Effects of Fluctuating River flow on Groundwater/Surface Water Mixing in the Hyporheic Zone of a Regulated, Large Cobble Bed River
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 recording river stage, 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 co-variance 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) = 2.9 x 10-4 cms-1), and the least at the most permeable location (K=8.0 x 10-3 cms-1). 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 to study hydrogeologic processes over relatively short time scales (i.e., days to weeks) that would require much longer periods of time to evaluate (i.e., months to years) in un-regulated systems.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 896329
- Report Number(s):
- PNNL-SA-46549; 400480000; TRN: US200703%%588
- Journal Information:
- River Research and Applications, 22(8):937-946, Journal Name: River Research and Applications, 22(8):937-946
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COLUMBIA RIVER
FLOW RATE
FLUCTUATIONS
HYDRAULIC CONDUCTIVITY
HYDROLOGY
PERMEABILITY
SEDIMENTS
SURFACE WATERS
WATER QUALITY
GROUND WATER
MIXING
hysteresis
hyporheic
groundwater/surface water interaction
hydraulic gradient
specific discharge
spawning gravels
permeability
hydraulic conductivity