3D Surface Water – Groundwater Interactions in a Large Experimental Channel

The Outdoor stream lab (OSL) operated by the National Center for Earth-surface Dynamics (NCED) is the venue for several interdisciplinary studies on stream hydrology and ecology. In collaboration with other investigators associated with NCED, we are studying the interactions between surface geomorphology and stream hydraulics with groundwater flow/ hyporheic exchange and residence times in the summer of 2008. Past studies have largely considered two dimensional exchange in flumes or horizontal flow paths along river banks. We hypothesize that three dimensional (3D) hydraulic exchange occurs at nested scales and is strongly tied to small scale (dunes) and large scale (unitbars and pointbars) geomorphic features. The OSL is the ideal facility to study these processes in three-dimensions since it has a sandy substrate prone to generation of bedforms while covering almost two wavelengths of a meandering channel. This poster presents results from a 3D piezometer network utilized to map physical hydrological attributes and to describe hyporheic and groundwater flow. In-situ pneumatic slug tests are utilized to map vertical profiles of hydraulic conductivity of OSL sediments. We will be presenting 3D hydraulic conductivity and head distributions. The OSL presents a rare opportunity to conduct field scale experiments within a known substrate and with well-defined and regulated boundary conditions- this allows for the development and validation of numerical computer models of coupled surface-subsurface processes. The result of this research extends our knowledge of the coupling between geomorphological and hydrological processes in fluvial corridors. The implications of this research will guide stream restoration efforts by establishing predictive process-based mechanisms driving the residence times of nutrients and other biologically important constituents.