Identification of floodplain and riverbed sediment heterogeneity in a meandering UK lowland stream by ground penetrating radar

Abstract

Complex spatial heterogeneity in riverbed and floodplain sediments control the spatio-temporal exchange of groundwater and surface water in the hyporheic zone, inducing hot spots of microbial activity and biogeochemical cycling. However, the characterization of hyporheic exchange dynamics has thus far failed to adequately account for the complex subsurface heterogeneity of river bed sediments in a spatial explicitly manner, in particular for highly complex lowland river bed sediments. Here we demonstrate the ability of ground penetrating radar (GPR) to efficiently map floodplain and river bed sediment structures within a lowland meandering river. The aim of this study was to delineate the type and spatial extent of complex, texturally heterogeneous facies of high and low conductive streambed materials. GPR surveys in this study involved not only state-ofthe-art terrestrial applications but also an aquatic survey conducted from a floating rig. The surveys revealed substantial sub-surface heterogeneity of depositional materials in the streambed and riparian zone. Eight characteristic radar facies were identified through the floodplain and groundtruthed against core samples and exposures of bank deposits. The majority of GPR profiles were dominated by trough-shaped depositional elements with erosional, curved, concave upward bounding surfaces, indicative of abandoned and chute stream channel structures. The identified abandoned channel structure was found to extend into the riverbed and to be filled by suspension fall-out fine-grained deposits (mud with organic matter and interbedded clay as indicated by observed signal attenuations). GPR proved to be a successful method to identify the spatial patterns of low conductivity peat and clay structures in the streambed and riparian zone of the investigated meander bend, highlighting its potential for larger scale analysis of these structures that have shown to control the exchange flow patterns between groundwater and surface water in lowland rivers.

Integrated Geophysical Investigation of River Ogun Floodplain, Papalanto, Southwestern Nigeria

“…This layer was referred to as topsoil. The material constituent of this component is recognized to have low permeability [44]. This layer has approximate thickness of about 0.5 m across the profiles.…”

“…Observation on the signal reflection indicates that t his layer is characterized with high moisture content which was considered to be saturated loamy clay soil with high amount of clay content. Any formation with this characteristic is considered to correspond with deposit of swamp and as such it is expected to be of a low permeability [44]. This particular layer exhibits this saturation all year round due to its low permeability feature that allows its ability for water retention for food crop farming within the floodplain in dry season.…”

Organizational Principles of Hyporheic Exchange Flow and Biogeochemical Cycling in River Networks Across Scales

“…The wider application of fluvial sedimentology principles (Dara et al., 2019) and understanding of alluvial depositional history (Słowik, 2014) provides further and perhaps underutilized predictive capacity for the spatial distributions of sediment properties in river valleys and their impact on hydrologic connectivity between streams and groundwaters, including, hyporheic exchange, residence time distributions, and biogeochemical reactivity in river channel and riparian sediments (Figure 6b). The potential for combining model‐based information of fluvial sediment transport to predict river valley and streambed sediment stratigraphy as controls of hyporheic exchange and hyporheic biogeochemical processes is currently untapped, leaving a great underutilized potential for achieving step changes in understanding of hyporheic zone processes across large catchments.…”

“…Resulting inter‐meander flow has been shown to control residence time distributions; and thus, redox zonation and nutrient turnover in sediments (Boano, Demaria, Revelli, & Ridolfi, 2010; Dwivedi et al., 2017). However to date from field studies, we rarely consider the vast spatial heterogeneity of hydraulic and hydrogeological properties of sediments between the river channel, the meanders, and floodplains (Figure 3d; Bersezio et al., 2007; Bridge et al., 1995; Dara et al., 2019), such as preferential flow through sub‐surface paleo‐channels (Lowell et al., 2009; Stanford & Ward, 1993; Słowik, 2014).…”

Subsurface imaging of fluvial deposits of the Vistula River valley in Kraków (southern Poland) by 2D ERT survey

“…Ground-pen e trat ing ra dar (GPR; e.g., Vandenberghe and Van Overmeeren, 1999;Kostic and Aigner, 2007;Schrott and Sass, 2008;S³owik, 2011;Dara et al, 2019), elec tro mag netic in duc tion (EMI; e.g., Conyers et al, 2008;De Smedt et al, 2011;Rejiba et al, 2018), and also elec tri cal re sis tiv ity to mog -ra phy (ERT; e.g., Baines et al, 2002;Giocoli et al, 2008;Cham bers et al, 2012;Torrese et al, 2013;Rey et al, 2013;Matys Grygar et al, 2016;Bábek et al, 2018;Hošek et al, 2018;Akinbiyi et al, 2019) are ef fec tive non-in va sive geo phys ical meth ods, widely used (in re cent times) to in ves ti gate as well as de ter mine the subsurface char ac ter iza tion of di verse de posits of flu vial or i gin. In par tic u lar, the lat est geo phys i cal method, i.e., ERT be long ing to the di rect cur rent (DC) re sis tiv ity methods, is ef fec tive in the rec og ni tion of un con sol i dated de pos its due to the fact that they re veal sig nif i cant vari a tion in elec tri cal re sis tiv ity.…”