Effects of fluctuating river flow on groundwater/surface water mixing in the hyporheic zone of a regulated, large cobble bed river

Abstract

Physicochemical relationships in the boundary zone between groundwater and surface water (i.e. the hyporheic zone) are controlled by surface water hydrology and the hydrogeologic properties of the riverbed. We studied how sediment permeability and river discharge altered the vertical hydraulic gradient (VHG) and water quality of the hyporheic zone within the Hanford Reach of the Columbia River. The Columbia River at Hanford is a large, cobble-bed river where water level fluctuates up to 2 m daily because of hydropower generation. Concomitant with river stage recordings, continuous readings were made of water temperature, specific conductance, dissolved oxygen and water level of the hyporheic zone. The water level data were used to calculate VHG between the river and hyporheic zone. Sediment permeability was estimated using slug tests conducted in piezometers installed into the river bed. The response of water quality measurements and VHG to surface water fluctuations varied widely among study sites, ranging from no apparent response to covariance with river discharge. At some sites, a hysteretic relationship between river discharge and VHG was indicated by a time lag in the response of VHG to changes in river stage. The magnitude, rate of change and hysteresis of the VHG response varied the most at the least permeable location (hydraulic conductivity (K) ¼ 2.9 Â 10 À4 cms À1 ) and the least at the most permeable location (K ¼ 8.8 Â 10 À3 cms À1 ). Our study provides empirical evidence that sediment properties and river discharge both control the water quality of the hyporheic zone. Regulated rivers, like the Columbia River at Hanford, that undergo large, frequent discharge fluctuations represent an ideal environment in which to study hydrogeologic processes over relatively short time periods (i.e. days to weeks) that would require much longer periods (i.e. months to years) to evaluate in unregulated systems.

Spatio‐temporal variations of hyporheic flow in a riffle‐step‐pool sequence

“…This synchronous response seems to go against the 'conventional wisdom' that expects a switch between upwelling (gaining) and downwelling (loosing) conditions, in response to increased stage relative to the riparian water table (Figure 9a), e.g. Soulsby et al, 2001;Arntzen et al, 2006;Malcolm et al, 2006;Puckett et al, 2008. One rapid fall and rise of VHG appeared in the time series P1, associated with the last and highest flow peak on 3 August.…”

Investigation of the Hyporheic Zone at the 300 Area,Hanford Site

“…Slug testing of river tubes has been used to determine hydraulic conductivity within the hyporheic zone along the Hanford Reach (Arntzen et al 2006;Geist 2000). Slug tests were conducted by attaching an airtight pressure-regulating wellhead assembly to the top of each river tube.…”

Water table dynamics and groundwater–surface water interaction during filling and draining of a large fluvial island due to dam‐induced river stage fluctuations

“…Few field studies have investigated hyporheic exchange driven by dam operations. Recent studies examine the effects of dam-induced river stage fluctuations on hyporheic exchange in riverbeds and banks covering several kilometers, but with observations from usually one-dimensional transects at the meter scale [Arntzen et al, 2006;Curry et al, 1994;Hanrahan, 2008]; vertical head gradients are typically monitored along a few vertical profiles every several kilometers. However, the interactions between surface water and shallow groundwater are intrinsically three-dimensional and multiscale [Cardenas, 2008;Poole et al, 2006;Sophocleous, 2002;Storey et al, 2003], and the dynamics are impossible to completely comprehend with vertical profiles.…”