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This study investigates the influence of topography on the desaturation rates of groundwater-dependent wetlands in response to changes in recharge. We examined sixty catchments across northern Chile, which feature a wide variety of landforms. We categorized the landforms using geomorphon descriptors, identifying three distinct clusters: lowland, transition, and mountain settings. Using steady-state 3D groundwater models, we derived flow partitioning and seepage area extent for each catchment. Each cluster revealed consistent seepage areas evolution under varying wet-to-dry conditions. Our findings indicate that mountains exhibit reduced seepage area compared to lowlands at equivalent hydraulic conductivity to recharge (K/R) ratios but are less sensitive to recharge fluctuations with slower rates of seepage area variation. Statistical evidence demonstrates that geomorphons-defined landforms correlate with desaturation indicators, enabling the prediction of catchment sensitivity to climate change based solely on a topographic analysis. [ABSTRACT FROM AUTHOR]

To supplement the use of hydraulic tests and assess catchment-scale hydraulic conductivity (K), we propose a methodology for shallow aquifers only based on the Digital Elevation Model (DEM) and on the observation of the stream network. The methodology requires the groundwater system to be a main determinant of the stream density and extension. It assumes that the perennial stream network is set by the intersection of the groundwater table with the topography. The topographical structures and the subsurface hydraulic conductivity divided by the recharge rate K/R determine the groundwater table depth and the development of the stream network. Using a parsimonious 3D groundwater flow model, we calibrate K/R by minimizing newly defined distances between the simulated groundwater seepage zones and the observed stream network. Deployed on 24 selected headwater catchments from 12 to 141 km² located in north-western France, the method successfully matches the stream network in 80% of the cases and provides catchment-scale hydraulic conductivities between 9 x 10-6 and 9 x 10-5 m s-1 for shallow aquifers sedimentary and crystalline rocks. Results show a high sensitivity of K to the density and extension of the low-order streams and limited impacts of the DEM resolution as long the DEM remains consistent with the stream network observations. With the emergence of global remote-sensing databases combining information of highresolution DEM and stream network, this approach will contribute to assess hydraulic properties of in shallow headwater aquifers. [ABSTRACT FROM AUTHOR]

We used numerical modelling to explore the role of vertical compartmentalization of hillslopes on groundwater flow and recession discharge. We found that when hydraulic properties are vertically compartmentalized, streamflow recession behaviour may strongly deviate from what is predicted by groundwater theory that considers the drainage of shallow reservoirs with homogeneous properties. We further identified the hillslope configurations for which the homogeneous theory derived from the Boussinesq solution approximately hold and conversely for which it fails. By comparing the modelled recession discharge and the groundwater table dynamics, we identified the critical hydrogeological conditions responsible for the emergence of strong deviations. The three main controls are i) the contribution of a deep aquifer connected to the stream, ii) the heterogeneity in hydraulic properties, and iii) the slope of the interface between shallow permeable compartment and deep bedrock one with lower hydraulic properties. Our results confirm that a physical interpretation of the recession discharge exponent b from the classical equation -dQ/dt = aQb, and its temporal progression, are information that can only be interpreted with knowledge on structural configuration and heterogeneity of the aquifer. [ABSTRACT FROM AUTHOR]

Recession analysis is a classical method employed in hydrology to assess watersheds’ hydrological properties by means of the receding limb of a hydrograph, frequently expressed as the rate of change in discharge (dQ/dt) against discharge (Q). This relationship is often assumed to take the form of a power law −dQ/dt = aQb where a and b are recession parameters. Recent studies have highlighted major differences in the estimation of the recession parameters depending on the method, casting doubt on our ability to properly evaluate and compare hydrological properties across watersheds based on recession analysis. This study shows that estimation based on collective recessions as an average watershed response is strongly affected by the distributions event inter-arrival time, magnitudes, and antecedent conditions, implying that the resulting recession parameters do not represent watershed properties as much as they represent the climate. The clear conclusion is that proper evaluation of watershed properties using recession analysis requires considering individual recession events. [ABSTRACT FROM AUTHOR]