Sabine Sauvage

Ecology, Geochemistry, Hydrology

PhD
30.99

Publications

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    ABSTRACT: Hydrologic interaction between surface and subsurface water systems has a significant impact on water quality, ecosystems and biogeochemistry cycling of both systems. Distributed models have been developed to simulate this function, but they require detailed spatial inputs and extensive computation time. The SWAT model is a semi-distributed model that has been successfully applied around the world. However it has not been able to simulate the two way exchanges between surface water and groundwater. In this study, the SWAT-LU model – based on a catena method that routes flow across three landscape units (the divide, the hillslope and the valley) – was modified and applied in the floodplain of the Garonne River. The modified model was called SWAT-LUD. Darcy's equation was applied to simulate groundwater flow. The algorithm for surface water level simulation during flooding periods was modified and the influence of flooding on groundwater levels was added to the model. Chloride was chosen as a conservative tracer to test simulated water exchanges. The simulated water exchange quantity from SWAT-LUD was compared with the output of a 2D distributed model, 2SWEM. The results showed that simulated groundwater levels in the LU adjoining the river matched the observed data very well. Additionally, SWAT-LUD model was able to reflect the actual water exchange between the river and the aquifer. It showed that river water discharge has a significant influence on the surface-groundwater exchanges. The main water flow direction in the river/groundwater interface was from groundwater to river, water flowed in this direction accounted for 65 % of the total exchanged water volume. The water mixing occurs mainly during high hydraulic periods. Flooded water was important for the SW-GW exchange process, it accounted for 69 % of total water flowed from the river to the aquifer. The new module also provides the option of simulating pollution transfer occurring at the river/groundwater interface at the catchment scale.
    Full-text · Article · Jun 2016 · Hydrological Processes
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    ABSTRACT: Snow is an important hydrological reservoir within the water cycle, particularly when the watershed includes a mountainous area. Modellers often overlook water stocked in snow pack and its influence on water distribution, especially when only some portions of the watershed is snow dominated. Snow is usually considered to improve hydrological modelling statistics, but without any regard for the realism of its representation or its influence on the hydrological cycle. This is all the more true when semi-distributed models are used, often considered inadequate for spatially representing such phenomena. On the other hand, semi-distributed models are being increasingly used to realise water budget assessment at a regional scale and such studies should not be realised without a good representation of the snow pack. Lack of field measurements is also a frequent justification for avoiding validating simulated snow packs. In this study, remote sensing data provided by MODIS is combined with in situ data, enabling the validation of the snow pack simulated by the Soil and Water Assessment Tool (SWAT), a semi-distributed, physically-based model, implemented over a partly snow-dominated watershed. Snow simulation was performed without complex algorithms or calibration procedures, using the elevation bands option included in the model and related snow parameters. Representation of snow cover and hydrological simulation were achieved by a standard automatic calibration of the model, over the 2000-2010 period, performed by SWAT-Cup/SUFI2, using six hydrological gauging stations along the fluvial continuum downstream of the snow-dominated area. Results highlight three important points: (i) Set-up of elevation bands over mountainous headwater improved hydrological simulation performance, even well downstream of the snow-dominated area. (ii) SWAT produced a good spatial and temporal representation of the snow cover, using MODIS data, despite a slight overestimation at the end of the snow season on the highest elevation bands. A comparison of the model estimate of snowpack water content with in situ data revealed an underestimation in water content in the lower part of the watershed and a slight overestimation in its upper part. Those errors are linked and originate from difficulties of the model to incorporate very local spatial and temporal variations of the precipitation lapse rate. (iii) Elevation bands brought consistent changes in water distribution within the hydrological cycle of implemented watersheds, which are more in line with expected flow paths.
    No preview · Article · Nov 2015 · Journal of Hydrology
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    ABSTRACT: Hydrodynamic process in the largest freshwater lake in China, Poyang Lake from 2009 to 2011 was simulated by using the lake hydrodynamic model, EFDC. Results showed that simulated daily average water elevation and discharges consisted with in-situ observations. To better evaluate the model accuracy and solve the problem of field measurements deficiency, remote sensing data were employed to validate and analyze the model practicability more comprehensively. The water surface height and inundation area measured by Radar altimeter ENVISAT RA-2 and MODIS images correlated well with the model predictions, which indicated that the frequently changing dynamics of water in Poyang Lake could be effectively revealed by using hydrodynamic model. Furthermore, remote sensing techniques also provided theory for long-term validation from different perspectives.
    Full-text · Conference Paper · Jul 2015
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    ABSTRACT: The Soil and Water Assessment Tool (SWAT) model was used to assess the impacts of different land use scenarios on hydrological processes in the Fuhe watershed in Poyang Lake Basin, East China. A total of 12 model parameters were calibrated with observed monthly runoff data for 1982-1988 and validated for 1991-1998 for baseline conditions. The baseline test results of R 2 and Nash-Sutcliffe model efficiency (NSE) values ranged between 0.88 and 0.94 across the calibration and validation periods, indicating that SWAT accurately replicated the Fuhe watershed streamflow. Several different land use scenarios were then simulated with the model, focusing on the impacts of land use change on the hydrology of the watershed. The results of hypothetical scenario simulations revealed that surface runoff declined while groundwater recharge and evapotranspiration (ET) increased, as forest land, agriculture land and/or grassland areas increased, as well as when paddy field and urban areas decreased. These results further showed that forest land has a higher capacity to conserve the water as compared to pasture land. The results of the real scenario simulations revealed that urbanization is the strongest contributor to changes in surface runoff, water yield, and ET. Urbanization can be considered as a potential major environmental stressor controlling hydrological components.
    Full-text · Article · Jul 2015 · International Journal of Agricultural and Biological Engineering
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    Full-text · Conference Paper · Jun 2015
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    ABSTRACT: Global change is expected to increase the frequency of intense rainfall events and consequent flash floods across the Mediterranean coastal basins in the next decades. To date, few models are able to simulate hydrological processes at basin-scale at a reasonable time scale to describe these flash events with accurate details. They are often complex physically-based distributed models and do not capture below-ground processes. The SWAT model assumes several simplifications but has recently been upgraded to sub-daily time-step calculations. However, its sub-daily module has only been tested in small catchments (~1 km²). The objectives of this study were (1) to assess the ability of the SWAT model to simulate discharge and sediment fluxes at hourly time-step in the ~1400 km² Têt Mediterranean river basin (southwestern France) and (2) to assess the possible gain of model’s performance when using fine grids of climate stations and sub-basins representation. We modelled the Têt basin with two sub-basin delineations of 1500 and 25 ha drainage areas, and with three climate stations grids of hourly meteorological data (NCEP CFSR, 30 km; SAFRAN, 8 km; and Meso-NH, 500 m). We calibrated the 6 resulting Têt models at hourly time-step with the upgraded version of the SWAT-CUP autocalibration tool, based on the hourly measured discharge of 7 gauging stations (2000-2014) and on the hourly measured suspended sediment concentration of 1 gauging station (2003-2014). We then compared the performances of the 6 models. This ongoing work will provide guidance for future hourly time-step modelling with the SWAT model.
    No preview · Conference Paper · Jun 2015
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    ABSTRACT: Due to global change, the frequency of intense rainfall events and consequent flash floods are expected to increase in the next decades across the Mediterranean coastal basins. To date, few distributed models are able to simulate hydrological processes at basin-scale at a reasonable time scale to describe these flash events with accurate details. The MARINE model is one of them: it is a process-oriented fully distributed model operating dynamically at the rainfall event time-scale. Both infiltration and saturation excess are represented along with subsurface, overland and channel flows. It does not describe ground-water processes since the model's purpose is to simulate individual flood events during which ground-water processes are considered negligible. The SWAT model is a conceptual semi-distributed model assuming several simplifications in equations that dynamically simulates above- and below-ground processes. It has been recently upgraded to sub-daily time-step calculations. Considering the 1400 km² Têt Mediterranean river basin (southwestern France) as a case-study, the objective of this study was to assess and compare the performances of these two models when simulating the discharge at sub-daily time-step. We first calibrated the two models based on the same input dataset (topography, land-use, soil classes, and meteorological stations’ grid). We then compared the performances of the two models on a number of selected flood events. This ongoing work will contribute to assess the ability of the SWAT model to simulate discharge at sub-daily time-step.
    Full-text · Conference Paper · Jun 2015
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    Full-text · Article · Jun 2015 · Ecological Modelling
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    ABSTRACT: The CRUE-SIM project (2014-2017) is an interdisciplinary project that brings together atmosphere physicists, hydrologists and oceanographers to study and model flash floods across the Mediterranean region : it integrates water and sediment transport as a consequence of intense rainfall, from the catchment to the sea. The objectives of the project are (1) the coupling between atmosphere, ocean and sea with continental hydrological and hydrodynamic models and (2) the integration of the feedbacks and the forcing continuity from one compartment to the other along the brief but intense events that will be studied. Considering the 1400 km² Têt Mediterranean river basin (southwestern France) as a case-study, two hydrological models will be used at different time and spatial scales: the low resolution SWAT model outputs will be used as the inputs of the high resolution MARINE model, both using rainfall forcing from the Meso-NH atmospheric model. The feedback of the storm surge on the downstream part of the basin will be considered thanks to the SYMPHONIE ocean model. We will quantify the fluxes, at a sub-daily time-step, of water and of suspended particulate matter transported during floods from the soil to the river and from the river to the sea. The CRUE-SIM project is one of the research lines of the SEDILION project funded by RTRA-STAE focused on the transport of dissolved and sorbed matter during flash floods.
    Full-text · Conference Paper · Jun 2015
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    ABSTRACT: Most of the modeling works about the impact of climate change on the hydrologic regime of river focus on overland flows or, less frequently, on aquifer recharge, soil water content, reservoir storage or snow cover. This study considers all main components of the water cycle and tests the ability of the SWAT model to describe them for the Garonne catchment scale (50,000 km2). Applying the differential split sampling test, proposed by Klemeš (1986), SWAT temporal transposability is evaluated in face of land used changes and climatic statistics variation over a 50-year period (1960-2010). To achieve this, different calibrations have been realized, using SWAT-CUP and a data set from 21 gauging stations along the fluvial continuum. Performance of the discharge simulation is thereafter evaluated at a monthly time step, over this same period (1960-2010) along with the consistency of the simulation of various hydrological cycle component. Results highlight trends toward the water repartition at an annual scale within the watershed over the last decades. A global decrese of the Garonne river flow is observed, mainly due to the reduction of precipitation and a positive trend of the simulated evapotranspiration. A good ability of the SWAT model to assess variations of hydrological cycle components over past 50 years has been conclued in this work, enable its use for future variation of those same components over the next 50 years.
    No preview · Conference Paper · Jun 2015
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    ABSTRACT: As freshwater habitats are among the most endangered, there is an urgent need to identify critical areas for conservation, especially those that are home to endangered species. The Pyrenean desman (Galemys pyrenaicus) is a semi-aquatic mammal whose basic ecological requirements are largely unknown, hindering adequate conservation planning even though it is considered as a threatened species. Species distribution modelling is challenging for freshwater species. Indeed, the complexity of aquatic ecosystems (e.g., linear and hierarchical ordering) must be taken into account as well as imperfect sampling. High-quality and relevant hydrological descriptors should also be used. To understand the influence of environmental covariates on the occupancy and detection of the Pyrenean desman, we combine both a robust sign-survey data set (i.e. with genetic validation ensuring true presence information) and a hydrological model to simulate the flow regime across a whole catchment. Markovian site-occupancy analysis, taking into account sign detection and based on spatially adjacent replicates, indicated a positive influence of heterogeneity of substrate and shelters, and a negative influence of flow variability on Pyrenean desman detection. This valuable information should help to improve monitoring programs for this endangered species. Our results also highlighted a spatially clustered distribution and a positive influence of stream flow and number of tributaries on occupancy. Hence, modifications of flow regime (e.g. hydropower production, irrigation, climate change) and habitat fragmentation appear to be major threats for this species, altering the connectivity between tributaries and the mainstream river as well as between adjacent sub-catchments.
    Full-text · Article · Apr 2015 · Biological Conservation
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    ABSTRACT: In temporary (or intermittent) rivers the first storm event after a dry period is responsible for transferring large amounts of sediment and nutrients into water reservoirs, thereby justifying close monitoring. The objective of this study was to analyse the contribution of storm events to sediment and nutrient transport in the Enxoé temporary river (southern Portugal) using detailed monitoring collected during three hydrological years (September, 2010 to August, 2013), and identify possible sediment and nutrient source areas based on the interpretation of hysteresis in the concentration–discharge relationship. The Enxoé River was monitored for suspended sediment concentration (SSC), total phosphorus (TP), particulate phosphorus (PP), soluble reactive phosphorus (SRP), and nitrate (NO3−). An empirical model was used to describe changes in solute concentrations, and the magnitude and rotational patterns of the hysteretic loops. Twenty-one storm events were registered. SSC, TP, PP, SRP, and NO3− concentrations varied between 1.6 and 3790.1, 0.05–11.4, 0–7.6, 0–0.67, and 0–27.84 mg l− 1, respectively. The highest SSC, TP, and PP concentrations were registered during the first storm event after an extended drought period. Annual sediment yields (13–480 kg ha− 1 y− 1) and nitrate (4.4–45.5 kg ha− 1 y− 1) were relatively low, while phosphorus losses (0.04–0.96 kg ha− 1 y− 1) reached relatively high values during humid years. Sediment and phosphorus transport was influenced by the stream transport capacity and particle availability, whereas nitrate loads were influenced by rainfall, soil hydraulic characteristics, and land management. This work highlights the main processes involved in sediment and nutrients loads in a temporary river during storm events, with a quantification of the relevant elements.
    Full-text · Article · Apr 2015 · Catena
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    ABSTRACT: An excessive use of nitrogen in agricultural regions leads to nitrate pollution of surface and groundwater systems. The Alegria River watershed (Basque Country, northern Spain) is an agricultural area dominated by a Quaternary shallow aquifer that has suffered nitrate-related problems since the 1990s. Our objective was to use the SWAT hydrological water quality model for long-term backward simulation (1990-2011) considering main changes in management practices to determine their impact on water quality. Hydrology, crop yield, nitrogen losses and soil nitrogen budgets were simulated satisfactorily. Nitrogen budgets indicated that annual N inputs exceed outputs (which consider main N loss pathways), resulting in mean N surpluses of 114 and 65 kg ha-1 year-1 in the periods 1990-1999 and 2000-2011, respectively. In the long-term, trends in N surplus generally follow those of fertilization input, which directly affect groundwater nitrate concentration. The characteristics of the aquifer and non-point source pollution have enabled us to properly simulate the historical trends in N concentration in the Vitoria-Gasteiz aquifer.
    No preview · Article · Mar 2015 · Hydrological Sciences Journal/Journal des Sciences Hydrologiques
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    ABSTRACT: The study was conducted in the Shibetsu River watershed (SRW), Hokkaido, Japan, in order to examine the possibility of using the soil and water assessment tool (SWAT) to provide an understanding of sediment and particulate organic nitrogen (PON) and particulate organic phosphorous (POP) yields between 2003 and 2008. The SRW is a non-conservative catchment (the surface catchment lying on a continuous impervious horizon) and it is recognized that it receives external groundwater (EXT) from other watersheds. The EXT yield from each hydrologic response unit (HRU) was added to streamflow in the SWAT model. Simulated daily sediment and PON and POP yields from the SWAT model showed a strong agreement with the observed values.
    Full-text · Article · Jan 2015 · Annales de Limnologie - International Journal of Limnology
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    ABSTRACT: Nitrate (NO3-) contamination of freshwater systems is a global concern. In alluvial floodplains, riparian areas have been proven to be efficient in nitrate removal. In this study, a large spatio-temporal dataset collected during one year at monthly time steps within a meander area of the Garonne floodplain (France) was analysed in order to improve the understanding of nitrate dynamic and denitrification process in floodplain areas. The results showed that groundwater NO3- concentrations (mean 50mg NO3- L-1) were primarily controlled by groundwater dilution with river water (explaining 54% of NO3- variance), but also by nitrate removal process identified as denitrification (explaining 14% of NO3- variance). Dilution was controlled by hydrological flow paths and residence time linked to river-aquifer exchanges and flood occurrence, while potential denitrification (DEA) was controlled by oxygen, high dissolved organic carbon (DOC) and organic matter content in the sediment (31% of DEA variance). DOC can originate both from the river input and the degradation of organic matter (OM) located in topsoil and sediments of the alluvial plain. In addition, river bank geomorphology appeared to be a key element explaining potential denitrification hot spot locations. Low bankfull height (LBH) areas corresponding to wetlands exhibited higher denitrification rates than high bankfull height (HBH) areas less often flooded. Hydrology determined the timing of denitrification hot moments occurring after flood events. These findings underline the importance of integrating dynamic water interactions between river and aquifer, geomorphology, and dual carbon source (river and sediment) when assessing nitrate dynamics and denitrification patterns in floodplain environments.
    No preview · Article · Jan 2015
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    ABSTRACT: Suspended sediment transportation and associated pollutants from catchment to stream networks are responsible for aquatic habitat degradation, reservoir sedimentation and the transportation of sediment bound pollutants. Quantifying suspended sediment loads from lands to watercourses is essential in controlling soil erosion and in implementing appropriate mitigation practices to reduce stream sediment and associated pollutant loads, and hence improve surface water quality downstream.The main objective of this study is to evaluate the temporal variability of hydrology, sediment and nickel loads using Soil and Water Assessment Tool in Oka watershed located in north Spain. Model simulation was completed using 11 years historical records (2001-2009 for validation and 2009-2012 for calibration) of streamflow and suspended sediment concentration (SSC). Thestreamflow, SSC and sediment load estimated from the model were compared with observed data using statistical parameters, which indicates a successful simulation. The annual production of simulated sediments shows variability between 662 and 1515 t, with a mean specific yield of 33 t km-2 y-1. The annual load of nickel simulated ranged from 32 to 72 kg, representing a mean specific of 1.63 kg km-2 year-1. The information obtained from this research is of interest to understand long term interannual variability of suspended sediment and nickel yield.
    No preview · Article · Jan 2015 · Annales de Limnologie - International Journal of Limnology
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    ABSTRACT: The modelling of trace metals (TM) in rivers is highly dependent on hydrodynamics, the transport of suspended particulate matter (SPM) and the partition between dissolved and particulate phases. A mechanistic, dynamic and distributed model is proposed that describes the fate of trace metals in rivers with respect to hydrodynamics, river morphology, erosion-sedimentation processes and sorption– desorption processes in order to identify the most meaningful parameters and processes involved at the reach scale of a large river. The hydraulic model is based on the 1-D Saint Venant equation integrating real transects to incorporate the river's morphology. The transport model of dissolved species and suspended sediments is based on advection–dispersion equations and is coupled to the one-dimensional transport with inflow and storage (OTIS) model, which takes transient storage zones into account. The erosion and sedimentation model uses Partheniades equations. Finally, the transfer of trace metals is simulated using two parameters, namely the partition coefficient (Kd) and the concentration of TM in the eroded material. The model was tested on the middle course of the Garonne River, southwest France, over an 80 km section under two contrasting hydrological conditions (80 m 3 s À1 and 800 m 3 s À1) based on measurements (hydrology, suspended sediments, particulate and dissolved metals fractions) taken at 13 sampling stations and tributaries. The hydrodynamic model was calibrated with discharge data for the hydraulic model, tracer experiments for the dissolved transport model and SPM data for the erosion-sedimentation model. The TM model was tested on two trace metals: arsenic and lead. Arsenic was chosen for its large dissolved fraction, while lead was chosen for its very important particulate fraction, thus providing contrasting elements. The modelling of TM requires all four processes to be simulated simultaneously. The presented model requires the calibration of ten parameters divided in four submodels during two hydrological conditions (low and high flow). All parameters could be explained by the physical properties of the case study, suggesting that the model could be applied to other case studies. The strategy of using different datasets under different hydrological conditions highlights: (a) the importance of transient storage in the study case, (b) a detailed description of the erosion and sedimentation processes of SPM, and (c) the importance of TM eroded from the sediment as a secondary delayed source for surface water. ã 2014 Elsevier B.V. All rights reserved.
    Full-text · Article · Oct 2014 · Ecological Modelling
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    Full-text · Dataset · Aug 2014
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    ABSTRACT: In agricultural watersheds, pesticide contamination in surface water mostly occurs during stormflow events. When modelling pesticide fate for risks assessment, the application timing input is one of the main uncertainty sources among all the parameters involved in the river network contaminations process. We therefore aimed to assess the sensitivity of the river network pesticide concentration patterns to application timing shifts within a plausible range of application dates, considering two pre-emergence herbicides (metolachlor and aclonifen) characterised by two different octanol/water partition coefficients (Kow). The Soil and Water Assessment Tool (SWAT) was applied in the 1110 km2 agricultural watershed of the river Save (south-western France), where wheat, maize, sorghum and sunflower are intensively grown. The pesticide application date was changed within a one-month interval and the pesticide concentration at catchment outlet was simulated from March to June 2010. Total metolachlor concentration prediction could be improved by an application timing shift to 3 days later (Daily R2 = 0.22 and PBIAS = − 57%). By testing the behaviour of the two molecules, it was shown that sorption processes were influencing the control of application timing on the transfer to surface water:metolachlor concentration in the channel depended on both discharge and delay between application date and first stormflow event whereas the transfer of aclonifen depended on rainfall intensity for exportation with suspended sediments through surface runoff. At last, the study discusses the potential implications of the sensitivity in terms of regional agricultural management practice design.
    Full-text · Article · Aug 2014 · Catena

  • No preview · Conference Paper · Jul 2014

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