Using Heat as a Tracer to Detect the Development of the Recharge Bulb in Managed Aquifer Recharge Schemes

Abstract

Managed Aquifer Recharge (MAR), the intentional recharge of aquifers, has surged worldwide in the last 60 years as one of the options to preserve and increase water resources availability. However, estimating the extent of the area impacted by the recharge operations is not an obvious task. In this descriptive study, we monitored the spatiotemporal variation of the groundwater temperature in a phreatic aquifer before and during MAR operations, for 15 days, at the LIFE REWAT pilot infiltration basin using surface water as recharge source. The study was carried out in the winter season, taking advantage of the existing marked difference in temperature between the surface water (cold, between 8 and 13 °C, and in quasi-equilibrium with the air temperature) and the groundwater temperature, ranging between 10 and 18 °C. This difference in heat carried by groundwater was then used as a tracer. Results show that in the experiment the cold infiltrated surface water moved through the aquifer, allowing us to identify the development and extension in two dimensions of the recharge plume resulting from the MAR infiltration basin operations. Forced convection is the dominant heat transport mechanism. Further data, to be gathered at high frequency, and modeling analyses using the heat distribution at different depths are needed to identify the evolution of the recharge bulb in the three-dimensional space.

Transport, dispersion, and degradation of nonpoint source contaminants during flood‐managed aquifer recharge

“…Across S2 simulations, the kinematic ratio, or ratio of celerity to velocity, of the flood‐MAR wetting front ranges 5.00–76.9. Similar offsets between celerity and velocity have been observed at recharge sites (Caligaris et al., 2022; Moeck et al., 2017; O'Leary et al., 2012) and in catchments (Beven, 2020; Kirchner, 2003; McDonnell & Beven, 2014), but they have received little discussion in the MAR literature. In the Supporting Information, we derive a parametric expression for the kinematic ratio ($$k$$) through the vadose zone, assuming steady, gravity‐dominated flow: $$$$\begin{equation} k = \frac{c}{v} = \frac{\theta }{2 (\theta - \theta _r)} {\left[1 + \frac{4S_e^{1/m} (1 - S_e^{1/m})^{m-1}}{1 - (1 - S_e^{1/m})^m} \right]},\end{equation}$$$$…”

“…Across S2 simulations, the kinematic ratio, or ratio of celerity to velocity, of the flood-MAR wetting front ranges 5.00-76.9. Similar offsets between celerity and velocity have been observed at recharge sites (Caligaris et al, 2022;Moeck et al, 2017;O'Leary et al, 2012) and in catchments (Beven, 2020;Kirchner, 2003;McDonnell & Beven, 2014), but they have received little discussion in the MAR literature. In the Supporting Information, we derive a parametric expression for the kinematic ratio (𝑘) through the vadose zone, assuming steady, gravity-dominated flow:…”