How Does Subsurface Characterization Affect Simulations of Hyporheic Exchange?

Abstract

We investigated the role of increasingly well-constrained geologic structures in the subsurface (i.e., subsurface architecture) in predicting streambed flux and hyporheic residence time distribution (RTD) for a headwater stream. Five subsurface realizations with increasingly resolved lithological boundaries were simulated in which model geometries were based on increasing information about flow and transport using soil and geologic maps, surface observations, probing to depth to refusal, seismic refraction, electrical resistivity (ER) imaging of subsurface architecture, and time-lapse ER imaging during a solute tracer study. Particle tracking was used to generate RTDs for each model run. We demonstrate how improved characterization of complex lithological boundaries and calibration of porosity and hydraulic conductivity affect model prediction of hyporheic flow and transport. Models using hydraulic conductivity calibrated using transient ER data yield estimates of streambed flux that are three orders of magnitude larger than uncalibrated models using estimated values for hydraulic conductivity based on values published for nearby hillslopes (10(-4) vs. 10(-7) m(2)/s, respectively). Median residence times for uncalibrated and calibrated models are 10(3) and 10(0) h, respectively. Increasingly well-resolved subsurface architectures yield wider hyporheic RTDs, indicative of more complex hyporheic flowpath networks and potentially important to biogeochemical cycling. The use of ER imaging to monitor solute tracers informs subsurface structure not apparent from other techniques, and helps to define transport properties of the subsurface (i.e., hydraulic conductivity). Results of this study demonstrate the value of geophysical measurements to more realistically simulate flow and transport along hyporheic flowpaths.

Hydrologic controls on hyporheic exchange in a headwater mountain stream

“…The stream corridor study reach encompasses approximately 600 m of the valley of Watershed 1 (WS01), a headwater catchment in the H. J. Andrews Experimental Forest (HJA) in the western Cascades, Oregon, USA (Figure a). This study reach is bound by distinct bedrock outcrops at the upstream and downstream extents, and at one intermediate location, allowing explicit model boundaries to be set [after Ward et al ., ]. The streambed is primarily step‐pool morphology.…”

A Comparison of Hyporheic Transport at a Cross‐Vane Structure and Natural Riffle

“…For in‐stream and piezometer data, fluid specific conductivity was analyzed. Times of first detection ( t first ) and the passage of 99% of the observed signal ( t 99 ) were calculated for each time series observed (after Mason et al ; Ward et al ). The duration of tracer detection was calculated as …”

“…Electrical resistivity (ER) tomography has emerged as a tool to minimize methodological limitations due to spatiotemporal variability in quantifying hyporheic transport processes in situ (e.g., Ward et al 2010Ward et al , 2011Ward et al , 2012aWard et al , 2013aCardenas and Markowski 2011;Toran et al 2012;Menichino et al 2014). Time-series analysis of individual pixels in ER inversion images has been used to characterize transport processes in numerical models (Kemna et al 2002), soil columns (Binley et al 1996), and in both two-dimensional (2D) and three-dimensional (3D) scale model studies (Slater et al 2000(Slater et al , 2002.…”

Empirical Equations to Predict the Characteristics of Hyporheic Exchange in a Pool‐Riffle Sequence

“…Numerical simulations, flume experiments, analytical analysis, and field studies have been used to investigate the scale, RT, and flux of HE in pool-riffle sequences and to analyze the factors that influence the HE (Storey et al 2003;Saenger et al 2005;Kasahara and Hill 2006;Marzadri et al 2010;Tonina and Buffington 2011;Trauth et al 2013;Ward et al 2013;Fox et al 2014;Marzadri et al 2015). Storey et al (2003) reported that the key factors that determine the HE are the hydraulic head differences along the streambed caused by the interactions between the surface flow and bedform geometry, streambed hydraulic conductivity, and groundwater flow.…”