Vízügyi Közlemények, 1960 (42. évfolyam)

4. füzet - VI. Képek a Föld különböző részeinek vízépítési munkáiról

(12) appears as the resistance of the filter tube itself (Fie/. 1). If, however, the filter tube is surrounded by soil, the filter-tube resistance \h

2) is complemented by the soil resistance (ftj) which is due to characteristics of the thx-eedimensional groundwater movement (Figs. 3a and 2b). For computing this latter resistance the original equation of Ehrenberger has been modified by the author as i. e. the influence of the well radius on the vertical departure of water levels within (hb) and outside of the well (Л;

г) has been allowed for [Eq. (1)]. If there is a gravel filter between the filter tube of the well and the soil, the resistance of the gravel filter h

3 is added to the former two resistances (Fig. 3). The well being positioned in the water yielding soil layer and exposed continually to the harmful effects of chemical action by water, the provision of appropriate observing wells (Fig. 4) besides water metering is also necessary, to thus obtain a continuous and reliable record about the „life" of the well. The theoretical determination of filtertnbe resistance is associated with the names of S. J. Peterson, C. Rohwer and L. M. Albertson (Eq. 6). The theoretically possible lowest value of filtertube resistance can be derived therefrom (Eq. 2). The theory permits conclusions to be drawn as regards the economical length of the filter tube. The magnitude of filter-tube resistance is appreciably influenced by the quantity of filter apertures. The effect resulting from increasing the aperture-area of the filter tube can to a certain extent be attained essentially also by increasing the contraction coefficient (C

x) of the apertures. Apertures may be considered as of favourable shape, if the outer edge of the apertures or holes is sharp and, starting from the external surface of the mantle, the cross sectional area thereof increases. Favourable hydraulic conditions can most successfully be created by narrow and long apertures. However, besides hydraulic considerations other aspects should also be allowed for in selecting aperture cross sections. The development in time of corrosion and clogging depend greatly on the shape of the cross section, i. e. the shape characteristic. In other words a most favourable shape will be defined by these aspects as well, and the latter will not necessarily be identical with the best shape determined on the basis of hydraulic considerations. Following Boss (Fig. 7), and later У. Vaadia and V. H. Scott the modification in filter resistance under the influence of the gravel filter (Eq. 7) is also dealt with (Figs. 8a-d). The choice of material for the gravel filter and its coordination with the geometry of the filter apertures has been found to require careful attention. Experimental investigations are being conducted in this direction at the I. Institute for Hydraulics of the Technical University for Building and Communication, Budapest, with the aim to clear further — hitherto unsolved — hydraulic problems of well filters. Chemical effects of water are of fundamental significance for the design and operation of well filters. The reduction of well yield, — the ageing of wells — may be traced back to a) clogging, b) corrosion. Developments in the design of well filters have revealed that the process of clogging should be subject to increased research work in the future, inasmuch as the ever spreading use of nonmetallic filter materials can be expected to minimize the problem of filter corrosion. As revealed by investigations both at home and by Ch. Truelsen into the phenomenon of clogging, a close relationship exists between separations of time and ferro-compounds related to the laminar or turbulent nature of seepage flow around the well. Thus the proper choice of the well diameter also affects the development of velocity conditions around the well. A review of well filters currently used as well as trends of development is given in Part II of the paper. As regards well filters with filter fabrics, it can be established, that from among all kinds of well filters these are subject to most adverse effects. The tendency is ta 3