HyGage: Solving the Hysteresis Puzzle with a New Streamflow Monitoring Method

The questionable reliability of discharges obtained using the traditional stage–discharge method under gradually varied flow conditions continues to motivate the search for improved monitoring approaches that support water resources management, streamflow forecasting, and multipurpose scientific investigations related to the water cycle. This paper introduces HyGage, a new physically based monitoring method grounded in the governing equations of spatiotemporal, gradually varied, shallow open channel flow. The methodology integrates measurement elements commonly employed in the index velocity and slope area methods within a unified analytical framework, enabling real time discharge estimation in both steady and gradually varied flows without relying on the semi empirical techniques of the past. The performance of HyGage is evaluated by comparing its discharge estimates with those obtained from established methods. Unlike conventional approaches, HyGage is not built around any specific instrument; instead, it can flexibly incorporate combinations of immersed, close range, and remote sensing measurements through seamless integration.