Hidrológiai Közlöny 1971 (51. évfolyam)

1. szám - Dr. Öllős Géza: A kutak vízhozamát befolyásoló tényezők

Hidrológiai Közlöny 1971. 1. sz. 17 Factors affecting the yield of wells Dr. ÖHŐS, GÉZA Assoeiate Professor, Candidate in Technical Sciences Budapest Technical University 1. Introduction Formerly, in the early stages of development, any attempt at deseribing the yield of wells and, in generál the hydraulie properties of water producing systems was based on several simplifying assumptions: — the well—as a hydraulie system—is unaffeeted by the time of operation; its behaviour is thus unchanging, — the permeability coefficient k of the aquifer is constant, i.e. the properties and configuration of individual grain surfaces of the particles forming the soil suffer no changes in time, — the rangé of influenee pertaining to wells, is not affected by ambient factors (e.g. pollution), — the internál and external boundary conditions of seepage remain unchanged. With these simplifications the application of the potential theory became possible, resulting in an indispensable common professional language for interpreting seepage around wells and rational water production. Experience gained while operating wells, has shown the yield to decrease, besides the periodic changes related to the continental climatic conditions, quite often alsó gradually. Seepage phenomena have been reported in the literature which make the revision of existing theories and the study of the actual process of seepage necessary from the very beginning. It is essential to diseover the factors actually dominating in the process. This requirement, however, does not only arise in connection with the operation of wells, but in several other fields, too. (Thus for instance in water- and sewage treatment technology, the investigation of the process-details, the physical, chemical, biological processes, and the determination of the actual relations, became a major problem in recent times.) The yield and in generál the water quality affecting factors are treated on basis of the following papers, submitted to the Congress Committee: J. Hampl : New elements in the withdrawal of groundwater by bored wells. J. Holluta— H. Sontheimer : Improvement of the quality of surface water by bank filtration. Mrs. A. Homonnay : Studies into the factors affecting variations in the iron-rnanganese content of water obtained from the gravel terrace wells of the Budapest Municipal Water-works. S. Karácsonyi : Reduction of well yield, caused by water quality. A. Kepinski: Problems associated with the selection of protect ion areas around groundwater producing areas. K. H. Kludig : Factors affecting the volume of water potentially produced from bank filtered groundwater and the quality of water in riparian wells. 1. Kontúr : Stochastic models on the operation of bank filtered wells. V. Kulhauy: Changes in the quality of subsurface water in a vell during a pumping test and over the year. L. Marton : Recent studies on the clogging of wells P. Mauersberger : On the yield of not-fully penetrating wells. W. Mevius : The reduction of well yield. G. Ollós : Problems of aquiring water in case of bank filtration. Gy. Pusztai : Factors affecting the yield from bankfiltered wells. Os. Szolnoky: Studies into the hydraulics of well filters. The factors influencing the yield and quality of the wells can become effective in the entire influenee field of seepage pertaining to the well. Of the variety of physical, chemical and biological factors, the one which, in what measure and in which part of the seepage field is effective, can be decided first of all by a careful analysis of the boundary seepage conditions and the physical, chemical and biological influenee of material— soil, water, pollutants, etc.—contained in the seepage field. The situation may be entirely different, if the water pumped from a waterbearing formation or great depth is compared with that produced from bank zones in the vicinity of highly polluted surface water or, for instance by groundwater recharging. This example indicates clearly that the seepage directed towards the well must be regarded, in its most generál form, as a filtration process! If this assumption is valid, then the seepage in question may be regarded as a process in water treatment technology. At this point the established and accepted theory of seepage hydraulics must be extended. It is undeniable, that if this theory is combined with the already established one, "wellhydraulics" is bound to become more complex, and to receive a broader meaning. However, the fundamentals of the process are represented better, and, after all, this can be the only correct tendency. By this approach the quantitative and qualitative changes of the filtering water — be it favourable or unfavourable—can be interpreted rationally. It is my aim to discuss the 14 papers submitted in this generalized frame. 2. Processes in the close vicinity of wells, the clogging oí wells The quality of water seeping in the rangé of influenee and nearing the close vicinity of the wells, is controlled by the combination of supply conditions and the conditions in the seepage field, respectively. Thus, when assessing the operation of the weli, this state of water quality must be adopted as the starting basis. The following processes may induce the well to behave other than designed: — silting up, — corrosion in the well-structure, incrustation.