air temperature, wind velocity, atmospheric humidity and sunshine duration. With a certain degree of approximation evaporation may be considered as a function of air temperature alone. In observations by the authors the evaporation loss from precipitation was found to be 75% in July and zero in January at the center of the Great Hungarian Plains. The two extreme efficiency figures of precipitation are thus 0.25 and 1.00, respectively. The efficiency of sprinkler irrigation was 0.13, that of furrow irrigation 0.15, while that of flooding 0.18 in mid July. In January all efficiencies were uniformly 1.00. For intermediate months estimates based on air temperature are possible. The accuracy attainable by this method of calculation is satisfactory for designing purposes. Soil moisture is accordingly the product of precipitation, or irrigation and efficiency. The practical application of this method is illustrated by numerical examples. The cost of irrigation is indicated in Fig. 4 and Table V for the case where the irrigation water volume, commonly applied in summer, is divided in the ratio 1.6 : 1 n*