Groundwater flow and residence times below a meso-tidal high-energy beach: A model-based analyses of salinity patterns and 3H-3He groundwater ages

A Multi-Method Approach for Quantification of In- and Exfiltration Rates from the Subterranean Estuary of a High Energy Beach

“…However, further extensive hydrochemical investigations from Waska et al (2019) as well as apparent 3 H-3 He ages from Grünenbaum et al (2020) indicated additional freshwater discharge at the LWL. Beck et al (2017), Waska et al (2019), and Grünenbaum et al (2020) presumed the ridge to function as a groundwater divide during unsaturated conditions (low tide). Recent numerical simulations based on measured salinities and 3 H-3 He data from Grünenbaum et al (2020) showed that the strength of the groundwater divide can regulate the groundwater flow in the STE leading to the formation of either a single freshwater exfiltration zone in the runnel (referred to as the "one-plume system") or two freshwater exfiltration zones at both runnel and LWL ("two-plume system").…”

“…In this study, 222 eq Rn was defined by the activity of a groundwater sample, that was retrieved from 2 m below surface in the runnel exfiltration zone in September 2018 (Supplementary Figure S3). According to modeling results from Beck et al (2017) and Grünenbaum et al (2020), pore water residence times at this location ranged between several months up to years and are, thus, sufficiently long to approximate 222 eq Rn. According to Tamborski et al (2017), residence time calculations have reasonable uncertainties when residence times are longer than 0.5 days, but shorter than 7 days.…”

“…The topography of such a high energy beach is subject to strong changes depending on erosion and sedimentation processes, especially during the storm flood season in winter (Dobrynin et al, 2010). Grünenbaum et al (2020) concluded that changes between a one-and two-plume system over time, as well as overlapping conditions at the study site as a function of beach topography, are likely.…”

“…Initial modeling approaches suggested that freshwater discharge occurs exclusively into the runnel (Beck et al, 2017). However, further extensive hydrochemical investigations from Waska et al (2019) as well as apparent 3 H-3 He ages from Grünenbaum et al (2020) indicated additional freshwater discharge at the LWL. Beck et al (2017), Waska et al (2019), and Grünenbaum et al (2020) presumed the ridge to function as a groundwater divide during unsaturated conditions (low tide).…”

“…Beck et al (2017), Waska et al (2019), and Grünenbaum et al (2020) presumed the ridge to function as a groundwater divide during unsaturated conditions (low tide). Recent numerical simulations based on measured salinities and 3 H-3 He data from Grünenbaum et al (2020) showed that the strength of the groundwater divide can regulate the groundwater flow in the STE leading to the formation of either a single freshwater exfiltration zone in the runnel (referred to as the "one-plume system") or two freshwater exfiltration zones at both runnel and LWL ("two-plume system"). The topography of such a high energy beach is subject to strong changes depending on erosion and sedimentation processes, especially during the storm flood season in winter (Dobrynin et al, 2010).…”