The estimation of discharge in unsteady flow conditions, showing a characteristic loop form

Abstract

Many methods have been used to estimate mean discharge from a river. However, the applications of such methods are inevitably affected by limitations in human resources, excessive cost, and the time required for their correct implementation, etc. Therefore, a stage–discharge curve, based on discharge and stage data measured during the normal season, has been constructed; and using this, unobserved discharge data may be obtained. The data produced by this method correspond well to measured data in a uniform flow state; however, show limitations of accuracy during variable flow conditions, such as those which may be observed during a flood season. On the other hand, the estimation of river discharge from a mean velocity equation is very convenient and rational. Nevertheless, uniform equations which calculate mean velocity in a river, such as those of Chezy and Manning as uniform equations, are not entirely satisfactory. In the present paper, accordingly, the mean velocity in unsteady flow conditions, which displays a loop form, was estimated using a new mean velocity formula derived from Chiu’s 2-D velocity theory. The results showed that the proposed method was more accurate in estimating discharge, when compared with conventional formulae. If application of Information and Communication Technology based on GPS to river discharge studies is realized, it will be possible to estimate discharge in real time.