Ground-surface water interactions and the role of the hyporheic zone

Abstract

The hyporheic zone describes a region beneath and lateral to the bed of a stream where groundwater and surface water interact. Although the existence of this zone is well recognised, the flow dynamics and mixing processes within the zone are not well understood. To investigate hyporheic zone behavior, numerical groundwater flow models were developed with MODFLOW and calibrated using data collected at a study site on the Magpie River, near Wawa, Ontario, Canada. These models were used to examine the uncertainties of hyporheic zone behaviour at pool-riffle sequences and the response of the hyporheic zone to stream flow regulation. The hyporheic zone was found to be complex and temporally sensitive to stream stage and to groundwater fluxes as determined by streambed permeability and the hydrogeological characteristics of adjacent aquifers. The size of the hyporheic zone was found to be inversely proportional to the flux of groundwater moving towards the stream, and rapid changes in river stage were determined to cause short-term reversals of flow within the hyporheic zone which have important implications on hyporheic zone organisms and their need to adapt to changing environmental conditions.