From Grain to Floodplain: Evaluating heterogeneity of floodplain hydrostatigraphy using sedimentology, geophysics, and remote sensing

Abstract

Stratigraphy is a fundamental component of floodplain heterogeneity and hydraulic conductivity and connectivity of alluvial aquifers, which affect hydrologic processes such as groundwater flow and hyporheic exchange. Watershed‐scale hydrological models commonly simplify the sedimentology and stratigraphy of floodplains, neglecting natural floodplain heterogeneity and anisotropy. This study, conducted in the upper reach of the East River in the East River Basin, Colorado, USA, combines point‐, meander‐, and floodplain‐scale data to determine key features of alluvial aquifers important for estimating hydrologic processes. We compare stratigraphy of two meanders with disparate geometries to explore floodplain heterogeneity and connectivity controls on flow and transport. Meander shape, orientation, and internal stratigraphy affected residence time estimates of laterally exchanged hyporheic water. Although the two meanders share a sediment source, vegetation, and climate, their divergent river migration histories resulted in contrasting meander hydrofacies. In turn, the extent and orientation of these elements controlled the effective hydraulic conductivity and, ultimately, estimates of groundwater transport and hyporheic residence times. Additionally, the meanders’ orientation relative to the valley gradient impacted the hydraulic gradient across the meanders—a key control of groundwater velocity. Lastly, we combine our field data with remotely sensed data and introduce a potential approach to estimate key hydrostratigraphic packages across floodplains. Prospective applications include contaminant transport studies, hyporheic models, and watershed models. © 2019 John Wiley & Sons, Ltd.

Insight into the influence of local streambed heterogeneity on hyporheic-zone flow characteristics

“…Streambed geomorphology exerts a strong control on the hyporheic exchange processes (Findlay 1995;Azizian et al 2017) and spatial heterogeneities and local anomalies in sediment composition are thought to constrain the distributions in flow paths and residence times within the hyporheic zone (Mermillod-Blondin et al 2015;Malenda et al 2019). Here, a combination of geophysical and hydrological investigative methods was applied in a small boreal stream and the results emphasized the close connection between the spatial variability of local streambed structures, their hydraulic properties and the vertical extent of the hyporheic zone.…”

“…As electric permittivity can often be correlated to inherent conductivity of in-situ material and affects the reflection of radar waves (Reynolds 2011), GPR methods potentially could be used to identify sources of small-scale (0-0.5 m) heterogeneity in the hyporheic zone such as rocks or cobbles (Mermillod-Blondin et al 2015;Malenda et al 2019). A Malå 500-MHz GPR antenna was used to investigate the subsurface characteristics along the same measurement line as the ERT measurements.…”

“…The physical extent of the hyporheic zone and the degree to which it varies temporally and spatially is often both highly variable and dependent on the in-situ conditions such as bedform geometry (Cardenas et al 2004;Stonedahl et al 2010;Boano et al 2013;Mermillod-Blondin et al 2015;Malenda et al 2019), stream channel discharge (Maier and Howard 2011;Ward et al 2010;Stonedahl et al 2018;Wu et al 2018) and regional groundwater flow patterns (Marzadri et al 2016;Schmadel et al 2016). Additionally, heterogeneities in both streambed topography and sediment composition influence the hyporheic exchange (Malenda et al 2019).…”

“…The physical extent of the hyporheic zone and the degree to which it varies temporally and spatially is often both highly variable and dependent on the in-situ conditions such as bedform geometry (Cardenas et al 2004;Stonedahl et al 2010;Boano et al 2013;Mermillod-Blondin et al 2015;Malenda et al 2019), stream channel discharge (Maier and Howard 2011;Ward et al 2010;Stonedahl et al 2018;Wu et al 2018) and regional groundwater flow patterns (Marzadri et al 2016;Schmadel et al 2016). Additionally, heterogeneities in both streambed topography and sediment composition influence the hyporheic exchange (Malenda et al 2019). As such, even small heterogeneities in bed structure or hydraulic conductivity along a stream reach could have important implications for the exchange of energy and mass between surface water and the adjacent groundwater (Sawyer and Cardenas 2009;Bianchin et al 2011;Tonina et al 2016;Clémence et al 2017;Liu and Chui 2017).…”

Locating drainage tiles at a wetland restoration site within the Oak Openings region of Ohio, United States using UAV and land based geophysical techniques

“…All GPR data were processed using the Sensors & Software Inc.'s EKKO_Project software following standard GPR processing for subsurface utility identi cation (Annan, 2009;Jazayeri et al, 2018). We applied a time-zero correction and then 'dewowed' the signals with a high-pass lter to remove lowfrequency noise caused by inductive coupling effects or dynamic range limitations of the antennas (Annan, 2009;Malenda et al, 2019). We applied a Spherical Exponential Calibrated Compensation (SEC 2) time gain to all transects' signals to compensate for signal losses due to spherical spreading and ohmic losses caused by soil conductivity.…”