Tracking Groundwater Discharge to a Large River using Tracers and Geophysics

Abstract

Few studies have investigated large reaches of rivers in which multiple sources of groundwater are responsible for maintaining baseflow. This paper builds upon previous work undertaken along the Fitzroy River, one of the largest perennial river systems in north-western Australia. Synoptic regional-scale sampling of both river water and groundwater for a suite of environmental tracers ((4) He, (87) Sr/(86) Sr, (222) Rn and major ions), and subsequent modeling of tracer behavior in the river, has enabled definition and quantification of groundwater input from at least three different sources. We show unambiguous evidence of both shallow "local" groundwater, possibly recharged to alluvial aquifers beneath the adjacent floodplain during recent high-flow events, and old "regional" groundwater introduced via artesian flow from deep confined aquifers. We also invoke hyporheic exchange and either bank return flow or parafluvial flow to account for background (222) Rn activities and anomalous chloride trends along river reaches where there is no evidence of the local or regional groundwater inputs. Vertical conductivity sections acquired through an airborne electromagnetic (AEM) survey provide insights to the architecture of the aquifers associated with these sources and general groundwater quality characteristics. These data indicate fresh groundwater from about 300 m below ground preferentially discharging to the river, at locations consistent with those inferred from tracer data. The results demonstrate how sampling rivers for multiple environmental tracers of different types-including stable and radioactive isotopes, dissolved gases and major ions-can significantly improve conceptualization of groundwater-surface water interaction processes, particularly when coupled with geophysical techniques in complex hydrogeological settings.

Formation waters discharge to rivers near oil sands projects

“…Our study, in addition to others (Gardner et al, ; Harrington et al, ; Hogan et al, ; Smerdon et al, ), provides evidence that deeply sourced, “fossil” groundwater and shallow, “young” groundwater can each have a large impacts on river water chemistry. Fossil groundwater—groundwater stored for more than 12,000 years—has been identified in over one hundred aquifer systems around the globe (Jasechko, ) and likely comprises more than half of all groundwater stored in the upper 1 km of the crust (Jasechko et al, ).…”

“…Synoptic river chemistry surveys (e.g., Cook, ; Harrington et al, ; Pai, Villamizar, & Harmon, ; Smerdon et al, ) were completed along three rivers in the AOSR: the Christina River, the Clearwater River, and the Athabasca River.…”

“…Both deep‐ and shallow‐sourced groundwaters impact the chemistry of many river systems and may play an important role in maintaining baseflow conditions (Gardner, Harrington, Solomon, & Cook, ; Harrington, Gardner, & Munday, ; Hogan, Phillips, Mills, & Chesley, ; Smerdon, Payton Gardner, Harrington, & Tickell, ). Saline groundwaters are known to enter rivers in the Athabasca Oil Sands Region (herein “AOSR”; Cowie, ; Gibson et al, ; Gue et al, ; Jasechko, Gibson, Birks, & Yi, ).…”

Global Isotope Hydrogeology―Review

“…Coupling isotopic data to reactive transport models may yield insights into connections among concentration‐discharge relationships and streamflow sources (L. Li, et al, ). More frequent research that combines geochemical‐based approaches with other techniques used to evaluate groundwater discharges could improve conceptual models describing groundwater connections with surface waters (geophysics—Harrington et al, ; temperature profiles—Xu et al, ; piezometric and solute concentration data—Rhodes et al, ; and measurements of well water levels along river corridors to quantify hydraulic gradients—Cook, ). Synoptic sampling of river waters has helped quantify groundwater discharges along rivers spanning approximately ones to tens of kilometers (Beisner et al, ; Campodonico et al, ; Harrington et al, ; Smerdon et al, ). Multiple geochemical tracers are measured and applied to assess groundwater inputs along rivers, including radiocarbon (Bourke et al, ), radon‐222 (e.g., Cook et al, , ; Cook, ; Cartwright et al, ; Campodonica et al, 2015; Cartwright & Gilfedder, ; Cartwright & Hofmann, ; Xie et al, ; Xu et al, ; Avery et al, ), helium‐4 (Gardner et al, ), and chloride or other major ion concentrations, strontium isotopes (e.g., Négrel et al, ; Shand et al, ).…”

On the limits of heat as a tracer to estimate reach-scale river-aquifer exchange flux

“…Reliably quantifying the exchange flux between a river and the adjacent groundwater is essential for conjunctive management of surface water and groundwater. A number of methods have been used for quantifying reach‐scale groundwater discharge into rivers, including differential flow gauging, tracer dilution gauging, environmental tracers, geophysics, temperature, and numerical modeling [ Briggs et al ., ; Cook et al ., ; McCallum et al ., ; Harrington et al ., ; Lowry et al ., ; Slater et al ., ]. Kalbus et al .…”