Concerning the Degree of Accuracy of the Gibson Method of Measuring the Flow of Water

Abstract

Abstract The paper first discusses the limitations of various methods of measuring water which were in use when the Gibson method was first announced. These limitations of the current-meter method of flow measurement include: The effect of turbulent accessory motions which cause periodic velocity changes in the direction and magnitude of flow; the difficulty in obtaining readings close to the wall of the canal or closed conduit; and the necessity of determining the velocity at several points simultaneously due to temporary changes in distribution; and the expense involved in taking a number of such simultaneous readings. Reference is also made to the use of the pitot tube for taking readings close to the wall of the passage. The greater part of the paper, devoted to a discussion of the Gibson method of water measurement, includes the derivation of formulas involved in this method of water measurement, its limits of accuracy, and the errors which may arise in its use. These errors, due to (a) accessory motions, (b) to false valuation of friction, (c) to friction of the mercury column, and (d) to inertia of the mercury column, are presented with derived formulas and approximate values together with suggestions for minimizing them.