Abstract
Located in the critical zone at the intersection between surface water and groundwater, hyporheic zones (HZ) host a variety of hydrological, biological and biogeochemical processes regulating water availability and quality and sustaining riverine ecosystems. However, difficulty in quantifying water fluxes along this interface has limited our understanding of these processes, in particular under dynamic flow conditions where rapid variations can impact large-scale HZ biogeochemical function. In this study, we introduce an innovative measurement assimilation chain for determining uncertainty-quantified hydraulic and thermal HZ properties, as well as associated uncertainty-quantified high-frequency water fluxes. The chain consists in the assimilation of data collected with the LOMOS-mini geophysical device with a process-based, Bayesian approach. The application of this approach on a synthetic case study shows that hydraulic and thermal HZ properties can be estimated from LOMOS-mini measurements, their identifiability depending on the Peclet number – summarizing the hydrological and thermal regime. Hydraulic conductivity values can be estimated with precision when greater than ~10−5m · s−1 when other HZ properties are unknown, with decreasing uncertainty when other HZ properties are known prior to starting the LOMOS-mini measurement assimilation procedure. Water fluxes can be estimated in all regimes with varying accuracy, highest accuracy is reached for fluxes greater than ~10−6m · s−1, except under highly conductive exfiltration regimes. We apply the methodology on in situ datasets by deriving uncertainty-quantified HZ properties and water fluxes for 2 data points collected during field campaigns. This study demonstrates that the LOMOS-mini monitoring technology can be used as complete and stand-alone sampling solution for quantifying water and heat exchanges under dynamic exchange conditions (time resolution < 15 min).
Highlights
Sustainable management of surface water and groundwater resources and of the ecosystems they support requires a reliable quantification of stream-aquifer water exchanges (Winter et al, 1998; Woessner, 2000; Stonestrom and Constantz, 2003; Fleckenstein et al, 2010)
We have proposed a new formulation for the Peclet number in the framework of surface-subsurface water exchange quantification using LOMOS-mini measurements (Equation 11) and demonstrated the strong relationship between this Peclet and estimates of hyporheic zone (HZ) properties, where regions of likely values do not cross the domain around Pe = 1
This study introduced a new solution for estimating HZ properties and surface-subsurface water exchanges, leveraging in situ LOMOS-mini measurements, numerical modeling and Bayesian inference
Summary
Sustainable management of surface water and groundwater resources and of the ecosystems they support requires a reliable quantification of stream-aquifer water exchanges (Winter et al, 1998; Woessner, 2000; Stonestrom and Constantz, 2003; Fleckenstein et al, 2010). The use of heat as a tracer is well-established thanks to the relatively low cost of temperature sensors and the ease of deployment (Lapham, 1989; Anderson, 2005; Constantz, 2008; Rau et al, 2014; Kurylyk and Irvine, 2019; Kurylyk et al, 2019). It is enabled by the relative stability of groundwater temperatures, whereas stream temperatures exhibit strong diurnal and annual cycles. The FiberOptic Distributed Temperature Sensing (FO-DTS) technology was introduced for hydrological applications, opening new opportunities for inferring patterns of groundwater discharge into streams continuously along the streambed (Selker et al, 2006a,b; Briggs et al, 2012)
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