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Summary: It is essential to be able to model the surface–subsurface flow processes that occur within and at the vicinity of channels and ditches because of their major role in groundwater recharge in arid regions. The main aim of this study was to evaluate a three-dimensional Richards’ equation-based modelling approach for simulating groundwater recharge. Another aim was to evaluate various strategies for estimating the hydraulic properties of the soil–aquifer system near the ditch. The case study consists of two infiltration experiments on a ditch in a catchment located in South-France. One experiment was used for calibrating the soil hydraulic properties by inverse modelling and the other for validation. The simulations were performed with the SWMS_3D simulation code, which computes three-dimensional saturated–unsaturated water flow and solute transport. For calibration and validation, two criteria were considered: piezometric heads at different distances from the ditch and hydraulic head profiles. Four scenarios of hydraulic parameter distribution were tested: an “a priori” scenario with observed values obtained by classical measurement techniques and three calibration scenarios. These are “homogeneous isotropic”, “heterogeneous isotropic” and “heterogeneous anisotropic” scenarios. The results obtained show that a three-dimensional Richards’ equation-based approach could satisfactorily simulate groundwater recharge by seepage losses from ditches in case of induced surface ponding experiment. Although a multi-criteria calibration was performed, three sets of soil hydraulic properties of various complexity that could reproduce satisfactorily the flow experiments were found. Finally, the results obtained also showed that representing the variability of soil properties in greater detail did not necessarily improve water flow simulation. The Akaike information criteria was used in order to discriminate between the well-calibrated scenarios. The “homogeneous isotropic” scenario represents the best compromise between goodness of fit and parsimony. The study also indicates that hydraulic heads are not necessarily sufficient for the thorough evaluation of groundwater flow models. [Copyright &y& Elsevier]

Summary: This study, based on a chemical and isotopic approach (major, trace elements and strontium isotopes), focuses on the geochemical hydrograph separation during flood events in a Mediterranean watershed (Hérault, Southern France). Major element contents present a typical decreasing logarithmic curve when plotted against river discharge. The concentrations measured during floods are, however, always higher than the theoretical dilution curve and can be related to (1) rainfall input in this sea-side basin, especially for Cl, and (2) water–rock interactions, which release elements in solution especially from the carbonate compartment of the watershed. Ca and HCO3 are not correlated with the river discharge, their content in the dissolved phase being controlled by calcite and aragonite mineral phases. Sr is a proxy of Ca regarding its physico-chemical properties, but it has been demonstrated that Sr is not controlled by these mineral phases and it presents a logarithmic variation with discharge. It is also very well correlated with Cl, which is a conservative element par excellence. Sr and its isotopic ratio can thus be used to constrain the geochemical behaviour of the dissolved phase during flood events. The main tributaries, characterised under various hydrological conditions, defined very well constrained end-members as the result of the diversity of the lithologies drained. Monitoring at the outlet of the watershed during four flood events showed that (1) during low flow periods, the signature at the outlet results from a binary mixing between the two main water sources in the basin; (2) each flood event studied presents a different temporal geochemical evolution (counter- or clockwise evolution in a 87Sr/86Sr vs. reciprocal Sr-content diagram) reflecting the predominance of different water sources during the flood, i.e., the tributaries versus the karst aquifers depending on rainfall intensity, duration and location; (3) the sequence of water origins during the flood seems also be controlled by the initial state of the soil and epikarst–karst continuum, inducing a more or less rapid and pronounced response after rainfall events. [Copyright &y& Elsevier]

Summary: This paper analyzed the seasonal dynamics of runoff-contributing areas in a small Mediterranean catchment (Can Vila catchment, 0.56km2). The aim was to provide a more detailed spatially distributed picture of the behavior of the catchment, which would help explain the high spatio-temporal variability of its hydrological response. Contributing areas for runoff were mapped during eight field surveys performed under varied hydrological conditions. Low permeable bare areas were recognised as classic source areas for infiltration excess runoff, and two types of saturated areas prone to saturation excess runoff were identified: A-type areas, linked to groundwater rising to the surface, and B-type areas, associated with saturation restricted to the upper soil profile. The amplitude of the seasonal variation in these saturated areas was similar to the amplitude found in more humid catchments, even if their decrease was more marked under dry conditions. In the Can Vila catchment, terraced topography promoted, however, more scattered saturation patterns than those usually described. A linear relationship between the extent of saturated areas and baseflow discharge was found; the relationship with the position of the water table was also direct, when saturated areas linked to groundwater rising dominated the saturation pattern. Using very simple methodology, a tentative quantification of the contribution of precipitation on saturated areas to storm-flow was performed, improving the overall understanding of the Can Vila Mediterranean catchment. [Copyright &y& Elsevier]