Vízügyi Közlemények, 1954 (36. évfolyam)

2. szám - XV. Szilágyi József: Az Erzsébet-híd roncsainak hatása a mederalakulásra

(51) ops, while if the drawdown is greater than the critical depth, the free drawdown curve is formed. In the latter case the water levels in the well and in the aquifer separate. Both well theories are based on Darcy's law and presuppose knowledge of permea' bility coefficient k. This coefficient is generally taken for constant, although some researchers have recently pointed out that it is not constant, but varies with the slope, or the velocity of ground water. However, they have not succeeded in establishing a law of this variation. To determine the variable coefficient of permeability the author introduces the concept of the hydraulically equivalent porosity diameter (d

e

), by the following postulate : Through unit section of a fictive aquifer built up of straight pipes of that diameter, at same head p and effective velocity v

t, the same quantity of fluid Q should percolate. This condition is satisfied if the equivalent porosity diameter is computed from Hägen-Poiseuille's formula (17). (g = gravity acceleration ; v = kinematic viscosity). For the calculation of d

e (formula 19) effective velocity v

t and hydraulic gradient i must be known. These values are determined by test pumping. With data thus obtained the relationship between effective velocity v

t and equivalent porosity diameter d

e can be graphed in a double logarithmic system in general as a straight line. (See fig. 4.) With the aid of the diagram equivalent porosity diameter d

e can be determined for any effective velocity v

t occurring in the aquifer examined, from which the coefficient of permeability is obtained by formula (24), where n is the porosity ratio of the aquifer. This procedure is not the only method for calculating the variable coefficient of permeability. It is easy to suppose that for different aquifers relations can be drawn, between apparent velocity v

s and hydraulic gradient i and in this case the coefficient of permeability is calculable for any point of the drawd ЛУП space by formula к =• Vs/i. In this case there is no need to introduce the equivalent porosity diameter. The author is of the opinion that in the investigation of theoretical problems of ground water motion, Reynolds-number R

e (21) is to be calculated with equivalent porosity diameter d

e and effective velocity v

t (Fig. 6.). Examples illustrate calculation with the variable coefficient of permeability. Computations hitherto made show that for Dupuit's formula (7) the permeabJity coefficient determined near the well has to be applied (Table III.). In Table IV some points of the drawdown curve observed at one test pumping (Fig. 3.) were computed. Start was made from observed point x = 0,55, у — 6,41 m ; by stepwise calculation according to formula (11) point y = H was reached and thereby the radius of the circle of influence R = 170 m was determined. At x = 5 m and at a; = 15 m, there are discrepancies of +2 cm and +3 cm respectively, between observed and calculated values. In Table V the section of the drawdown curve for another aquifer was calculated between the point of observation x = 2,5 m and the test well. At the border of the gravel screen (x = 0,6 m), the angle of inc ination of the drawdown curve is tf = 57°24'. therefore this is a case of backed up drawdown curve. In Table VI in the same aquifer the maximum discharge and the pertaining critical drawdown from the piezometric surface were calculated by iteration and interpolation. The examples demonstrated present^ the application of the variable permeability coefficient calculated with the equivalent porosity diameter. ИЗМЕРЕНИЕ РАСХОДА ВОДЫ У ВХОДА ВСАЫВАЮЩЕЙ ТРУБЫ. Фаи Ч. (Рисунки см. на 330—344. стр. венгерского текста) ОДТ. 532.574.5 В статье даются итоги опытов измерения расходов воды у входа всасывающей трубы, предлагаемых для решения задачи измерения расходов осушительных и оросительных насосных станций. Статья разделена на три главы : в первой излагаются теоретические зависимости •служащие основой измерения, в второй занимается автор способами измерения, типами приборов и их изготовлением. Третья глава описывает установку прибора, помещенного добавочно для измерения расхода уже раньше построенной осушительной насосной станции и дается изложение проведения тарирования прибора, а потом резюмируются результаты измерения. Более подробное резюме дается на французском языке. v4*