Case Study: Scaling Recharge Rates from Pilot Projects of Managed Artificial Aquifer Recharge in the Walla Walla Basin, Oregon

Abstract

Recharge rates evaluated from pilot projects of surface managed aquifer recharge are extrapolated to develop design criteria for full-scale projects. Field experiments at surface-managed artificial aquifer recharge facilities in the Walla Walla River basin, Oregon, United States, were used to estimate recharges rates in relation to groundwater mounding and to the expansion in surface area of infiltration basins. Analysis of the results shows that in the case scenarios where the water table mounding does not reach the infiltration basin floor (thereby maintaining an unsaturated zone between the water table and the infiltration basin), the recharge rates from pilot tests scale linearly with the basin’s surface area expansion. However, in the case where the groundwater mound reaches the bottom of the basin floor (thereby providing a full hydraulic connection between the infiltration basins and the aquifer), recharge rates should be extrapolated using the perimeter of the infiltration basin. The explanation for this effect is offered by evaluating the distribution of the water velocities at the infiltration basin floor as the length difference between aquifer thickness and the radius of the infiltration basins increases. These findings enable pilot project results to be used as design criteria for full scale projects.