Calibration of groundwater seepage against the spatial distribution of the stream network to assess catchment-scale hydraulic properties

Abstract

Abstract. The assessment of effective hydraulic properties at the catchment scale, i.e., hydraulic conductivity (K) and transmissivity (T), is particularly challenging due to the sparse availability of hydrological monitoring systems through stream gauges and boreholes. To overcome this challenge, we propose a calibration methodology which only considers information from a digital elevation model (DEM) and the spatial distribution of the stream network. The methodology is built on the assumption that the groundwater system is the main driver controlling the stream density and extension, where the perennial stream network reflects the intersection of the groundwater table with the topography. Indeed, the groundwater seepage at the surface is primarily controlled by the topography, the aquifer thickness and the dimensionless parameter K/R, where R is the average recharge rate. Here, we use a process-based and parsimonious 3D groundwater flow model to calibrate K/R by minimizing the relative distances between the observed and the simulated stream network generated from groundwater seepage zones. By deploying the methodology in 24 selected headwater catchments located in northwestern France, we demonstrate that the method successfully predicts the stream network extent for 80 % of the cases. Results show a high sensitivity of K/R to the extension of the low-order streams and limited impacts of the DEM resolution as long the DEM remains consistent with the stream network observations. By assuming an average recharge rate, we found that effective K values vary between 1.0×10-5 and 1.1×10-4 m s−1, in agreement with local estimates derived from hydraulic tests and independent calibrated groundwater model. With the emergence of global remote-sensing databases compiling information on high-resolution DEM and stream networks, this approach provides new opportunities to assess hydraulic properties of unconfined aquifers in ungauged basins.

Improving calibration of groundwater flow models using headwater streamflow intermittence

“…The transmissivities and associated hydraulic conductivities estimated in this study are consistent with values obtained from hydraulic tests or numerical groundwater models carried out in the similar region and lithological context (BRGM, 2018;Jiménez-Martínez et al, 2013;Kolbe et al, 2016;Le Borgne et al, 2006). More precisely, we find the same order of magnitude of K at 10 À5 m/s as in other studies carried-out on the Nançon catchment (Abhervé et al, 2023;Cornette et al, 2022;Dewandel et al, 2021) and the Canut catchment (Abhervé et al, 2023). The low porosity values estimated are consistent with the values found in the literature in crystalline bedrock contexts (Leray et al, 2012;Roques, 2013;Singhal & Gupta, 2010;Wyns et al, 2004).…”

“…In fact, we found that a non‐unique solution exists when only streamflow is considered, which poses a challenge in selecting a representative set of parameters. As already shown in Abhervé et al (2023), the extent of the stream network provides a constraint on groundwater level, allowing us to estimate the $$$ T/R $$$ ratio, and hence $$$ K $$$ by making assumptions on $$$ d $$$ and $$$ R $$$. Here, the approach is developed/extended in transient where the estimation of porosity relies on both the streamflow and the expansion/contraction of the hydrographic network.…”

“…In addition, we visually check that the spatial distribution of the simulated stream network is consistent with observed one. For quantitative validation, we also calculate the mismatch distance between simulated and observed stream networks based on the methodology of Abhervé et al (2023). From the pixels of the simulated stream network, we calculated the nearest downslope flowpath to the observed stream network $$$ {D}_{\mathrm{so}} $$$ [L], averaged as $$$ \overline{D_{\mathrm{so}}} $$$ [L].…”

“…In fact, we found that a non-unique solution exists when only streamflow is considered, which poses a challenge in selecting a representative set of parameters. As already shown in Abhervé et al (2023), the extent of the stream network provides a constraint on groundwater level, allowing us to estimate the T=R ratio, and hence K by making assumptions on d and R.…”

“…In the context of an unconfined aquifer with a defined thickness $$$ d $$$ [L], the hydraulic head $$$ h $$$ [L] is determined by the dimensionless ratio of hydraulic conductivity $$$ K $$$ [L/T] and recharge rate $$$ R $$$ [L/T], that is, $$$ K/R $$$ [−] (Goderniaux et al, 2013; Luijendijk, 2022). For a given recharge rate, the transmissivity $$$ T $$$ [L 2 /T], that is, the product of $$$ K $$$ and $$$ h $$$, controls the drainage density and the spatial extent of the stream network (Abhervé et al, 2023; Stoll & Weiler, 2010). Low transmissive aquifers display high groundwater levels and consequently dense stream networks in the upper part of the catchment, and conversely.…”