I am trying to determine the flow for which submergence occurs at a spillway modeled in 2D with the spillway modeled as a SA/2D connection. The applicable regulatory definition for submergence is “the difference between the water surface elevations upstream and downstream from a dam is one foot or less.”
Is this simply the Stage HW and Stage TW as given by HEC-RAS results for the SA/2D connection? Or should the upstream elevation be taken at a location where there are no drawdown effects from acceleration of flow over the spillway (“still water” elevation)?