Author(s): Marian Muste; Kyutae Lee
Linked Author(s): Marian Muste
Keywords: Stage-discharge rating curves; Index-velocity rating curves; Hysteresis; Hydrometry; River discharge
Abstract: Ratings curves are conventional means to continuously provide estimates of discharges in rivers. Among the most-often adopted assumptions in building these curves are the steady and uniform flow conditions for the open-channel flow that in turn provide a one-to-one relationships between the variables involved in discharge estimation. The steady flow assumption is not applicable during propagation of storm-generated waves hence the question on the validity of the steady rating curves during unsteady flow is of both scientific and practical interest. Scarce experimental evidence and analytical inferences substantiate that during unsteady flows the relationship between some of the variables is not unique leading to looped rating curves (also labeled hysteresis). Currently, the literature does not offer criteria for a comprehensive evaluation of the methods for estimation of the departure of the looped rating curves from the steady ones nor for identifying the most appropriate means to dynamically capturing hysteresis for different river flow conditions. However, there are instruments, analytical tools and legacy data available to improve our understanding of the significance of this effect and for developing appropriate protocols for its assessment in a systematic manner. Capturing new experimental evidence on looped rating curves irrespective of their construction approach (stage-discharge, index velocity, or slope-area method) can be attained through adoption of fast-sampling instruments and event-based sampling protocols. By doing so, we can remove a conceptual uncertainty in the construction of rating curves. The paper presents conceptual and experimental evidence to illustrate some of the unsteady flow impacts on rating curves and suggest lines of research and practical actions to enhance the accuracy of the current protocols for continuous stream flow estimation for both steady and unsteady river conditions.
Year: 2013