A virtual flow meter to develop velocity-index ratings and evaluate the effect of flow disturbances on these ratings

Stream flow records are typically estimated with the use of empirical rating curves. The conventional rating method relates stage to discharge, however at sites prone to flow reversals, changes in stream bed roughness, backwater, and tidal effects, a stage-discharge rating is not unique and a velocity-index rating is often developed. A velocity-index rating relates the mean velocity of the channel and an index-velocity calculated by averaging velocities measured at defined locations and sampling intervals. The application of velocity index ratings assumes that the relation between the measured index velocity and the mean velocity in a cross-section is constant. This assumption is not valid if the channel experiences significant flow disturbances. This thesis presents a virtual flow meter developed to evaluate the effect of hydraulic factors such as vegetation growth, obstacles in a channel, and variable backwater on the stability of velocity-index rating curves. Velocity distributions obtained from a three dimensional computational fluid dynamics (CFD) model were used to simulate velocities measured by an in-situ instrument and used to develop velocity-index ratings for the various flow and channel conditions modeled. The virtual flow meter allowed for different instrument configurations to be tested (i.e. changing the number of beams, angle between beams, and orientation of instrument). This thesis evaluates the ability of a virtual flow meter to provide insight to both the effect of changes in flow and channel conditions, as well as changes in instrument configuration, on velocity-index ratings