Vízügyi Közlemények, 1973 (55. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(41) irrigation projects is shown in Fig. 9, of which the projects Novo-Selo, BelmekenSistrimo, Aleko-Potoka, Topolinitsa and Tinkovo-Peroy are illustrated in Figs. 10 to 15, respectively. In Chapter 6 detailed data are given on three typical irrigation projects, namely the Beli-Lom, the Novo-Selo and the Tinkovo-Peroy projects. In each of them the schedule of operation is determined using the method of A. M. Alpatiyev, which is founded on the periodic measurement of soil moisture. The majority of sprinkler irrigation systems features a mixed network, with the laterals being shifted manually. Surface irrigation is also practiced with low-pressure pipelines and portable plastic pipes. Automatic control (tailwater regulation) of the projects has been introduced recently. The automatic hydrants of completely permanenet projects are controlled from the pumping stations. Chapter 7 is devoted to the problems associated with designing, construction and operation. In Chapter 8 the considerations governing the future development of irrigation farming are outlined. It is envisaged to organise farming operations into agriculturalindustrial plants with areas ranging from 20 to 50 thousand hectares. The capacity of existing surface irrigations will be enhanced by extensive reconstruction and lowpressure irrigation hoses will also be introduced ( Figs. 17 and 18). Systems with portable, mixed pipelines will be retained for sprinkler irrigation, while for vegetables and perennial crops completely permanent installations will be used. PROBLEMS RELATED TO THE STRENGTHENING OF FLOOD LEVEES By Jolánkay, Gyula, Civ. Engr. (For the Hungarian text see pp. 215) The factors affecting the degree of protection offered by flood levees are evaluated. The former definition of the concept of "safety freeboard" is subjected to detailed critical analysis and reevaluated in the interest of enhanced safety. For strengthening of the levees a "mixed type" profile is suggested in order to create levees of equal safety along their entire length, capable of guaranteeing a higher degree of safety. The paper consists of two parts. Part I deals with the factors influencing the protective capacity of flood levees and examines in detail the causes of levee ruptures experienced in Hungary (Table I). These causes are summarized and discussed as a) rodent holes, b) overtopping, c) seepage in layers, at the foundation interface and consequent slumping of the air-side levee, d) wave action and e) foundation failures. Of these the safety freeboard, i.e., the height of levee above the design flood stage, is discussed under b). In Part 2 a few "mixed type" cross-sections arc suggested lor the strengthening of levees at the present with an experimental character. The "mixed type" strengthening section shown under a) serves to provide protection against wave action and to raise the levee crest, while that under b) to raise the crest and to strengthen the levee. The main conslusions and the recommendations of the paper are given below: 1. In view of the as yet rather frequent cases of levee overtopping, the variable freeboard along the levees, further of the growing population and value of property in the flood plains, the rising of levee crests is an important task of the present and will remain one in the future as well. For this reason typical cross-sections are needed which permit rapid construction work, repeated raising of the crest and afford still a cheap solution. 2. One of the weaknesses of the main flood levees, the length of which exceeds 4,000 km, is that seepage in them gives rise to detrimental phenomena in a great number of places. Thin impervious cutoff walls penetrating the levee body and extending 1 to 1.5 m deep into the original subsoil, further resisting burrowing animals may offer a remedy Lo this weakness.