A Coupled Surface Water/Groundwater Model to Evaluate Residence Time and Location of the Hyporheic Flow in a Pool and Riffle Sequence

摘要

The hyporheic zone in pool and riffle sequences is recognized to be important for fish spawning as well as surface water/groundwater interactions. In this study, steady state water surface elevations are calculated and the groundwater flow is then modeled by using either a simple one-dimensional (1D) Dupuit approach or a two-dimensional (2D) horizontal/vertical model in boundary fitted coordinates. The model calculates the average residence time of hyporheic flow and the location of upwelling and downwelling discharges for an idealized pool and riffle sequence. A correction equation is established to get an easy and accurate estimate for residence time in (2D) model based on information obtained from solving the (1D) model. The maximum relative error in calculating the residence time in (2D) using the correction equation is found 10%. In all the runs, it is clear that the downwelling discharges are found at the downstream location of the pool while the upwelling discharges are found at the downstream location of the riffle. The maximum spatial difference between upwelling locations in the (1D) and (2D) groundwater model is found to be 2.25% of one wave length while the maximum difference between the downwelling locations is found to be 14.46% of one wave length. The (1D) groundwater model gives reasonable results in estimating the upwelling location.