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Artificial recharge in urban and peri-urbans areas is not a typical practice, but the prolonged severe drought in central Chile has encouraged the study of this practice as an option for optimal and sustainable water management. The Andean piedmont of Santiago (Chile) has been urbanized that implies high water consumptions and increasing irrigation, which in turn acts as a new groundwater recharge. We simulated the period 1989-2015 using an integrated surface and subsurface model (WEAP-MODFLOW) to evaluate the impact of urbanization in groundwater recharge in a representative catchment in the area. An artificial recharge injection of 100 l/s (60,480 m3/day) was introduced in the model for a period of 26 weeks in a specific year (2009, between week 27 to 52, included). The recharge wells were implemented in key zones of the upper aquifer and monitoring wells were also implemented in different zones. The artificial recharge reproduced the hydraulic dome created by the infiltration flow, locally reaching a height of 6 m and beginning to dissipate approximately at 2.5 km (≤ 0.5 m) from the injection point. Moreover, we created a zone budget control section (2 km downstream) and we observed impacts on the water level in this sector, with a 1-year lag year after starting artificial recharge. The maximum impact was observed after approximately 1.5 years. Not only the study watershed has a high natural storage capacity, which benefits natural water retention, but its average residence time (4 years) is quite. Thus, our results could encourage different public or private stakeholders in the watershed to implement low impact development practices that could infiltrate water to cope with water shortage periods.

International audience; This paper emphasizes the importance of integrating outlet discharge and observed internal variables in the evaluation of distributed hydrological models outputs. It proposes a general methodology for a diagnostic evaluation of a complex distributed hydrological model, based on discharge data at the outlet and additional distributed information such as water level and surface soil moisture data. The proposed methodology is illustrated using the PUMMA model in the Mercier sub-catchment (6.6 km 2 ). Model parameters are specified according to field data and a previous study performed in a neighbouring catchment (Jankowfsky et al., 2014), without calibration. The distributed water level and soil moisture network of sensors were useful in the model evaluation process. Thus, model parameters are specified either using in situ information or results from previous studies. A stepwise approach is used for model evaluation. It includes standard water balance assessment as well as comparison of observed and simulated outlet discharge, whether on annual or event timescales. Soil moisture sensors are used to assess the ability of the model to simulate seasonal water storage dynamics based on a normalized index. The water level sensors network is used on two timescales: on a seasonal timescale, sensors network is used to assess the model's ability to simulate intermittency; whereas on event timescales, sensors network is used in determining the model's ability to reproduce observed reaction as well as response times. Event timescales do also focus on the correlation between hydrological response and either rainfall event or antecedent soil moisture variables. Results show that the non-calibrated model is quite effective at capturing water flow and soil water-storage dynamics, but it fails to reproduce observed runoff volume during events. There is strong indication of a deficiency in the characterization of catchment storage and upstream flowpath description. The soil water content and a network of water level sensors provide interesting information about soil moisture and river flow dynamics. They however fail to provide quantitative information about catchment storage. This study opens interesting perspectives for the evaluation of distributed hydrological models using hydrological signatures. Furthermore, it highlights the requirement of quantitative as well as qualitative signatures for improving such models.

Water resources management requires specialized computer tools that allow explicit integration of surface and groundwater fluxes, which generally have domains with different spatial discretization. On one hand, a surface hydrological domain, D1, is typically segmented in sub-basins, elevation contour bands or hydrological response units. These elements usually are represented by grids, triangles, or simple irregular polygons. In D1, the elements are connected to each other and incorporated into a drainage network that defines a surface topology, t1. On the other hand, an aquifer domain, D2, is organized in hydrogeological units, which can be represented by geometrical elements such as grids, triangulations, Voronoi or Quadratree diagrams. In D2, a regular connection is typically associated to structured meshes that defines a groundwater topology, t2. We present a new tool called GeoLinkage (v.geolinkage) that creates an ESRI-format linkage shapefile of the new surface-groundwater topology, t1-2. This python-based open-source tool has a graphical user interface (GUI) as an add-on for GRASS-GIS, which was constructed using Pygrass and Flopy libraries. It was developed to be used in WEAP-MODFLOV models, but it can also be used with other water resources management models. GeoLinkage allows processing models with reasonable computation times, which facilitates scenario analysis. It calculates the locations of the surface element geometries (nodes and arcs) using the GRASS platform and connects them to each element of a structured mesh in MODFLOW models. GeoLinkage was applied to obtain groundwater levels and coverage of water demand in Azapa Valley, a hyper-arid zone in the desert of Chile, where a grid of 70.305 cells and six fields with detailed geometry were processed in only 12 min.

International audience; The impact of urbanization on groundwater is by no means simple to understand, as it depends on a variety of factors such as climate, hydrogeology, water management practices and infrastructure. In semi-arid landscapes, the urbanization processes can involve high water consumptions and irrigation increase, which acts as a new groundwater recharge. We assessedes the hydrological impacts of urbanization and irrigation rates in an Andean peri-urban catchment located in Chile, in a semi-arid climate. For this purpose, we built and validated a coupled surface-groundwater model that allowed verifying a strong stream-aquifer interaction in areas with shallow groundwater, higher than some sewers and portions of the stream. Moreover, we also identified a significant local recharge associated with inefficient urban irrigation. From the evaluation of different future scenarios, we determined that increasing irrigation efficiency will decrease the current groundwater levels, while the median (Q50%) and low flow (Q95%) discharges will reduce from 408 l/s and 43 l/s to 389 l/s and 22 l/s respectively. Overall, our results show the relevance of integrating the modelling of surface and subsurface water resources at different spatial and temporal scales when assessing the effect of urban development and the suitability of urban water practices.

2D non-uniform polygonal meshes allow representation of the impact of landscape elements and small infrastructures on water flows. The initial vectorial mesh, derived from the intersection of several geographical information systems' layers, can have highly non-convex or sliver polygons. These bad-shaped elements compromise accurate numerical flow computation. We propose a flexible divide-and-conquer strategy to decompose polygons into physiographical meaningful parts using shape descriptors to better represent the surface terrain and hydrologic connectivity. We use the convexity index (CI) and the form factor (FF) to consider convex and square like optimum shapes. The strategy was applied to two peri-urban areas whose hydrologic response was simulated using distributed modeling. Good-quality meshes were generated with threshold values of CI≈0.8 and FF≈0.2, and CI≈0.95 and FF≈0.4 for undeveloped and highly urbanized zones, respectively. We concluded that the mesh segmentation facilitates the representation of the spatially distributed processes controlling not only the lumped response of the catchment, but also the spatial variability of water quantity and fluxes within it at medium and small scales.