Vízügyi Közlemények, 1971 (53. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(39) THE MAIN CHARACTERISTICS OF LAKÉ VELENCE By Sándor Bárányi, Civ. Engr. (For the Hungárián text see pp. 125) Laké Velence, with a surlace area of round 25 sq.km, is situated 40 km soutliwest of Budapest, in Transdanuvia forming the western part of Hungary. Prompted by the measures contemplated for improving the water balance of the laké, it was considered desirable to survey the bed and to determine its main eharacteristics. For the geodetical survey a network of 27 shore benchmarks was established and deptlis were determined in 14 observation profiles spaced 800 to 900 m apart from the ice cover of the overfrozen lake. To obtain information on the composition of the bottom material samples were taken at 14 points. The depth contours are shown in Fig. 2, while the thickness of the silt layer in Fig. 3. Somé of the typical bottom profiles are shown in Fig. 4. The main eharacteristics of the bottom have been compiled in Table I and Fig. 5. The area of the lake at the regulation water level is 25, 18 sq.km, of which 59% are covered by reeds. The composition and granulometric distribution of the bottom material are indicated in Table III and Fig. 6, respectively. Changes in the lake can be estimated by a comparison with the data of the survey performed in 1932 (Fig. 1). The area covered by reeds has been found to have increased by 4 sq.km during 37 years (from 38.2 to 59 sq.km!). The increase is especially conspicuous in the middle of the lake, where the expansion of the reeds may be regarded as an indication of ageing. The objective of the regulation measures is to check this process. ECONOMIC ANALYSIS OF MECHANISED EARTHWORIC IN HYDRAULIC ENGINEERING By Carlo Cahun, Civ. Engr. (Yougoslavia, Novi-Sad) (For the Hungárián text see pp. 159) Relying on experiences gained during earthwork in hydraulic engineering carried out since 1957 in the Vojvodina Autonomous Territory, earth construction by meclianical equipment is analysed with the objective of reviewing the economic aspects of such work. The structures involved were major embankment jobs and canal constructions. The former included the improvement and reconstruction of the levees after the great floods in 1956 and 1965 on the Danube, while the latter involved the construction of the large navigation and reclamation canals of the Danube—Tisza—Danube water system. Empirical coefficients and cost figures related to transportation distance are shown for both land-based and floating equipment, which are then used to analyse different techniques of levee- and canal construction work. The empirical coefficients of earth-moving equipment controlling the basic capacity of individual machines and, in turn, the unit costs of production are analysed in Section 1. The machines involved are a) the 1 cu.m dragline, b) the bulldózer, c) the seraper, d) the suction dredge and e) the transporter-dredge. Relying on the capacity and cost data of individual machines the work of levee- and canal construction is analysed in the subsequent two sections. In Section 2 levee construction work is classified into three groups, namely a) n ew levees of cohesive material, b) reinforcement of existing levees with free-draining material on the protected side and c) new levees with combined cross-section, using cohesive and free-draining materials. The cross-section of the latter —consisting of an impervious part made of cohesive soil on the waterside and a pervious supporting part made of sand, or sandy gravel on the protected side—is illustrated in Fig. 4. The unit costs of all three types of levee are shown in Fig. 5, in terms of