Differences in methods of quantifying the vertical hyporheic flow for streambank flow field

Abstract

One-dimensional analytical methods are generally used to estimate the vertical hyporheic velocity, and inevitably yield values that differ from the true values when assumptions are not satisfied. In this study, numerical simulations were used to determine the amount of errors in the vertical hyporheic flow from several 1D analytical methods, including the solutions from amplitude ratio, phase shift of temperature, and hydraulic gradient with depth, under gaining and losing conditions. Results demonstrate that the velocity at the shallow layer is generally higher than the velocity at the deeper layer. Horizontal flow dominates the hyporheic exchange in the streambank-aquifer continuum at distances further away from the central channel. The amplitude ratio method and gradient method estimate the vertical velocity well when the vertical flow dominates the hyporheic flow and the flow is upwelling; otherwise, these two methods yield very inaccurate results. The amplitude ratio method and phase shift method yield better results compared with the gradient method for the streambank area. Our simulations indicate that two or more 1D analytical methods should be used in conjunction, and that the multi-dimensional hydraulic heads should be measured via an appropriate monitoring network to more accurately understand the hyporheic flow of a streambank.