Vízügyi Közlemények, 1962 (44. évfolyam)

4. füzet - IX. Könyvismertetés

(35)* Nemecek, Eq. (3), appears for the time being as the most suitable for calculating the radius of this filter. Relying on his investigations an explanation is given bv the author for the role of the cylindrical filter with reference to Fig. 14. Accordingly, if there is no filter around the horizontal well section, a vertical drop ensues between the water levels at the external and internal sides of the shaft, as a result of the small seepage cross section around the horizontal section. The fact that drop is usually small in practice is due to the very existence of the cylindrical filter. From among the numerous beneficial effects of the cylindrical filter its contribution to a higher yield should especially be" noted. Reviewing the characteristic hydraulic parameters it will be perceived that the hydraulics of vertical filter wells is described by the parameters in Eq. (4), whereas that of horizontal filter wells by those in Eq. (5). The increased number of factors in the latter is alone an explanation for the lag in the theoretical development relative to the practical design. Considering the fundamental hydraulic problems relating to the horizontal sections, a detailed analysis is given with reference to Fig. 19, of the velocity v' of water entering into the horizontal section along its length, and of the velocity v" of water moving parallel to its axis. The analysis is performed for different hydraulic conditions. From this figure, as well as from a closer inspection of recharge conditions, it will be perceived, that the hydraulic conditions differ for various horizontal sections of a horizontal filter well. Thus the yield of individual horizontal sections is greatly influenced for instance by the method of recharge, i.e., whether it occurs from the groundwater, from all directions towards the well (Fig. 18), from a principal direction only (Fig. 21), or from the bed of an open watercourse (Figs. 26 and 28). Studying the factors affecting the optimum length of a horizontal section it is definitely pointed out that the hydraulic boundary conditions play an especially important role in this respect. With this approach the optimum length of the horizontal section in Fig. 24 appears to be about 30 m. If the horizontal section is left unperforated over a length adjoining the shaft, the main difference relative to the seepage flow pattern pertaining to a full length perforation is (Fig. 18) that closed, three-dimensional potenciál surfaces (Fig. 25) develop around the perforated section. The effect of these closed potential surfaces should be investigated in detail. When trying to find the optimum length of a horizontal section extending to under the bed of an open watercourse, it will be found that increasing them beyond a certain limit will bring no additional benefits, since water will always follow the path of least resistance. As a consequence of this water from a certain part of the bed can only reach a section extending to under the bed (Fig. 30 ). The influence surfaces thus developing and pertaining to the individual horizontal sections may join each other in a highly complex manner. The yield of the horizontals is thus seen to depend on a variety of factors. The mutual influence of the horizontal sections on each other, respectively the yield of the well, is dealt with in Section 10. In this connection, on the strength of laboratory investigations, the yield of a horizontal section (Fig. 33) under various hydraulic conditions (e.g. Figs. 26 and 28) is demonstrated also in a quantitative manner. As revealed by the detailed analysis, the most advantageous conditions for the yield of a section, respectively of a well, ensue during the operation of wells located in the bed, and those supplied by groundwater recharge. In conclusion it is established that the development of a wide variety of horizontal filter wells is primarily of economical interest. As far as the well yield is concerned, the arrangement in space of the horizontal sections should as closely as possible be adjusted to conditions of supply to the well. The extension of the influence radius of the well, the most favourable flow of water to the filter surfaces, and a reduced interference between the individual horizontals can be accomplished thereby. However, it is remembered at the same time that great care should be taken to maintain proper conditions of supply to the well. (Translated by Z. Szilvássy struct, eng.)