Abstract
Abstract. Intercatchment groundwater flows (IGFs), defined as groundwater flows across topographic divides, can occur as regional groundwater flows that bypass headwater streams and only drain into the channel further downstream or directly to the sea. However, groundwater flows can also be diverted to adjacent river basins due to geological features (e.g., faults, dipping beds and highly permeable conduits). Even though intercatchment groundwater flows can be a significant part of the water balance, they are often not considered in hydrological studies. Yet, assuming this process to be negligible may introduce misrepresentation of the natural system in hydrological models, for example in regions with complex geological features. The presence of limestone formations in France and Belgium potentially further exacerbates the importance of intercatchment groundwater flows, and thus brings into question the validity of neglecting intercatchment groundwater flows in the Meuse basin. To isolate and quantify the potential relevance of net intercatchment groundwater flows in this study, we propose a three-step approach that relies on the comparison and analysis of (1) observed water balance data within the Budyko framework, (2) results from a suite of different conceptual hydrological models and (3) remote-sensing-based estimates of actual evaporation. The data of 58 catchments in the Meuse basin provide evidence of the likely presence of significant net intercatchment groundwater flows occurring mainly in small headwater catchments underlain by fractured aquifers. The data suggest that the relative importance of net intercatchment groundwater flows is reduced at the scale of the Meuse basin, as regional groundwater flows are mostly expected to be self-contained in large basins. The analysis further suggests that net intercatchment groundwater flow processes vary over the year and that at the scale of the headwaters, net intercatchment groundwater flows can make up a relatively large proportion of the water balance (on average 10 % of mean annual precipitation) and should be accounted for to prevent overestimating actual evaporation rates.
Highlights
Intercatchment groundwater flows are defined as groundwater fluxes crossing topographic divides, implying that precipitation falling in one catchment affects the streamflow in another catchment
The analysis of observed water balances in the Budyko framework shows that relatively small headwater catchments of the Meuse basin (50–700 km2; see Fig. 1) plot closest to or beyond the energy limit (Fig. 3b); this suggests that these catchments exhibit the highest potential for the presence of net intercatchment groundwater flows (IGFnet)
The net losses calculated with long-term observed runoff, precipitation and Turc–Mezentsev estimates of actual evaporation in these headwater catchments range between 70 mm yr−1, and 260 mm yr−1, with a median of 100 mm yr−1
Summary
Intercatchment groundwater flows are defined as groundwater fluxes crossing topographic divides, implying that precipitation falling in one catchment affects the streamflow in another catchment. L. Bouaziz et al.: Quantifying net intercatchment groundwater flows port water and large basins are likely self-contained (Schaller and Fan, 2009). Bouaziz et al.: Quantifying net intercatchment groundwater flows port water and large basins are likely self-contained (Schaller and Fan, 2009) This is based on the assumption that regional flow paths occur within surface drainage boundaries at the largest scale; systems with dipping sedimentary beds can divert groundwater away from the basin, leading to complications of the above-described theories and to intercatchment groundwater flows between adjacent basins (Schaller and Fan, 2009; Frisbee et al, 2016). Regional flow paths within a basin and between adjacent basins are the subject of this study as they characterize intercatchment groundwater flows
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