Hidrológiai Közlöny 1967 (47. évfolyam)
10. szám - Dr. Kovács György: A szivárgók környezetében kialakuló nem permanens vízmozgás jellemzőinek gyakorlati meghatározása
442 Hidrológiai Közlöny 1967. 10. sz. Kovács Gy.: Nem permanens vízmozgás kennzeiehnen genau das geschilderte Strömilngssystem und als Náherung kann dies auch im Falle einer Freispiegel-Bewegung verwendet werden. Im wesentlichen ist diese Annahme namlich mit der auch bei der Linearisierung angewandten Annaherung identisch. Berücksichtigt man weiters jene Vereinfachung, laut der sich die Bewegung vom Ort des Eingriffs bis ins Unendliehe fortpflanzt und die Wirkung vom ersten Moment an an der ganzen Strecke auftritt, dann erhalt man Beziehungen zur Bereehnung der infolge absenkender Wirkung eines Gerinnes oder Sickergrabens entstehenden nichtpremanenten Wasserbewegung. Die Gleichungen können — mit Berücksichtigung der Richtung der Veránderung — natürlieh auch dann verwendet werden, wenn wir nicht die AbSenkung, sondern den Grundwasserandrang der Linie entlang charakterisieren wollen. Nach allgemeiner Ableitung der Beziehungen (Gleichungen 7—14) schreiben wir, entsprechend den im Sickergraben zustandegebrachten verschiedenen Grenzbedingungen, die Gleichungen auf, die zur Bereehnung der im Ausgangsprofil zustandekommenden zeitlichen Veránderung (s 0), der in den Sickergraben von einer Seite in Streifen von Einheitsbreite einströmenden Abflussmenge (Q 0), weiters der zeitlich und örtlich veranderlichen GrundwasBerspiegel kennzeichnenden Absenkung (s/x;t) dienen. Die untersuchten Grenzbedingungen sind folgende: a) Absenkung mit konstantem Niveau (Gleichung 19 und 20, Abb. 2); b) Entnahme konstanter Abflussmengen (Gleichung 25 und 26, Abb. 3); c) Einer bestimmten maximalen Absenkung stufenweise zustrebende Depression (Gleichung 35, 36 und 37, Abb. 4); d) Untersuchung eines ununterbrochenen Betriebs aus Abschnitten mit konstanter Abflussmenge und Absenkung (Gleichung 42 und 43, Abb. 5). Die Zusammenhiinge sind einfach und ermöglichen die Lösung der in der Praxis vorkommenden wichtigsten Angaben. Mit ihrer Anwendung können wir nun die bisher oft angewandte Lösung ausschalten laut der wir als Annaherung auch die Kennwerte der nichtpermanenten Sickerung aus den für die permanente Bewegung abgeleiteten Gleichungen bestimmt habén. Practical Detcrmination of iho l'arameters Describing Non-Steady Flow in the Vicinity of Drains By Dr. Kovács, Gy. Doctor of teclin. Sc. In cases where water is removed from the groundwater the surface of which is under atmospheric pressure, or water is added thereto, the effeet of this interferenee will proceed gradually and results either in a diminution, or an increase of storage within the layer. Seepage flow of this type should therefore be taken into consideration aS non-steady movement in calculations. The common basis of every approach towards a mathematical deseription of non-steady movement is the equation of continuity, in which the variatior. of discharge in the direction of flow is equated to the ehange of storage which occurs in time. When this is combined with the dynamic equation of free-surface flow — written by taking Darcy's law into consideration — the differential equation of Boussinesqu is obtained. This basic equation was of an order higher than unity and several attempts have been made in earlier methods to make this differential equation a linear one. Different solutions have adopted a basically similar approach for this ]>urpose. In describing horizontal flow the variable depth is replaced by a mean depth determined in a certain manner and variations in depth with time are alsó meglected. Since this simplified approach is substituted into the originál basic equation, a highly eomplex expression is eventually obtained, which found no wider application in practice and in which the physical significance of the simplifying assumptions has becoine obscui-ed. Considerations may however be extended to the seepage field occurring in nature, which is exactly deseribed by the simplifying assumption outlined above and introduced in the interest of obtaining a linear expression. The basic equation is determined aceordingly by combining the dynamic equation for flow under pressure with the equation of continuity and the resulting expression may be solved directly without transforming it into a linear one. The seepage field is deseribed exactly by the solution obtained which may be applied to approximate free-surface seepage conditions as well. In fact this assumption is essentially identical to the simplifieation introduced for making the equation linear. Introdueing further the simplifieation that movement extends from the point of interference to infinity and that the influence is felt from the first instance over the entire section, expressions are suggested for calculating the non-steady flow caused under the influence of the drawdown created by a canal, or drain. With due regard to the direction of cliange, the expressions can be applied, naturally, alsó to the case where instead of drawdown, recharge to groundwater along a straight line is contemplated. After the generál development of relationships — Eqs. (7) to (14) — equations are written in accordance with boundary conditions created in the drain for caleulating variations of drawdown in the initial section with time (s 0), the discharge Q 0 entering laterally into the drain through unit length, as well as the drawdown characteristic for the variations with time of the groundwater surface (s/x; t). The boundary conditions taken into consideration are as follows: a) drawdown to constant level — Eqs. (19) and (20), Fig. 2; b) withdrawal of a constant discharge — Eqs. (25) and (26), Fig. 3; c) depression tending gradually to a specified maximum drawdown — Eqs. (35), (36) and (37), Fig. 4; d) continuous operation consisting of periods of constant rate of withdrawal and of sueh to constant drawdown level — Eqs. (42) and (43), Fig. 5. The relationships given are simple to handlé and offer opportunity for solving the most important problems encountered in practice. The approach frequently recurred to so far and consisting of the use of equations developed for steady movement for the approximating determination of parameters of non-steady flow, can be avoided by the application of the formuláé suggested.
