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See detailAssessing the consequences of salinization in Saloum estuary system by land use and land cover change analysis
Dieng, Ndeye Maguette ULg; Dinis, Joel; Faye, Serigne et al

Conference (2012, October)

The saltwater contamination constitutes a serious problem in Saloum estuary, due to the intermittent and reverse tide flows of the Saloum River. This phenomenon is caused by the runoff deficit, which ... [more ▼]

The saltwater contamination constitutes a serious problem in Saloum estuary, due to the intermittent and reverse tide flows of the Saloum River. This phenomenon is caused by the runoff deficit, which forces the advance of saltwater 60 km upstream, contaminating surface water and, thus, causing the degradation of biodiversity and large areas of agricultural soils in this region. The present study aims to evaluate the consequences of saltwater contamination in the last three decades in this estuary by assessing the land cover dynamics over this period. Land cover dynamics evaluation consists in tracking the landscape changing process over time to identify land cover transitions. These transitions are closely related to the ecosystem state condition and can be used to assess the combined impacts of both natural and human-induced phenomena over a given period of time. In this study, a special attention was given to the mangrove degradation and to the temporal progression of the salty barren soils locally called “Tan”. The lost of mangrove areas to “Tan” and the general increase of salty barren soil areas can reflect the increase of the level of salinization in the study area over the time period under consideration. To fulfill this objective, four Landsat satellite images from the same season in the years 1984, 1992, 1999 and 2010 were used to infer a time series land use and land cover maps of the Saloum estuary area. In addition to satellite imagery, rainfall record was used to evaluate climatic variation in terms of high to low precipitation during the time span considered. [less ▲]

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See detailAssessing the effect of the CLPG mutation on the microRNA catalog of skeletal muscle using high-throughput sequencing.
Caiment, Florian ULg; Charlier, Carole ULg; Hadfield, Tracy et al

in Genome Research (2010), 20(12), 1651-62

The callipyge phenotype is a monogenic muscular hypertrophy that is only expressed in heterozygous sheep receiving the CLPG mutation from their sire. The wild-type phenotype of CLPG/CLPG animals is ... [more ▼]

The callipyge phenotype is a monogenic muscular hypertrophy that is only expressed in heterozygous sheep receiving the CLPG mutation from their sire. The wild-type phenotype of CLPG/CLPG animals is thought to result from translational inhibition of paternally expressed DLK1 transcripts by maternally expressed miRNAs. To identify the miRNA responsible for this trans effect, we used high-throughput sequencing to exhaustively catalog miRNAs expressed in skeletal muscle of sheep of the four CLPG genotypes. We have identified 747 miRNA species of which 110 map to the DLK1-GTL2 or callipyge domain. We demonstrate that the latter are imprinted and preferentially expressed from the maternal allele. We show that the CLPG mutation affects their level of expression in cis ( approximately 3.2-fold increase) as well as in trans ( approximately 1.8-fold increase). In CLPG/CLPG animals, miRNAs from the DLK1-GTL2 domain account for approximately 20% of miRNAs in skeletal muscle. We show that the CLPG genotype affects the levels of A-to-I editing of at least five pri-miRNAs of the DLK1-GTL2 domain, but that levels of editing of mature miRNAs are always minor. We present suggestive evidence that the miRNAs from the domain target the ORF of DLK1, thereby causing the trans inhibition underlying polar overdominance. We highlight the limitations of high-throughput sequencing for digital gene expression profiling as a result of biased and inconsistent amplification of specific miRNAs. [less ▲]

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See detailAssessing the effects of compositional heterogeneity on phylogenomic analyses
Baurain, Denis ULg; Beiko, Robert G.; Ragan, Mark A.

Conference (2005, November 04)

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See detailAssessing the effects of spatial discretization on large-scale flow model performance and prediction uncertainty
Wildemeersch, Samuel ULg; Goderniaux, Pascal; Orban, Philippe ULg et al

in Journal of Hydrology (2014), 510

Large-scale physically-based and spatially-distributed models (>100 km2) constitute useful tools for water management since they take explicitly into account the heterogeneity and the physical processes ... [more ▼]

Large-scale physically-based and spatially-distributed models (>100 km2) constitute useful tools for water management since they take explicitly into account the heterogeneity and the physical processes occurring in the subsurface for predicting the evolution of discharge and hydraulic heads for several predictive scenarios. However, such models are characterized by lengthy execution times. Therefore, modelers often coarsen spatial discretization of large-scale physically-based and spatially-distributed models for reducing the number of unknowns and the execution times. This study investigates the influence of such a coarsening of model grid on model performance and prediction uncertainty. The improvement of model performance obtained with an automatic calibration process is also investigated. The results obtained show that coarsening spatial discretization mainly influences the simulation of discharge due to a poor representation of surface water network and a smoothing of surface slopes that prevents from simulating properly surface water-groundwater interactions and runoff processes. Parameter sensitivities are not significantly influenced by grid coarsening and calibration can compensate, to some extent, for model errors induced by grid coarsening. The results also show that coarsening spatial discretization mainly influences the uncertainty on discharge predictions. However, model prediction uncertainties on discharge only increase significantly for very coarse spatial discretizations. [less ▲]

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See detailAssessing the environmental potential of carbon dioxide utilization: A graphical targeting approach
Dumont, Marie-Noëlle ULg; der Assen, Niklas Von; Sternberg, André et al

in Computer Aided Chemical Engineering (2012)

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See detailAssessing the environmental potential of carbon dioxide utilization: A graphical targeting approach
Dumont, Marie-Noëlle ULg

Conference (2012, July)

Carbon Capture and Utilization (CCU) has the potential to reduce both greenhouse gas emissions and fossil fuel use. However, the conversion of CO2 is intrinsically difficult due to its low energetic state ... [more ▼]

Carbon Capture and Utilization (CCU) has the potential to reduce both greenhouse gas emissions and fossil fuel use. However, the conversion of CO2 is intrinsically difficult due to its low energetic state. Thus, a positive environmental effect of a CO2-consuming reaction cannot be taken for granted. In this work, we therefore present a graphical method to identify promising reaction schemes using CO2 as a feedstock. Reactant mixtures leading to minimal life-cycle greenhouse gas (GHG) emissions are determined. The optimal reaction schemes strongly depend on the reactants’ global warming potential (GWP); in the case of CCU, the future GWP values of CO2 and H2 are particularly critical and subject to major uncertainty today. The graphical method therefore provides GWP targets for CO2 capture and H2 production technologies. The method is demonstrated for the production of methanol. Five optimal reaction schemes are identified depending on the GWP values of CO2 and H2. Thus, four threshold relations for the GWP of CO2 and H2 are derived showing directly under which conditions the utilization of CO2 as a feedstock is environmentally preferential. [less ▲]

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See detailAssessing the geographic resolution of exhaustive tabulation for geolocating Internet hosts
Siwpersad, S. S.; Gueye, Cheikh Ahmadou Bamba ULg; Uhlig, Steve

in Lecture Notes in Computer Science (2008, April 29)

Geolocation of Internet hosts relies mainly on exhaustive tabulation techniques. Those techniques consist in building a database, that keeps the mapping between IP blocks and a geographic location ... [more ▼]

Geolocation of Internet hosts relies mainly on exhaustive tabulation techniques. Those techniques consist in building a database, that keeps the mapping between IP blocks and a geographic location. Relying on a single location for a whole IP block requires using a coarse enough geographic resolution. As this geographic resolution is not made explicit in databases, we try in this paper to better understand it by comparing the location estimates of databases with a well-established active measurements-based geolocation technique. We show that the geographic resolution of geolocation databases is far coarser than the resolution provided by active measurements for individual IP addresses. Given the lack of information in databases about the expected location error within each IP block, one cannot havemuch confidence in the accuracy of their location estimates. Geolocation databases should either provide information about the expected accuracy of the location estimates within each block, or reveal information about how their location estimates have been built, unless databases have to be trusted blindly. [less ▲]

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See detailAssessing the impact of brightness temperature simulation adjustment conditions in correcting Metop-A SST over the Mediterranean Sea
Tomazic, Igor ULg; Roquet, Hervé; Le Borgne, Pierre

in Remote Sensing of Environment (2013)

Multispectral sea surface temperature (SST) algorithms applied to infrared (IR) radiometer data exhibit regional biases due to the intrinsic inability of the SST algorithm to cope with the vast range of ... [more ▼]

Multispectral sea surface temperature (SST) algorithms applied to infrared (IR) radiometer data exhibit regional biases due to the intrinsic inability of the SST algorithm to cope with the vast range of atmospheric types, mainly influenced by water vapor and temperature profiles. Deriving a SST correction from simulated brightness temperatures (BTs), obtained by applying a Radiative Transfer Model (RTM) to Numerical Weather Prediction (NWP) atmospheric profiles and first guess SST, is one of the solutions to reduce regional biases. This solution is envisaged in the particular case of Metop-A Advanced Very High Resolution Radiometer (AVHRR) derived SST. Simulated BTs show errors, linked to RTM, atmospheric profiles or guess field errors. We investigated the conditions of adjusting simulated to observed BTs in the particular case of the Mediterranean Sea over almost one year. Our study led to define optimal spatio/temporal averaging parameters of the simulation observation differences, both during day and night, summer and colder season and for two simulation modes: operational (with reduced vertical resolution – 15 levels – NWP atmospheric profiles and two days old analysis used as first guess SST) and delayed (full vertical resolution – 91 levels – and concurrent analysis used as first guess SST). Each BT adjustment has been evaluated by comparing the corresponding corrected AVHRR SST to the AATSR SST that we adopted as validation reference. We obtained an optimized result across all defined conditions and modes for a spatial smoothing of 15 deg and a temporal averaging between 3 and 5 days. Specifically, analyses based on 10 day averages showed that a standard deviation based criterion favors spatial smoothing above 10 deg for all temporal averaging, while a bias based criterion favors shorter temporal averaging during daytime (< 5 days) and higher spatial smoothing (> 10 deg) for nighttime. This study has shown also the impact of diurnal warming both in deriving BT adjustment and in validation results. [less ▲]

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See detailAssessing the impact of fungal diseases management on crops and environment. Using dynamic models in the case of foliar diseases in wheat
Bancal, Marie-Odile; Roche, Romain; Gabrielle, Benoit et al

Conference (2007, November 13)

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See detailAssessing the Impact of Public Holidays on Travel Time Expenditure: Differentiation by Trip Motive
Cools, Mario ULg; Moons, Elke; Wets, Geert

in Proceedings of the 89th Annual Meeting of the Transportation Research Board (DVD-ROM) (2010)

The impact of public holidays on the underlying reasons of travel behavior, namely the activities people perform and the trips made, is seldom investigated. Therefore, in this paper the impact of public ... [more ▼]

The impact of public holidays on the underlying reasons of travel behavior, namely the activities people perform and the trips made, is seldom investigated. Therefore, in this paper the impact of public holidays on travel time expenditure in Flanders, differentiated by trip motive, is examined. The data used for the analysis stem from a household travel survey that was carried out in 2000. The main modeling approach that is employed is the zero-inflated Poisson regression approach, which explicitly takes into account the inherent contrast between travelers and non-travelers. The zero-inflated Poisson regression models yield findings that are harmonious with international literature: socio-demographic variables, temporal effects and transportation preferences contribute significantly in unraveling the variability of travel behavior. In particular it is shown that public holidays have a non-ignorable impact on daily travel behavior. Triangulation of both quantitative and qualitative techniques seems a solid roadway for further illumination of the underpinnings of travel behavior. [less ▲]

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See detailAssessing the Impact of Public Holidays on Travel Time Expenditure: Differentiation by Trip Motive
Cools, Mario ULg; Moons, Elke; Wets, Geert

in Transportation Research Record: Journal of the Transportation Research Board (2010), 2157

The impact of public holidays on the underlying reasons for travel behavior, namely, the activities people perform and the trips made, is seldom investigated. Therefore, the effect of holidays on travel ... [more ▼]

The impact of public holidays on the underlying reasons for travel behavior, namely, the activities people perform and the trips made, is seldom investigated. Therefore, the effect of holidays on travel time expenditure in Flanders, differentiated by trip motive, is examined. The data used for the analysis stem from a household travel survey carried out in 2000. The zero-inflated Poisson regression approach is used; it explicitly takes into account the inherent contrast between travelers and nontravelers. The zero-inflated Poisson regression models yield findings that are harmonious with international literature: socio-demographic variables, temporal effects, and transportation preferences contribute significantly to unraveling the variability of travel behavior. In particular, it is shown that the effect of public holidays on daily travel behavior cannot be ignored. Triangulation of quantitative and qualitative techniques is a solid basis for insight into the underpinnings of travel behavior. [less ▲]

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See detailAssessing the impact of space and time resolution of brightness temperature simulation conditions in correcting SEVIRI SST over the Adriatic Sea
Tomazic, Igor ULg; Le Borgne, Pierre; Tudor, Martina et al

Conference (2012)

Majority of operational sea surface temperature (SST) infra-red (IR) products have small overall bias but exhibit higher absolute biases in specific regions. Previous studies [for example Tomazic et al ... [more ▼]

Majority of operational sea surface temperature (SST) infra-red (IR) products have small overall bias but exhibit higher absolute biases in specific regions. Previous studies [for example Tomazic et al., 2011] showed that over Adriatic Sea there is a positive summer bias sometimes exceeding 0.5 K. Methodology to decrease regional biases [Le Borgne et al., 2011], based on using atmospheric profiles, surface SST fields and radiative transfer model to simulate the non-linear split window SST (NLSST) algorithm error, was used to assess the impact of atmospheric profiles with different spatial resolution (ECMWF: 0.125 deg and ALADIN 2 km), different input surface SST fields (OSTIA 6 km and CNR UHR L4 1 km) and different time and space averaging criteria’s in deriving the algorithm correction. SST corrections derived for the NLSST Spinning Enhanced Visible and Infrared Imager (SEVIRI) algorithm for five months (July, October and December 2010 and March and July 2011) are validated with AATSR L2 SST fields and compared to already implemented regional correction procedure at Center de Meteorologie Spatiale (CMS) to assess the optimal combination of space and time averaging criteria’s and input fields. Results show that the best improvement for all available months and for both day and night is obtained when using spatial averaging over the whole domain in combination with time averaging between the last 15 and last 31 days both for day and night time analysis. Using higher resolution ALADIN atmospheric profiles with OSTIA input SST fields didn’t improve the SST correction compared to using combination of coarser ECMWF atmospheric profiles and OSTIA input SST. Small improvement, based only on analysis for two months in 2011, is obtained when using both higher spatial resolution atmospheric profiles (ALADIN) and higher resolution input SST fields (CNR UHR L4 1 km). The best improvement obtained for spatial averaging over the whole domain (Adriatic Sea) suggests that the domain should be more extended (to Mediterranean Sea) to derive optimal spatial averaging, while conclusion of improvement obtained when using both the higher spatial resolution atmospheric profiles and input SST field need extension of analysis on other months in 2010. [less ▲]

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See detailAssessing the Impact of Weather on Traffic Intensity
Cools, Mario ULg; Moons, Elke; Wets, Geert

in Proceedings of the 87th Annual Meeting of the Transportation Research Board (DVD-ROM) (2008)

The investigation of weather effects on traffic intensity is important from a road safety point of view, because traffic intensity is noted as the first and primary determinant of traffic safety. Next to ... [more ▼]

The investigation of weather effects on traffic intensity is important from a road safety point of view, because traffic intensity is noted as the first and primary determinant of traffic safety. Next to traffic safety, weather conditions affect other predominant traffic variables, namely traffic demand and traffic flow. Therefore the main objective of this study is the identification and comparison of weather effects on traffic intensity at different site locations. To assess the impact of weather conditions on traffic intensity, the upstream and downstream traffic of four traffic count locations are considered. The traffic intensity data originate from minute data coming from single inductive loop detectors, collected by the Flemish Traffic Control Center. Data concerning weather events were recorded by the Royal Meteorological Institute of Belgium. The main modeling philosophy envisaged in this study to identify and quantify weather effects is the linear regression approach. Most appealing result of this study for policy makers, is the heterogeneity of the weather effects between different traffic count locations, and the homogeneity of the weather effects on upstream and downstream traffic at a certain location. The results also indicated that snowfall, rainfall and wind speed have a clear diminishing effect on traffic intensity, while maximum temperature significantly increases traffic intensity. Further generalizations of the findings are possible by studying weather effects on local roads and by shifting the scope towards travel behavior. Simultaneously modeling of weather conditions, traffic intensity rates, collision risk and activity travel behavior is certainly a key challenge for further research. [less ▲]

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See detailAssessing the Impact of Weather on Traffic Intensity
Cools, Mario ULg; Moons, Elke; Wets, Geert

in Weather, Climate and Society (2010), 2(1), 6068

This paper focuses on the effect of weather conditions on daily traffic intensities (the number of cars passing a specific segment of a road). The main objective is to examination whether or not weather ... [more ▼]

This paper focuses on the effect of weather conditions on daily traffic intensities (the number of cars passing a specific segment of a road). The main objective is to examination whether or not weather conditions uniformly alter daily traffic intensities in Belgium, or in other words whether or not road usage on a particular location determines the size of the impacts of various weather conditions. This general examination is a contribution that allows policymakers to assess the appropriateness of countrywide versus local traffic management strategies. In addition, a secondary goal of this paper is to validate findings in international literature within a Belgian context. To achieve these goals, the paper analyzes the effects of weather conditions on both upstream (toward a specific location) and downstream (away from a specific location) traffic intensities at three traffic count locations typified by a different road usage. Perhaps the most interesting results of this study for policymakers are the heterogeneity of the weather effects between different traffic count locations, and the homogeneity of the weather effects on upstream and downstream traffic at specific locations. The results also indicate that snowfall, rainfall, and wind speed diminish traffic intensity, and high temperatures increase traffic intensity. Further generalizations of the findings might be possible by studying weather impacts on local roads and by shifting the focus of research toward travel behavior. [less ▲]

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See detailAssessing the impacts of present and future interannual climate variability on European ecosystems using a dynamic vegetation model
Dury, Marie ULg; Hambuckers, Alain ULg; Warnant, Pierre et al

Poster (2011, April)

Climate projections indicate changes in mean climate as well as in climate variability and frequency of extreme events for the end of the 21st century compared to present. Since many biological processes ... [more ▼]

Climate projections indicate changes in mean climate as well as in climate variability and frequency of extreme events for the end of the 21st century compared to present. Since many biological processes reach non-reversible thresholds (loss of ability to germinate, mortality, etc.) at some temperatures or soil water values, changes in climate variability have long-term consequences for ecosystem composition, functioning and carbon storage. The CARAIB dynamic vegetation model is used to evaluate and analyse how future climate variability will affect European ecosystems. We examine the impacts of climate change and associated drought episodes on primary productivity (NPP) as well as on fire intensity. CARAIB is driven by the ARPEGE/Climate model and three regional climate models from the European Union project ENSEMBLES (KNMI-RACMO2, DMI-HIRHAM5 and HC-HadRM3Q0 models) forced with the IPCC A1B emission scenario. We analyse the interannual climate variability simulated by those climate models and compare it with the observed climate variability (CRU TS 3.0 historical climate dataset) over the period 1961-1990. None of these climate models can reproduce accurately the present natural climate variability. Therefore, the present NPP interannual variability simulated by CARAIB using climate outputs from the climate models differs from the one obtained with observed climate. For instance, the NPP interannual variability obtained with the ARPEGE/Climate model is significantly overestimated in some parts of Europe, especially in the Mediterranean region, in France, in northern Germany and northern Poland, in the Balkans and in Ukraine. Since discrepancies between modelled and observed current climate variability may also affect NPP variability calculated for the future as well as the intensity and the frequency of severe drought periods and wildfires, comparing the terrestrial ecosystem evolutions obtained with a range of climate models allows to improve the assessment of climate change impacts on ecosystems in the future. Anyway the trend between the present and the future is expected to be more robust. The NPP interannual variability increases in the future with the four climate models as a result of more frequent and more severe soil water stress episodes in southern and Central Europe. The projected climate changes are also likely to induce increased fire risk in the Mediterranean region but also in Central Europe and Russia. [less ▲]

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See detailAssessing the impacts of technical and structure choices on groundwater model performance using a complex synthetic case
Wildemeersch, Samuel ULg

Doctoral thesis (2012)

According to the European Water Framework Directive (2000/60/EC) and the specific Groundwater Directive (2006/188/EC), Member States have to manage groundwater at the groundwater body scale and in an ... [more ▼]

According to the European Water Framework Directive (2000/60/EC) and the specific Groundwater Directive (2006/188/EC), Member States have to manage groundwater at the groundwater body scale and in an integrated way. Given the objectives of “good quantitative and qualitative status” of groundwater for 2015 stated by the Directive, end-users want to know the quantitative and qualitative evolution of groundwater for several scenarios. Physically-based and spatially-distributed groundwater flow and transport models constitute useful management tools in this context since they take explicitely into account the heterogeneity and the physical processes occuring in the subsurface for predicting system responses to future stress factors. However, at such a scale, groundwater flow and transport modelling is challenging due to (1) the complexity of geological and hydrogeological contexts, (2) the uneven level of characterisation knowledge, and (3) the representativity of measured parameters. Furthermore, such models require long execution times. As a consequence, a series of choices and simplifications are made for dealing with these issues. Therefore, the outstanding question is to know whether endusers’expectations can be met in spite of such choices and simplifications. This work focuses on choices and simplifications related to spatial discretisation and saturation–pressure relations in the unsaturated one. The influence of stress factor time resolution is also tested. Considering this general context, the objective of the present work is to evaluate the influence of some model technical (spatial discretisation) and structure (saturation–pressure relations) uncertainties on model results, parameter sensitivities, and optimisation performance in order to provide guidelines for model development. This is performed using a synthetic case inspired by typical groundwater bodies of Wallonia (Belgium). This synthetic case is used for obtaining reference observations in terms of flow rates and hydraulic heads. These reference observations are then compared with their simulated equivalent produced by simplified models differing by their spatial discretisation, their saturation–pressure relations in the unsaturated zone, or the time resolution of their stress factors. The simplified models are then ranked using several performance criteria measuring the discrepancies between reference observations and their simulated equivalent. This ranking leads to guidelines for large-scale groundwater flow model development with respect to typical end-users’ expectations. Whatever the time resolution of stress factors, the quantitative and qualitative analyses performed indicate that coarsening horizontal spatial discretisation deteriorates mainly the simulation of flow rates, coarsening vertical spatial discretisation deteriorates mainly the simulation of hydraulic heads, and (over)simplifying saturation–pressure relations in the unsaturated zone significantly impair the simulation of both flow rates and hydraulic heads. Although optimisation can compensate for errors induced by model technical and structure uncertainties, the improvement of model fit is limited, especially for the coarsest models. Furthermore, with respect to end-users’ expectations, the weighted least-square objective function is not always the most relevant criteria for optimising models. Therefore, it is essential to use specific performance criteria for evaluating model performance depending on the objectives of the study. The ideal would be to develop an end-users objective function for including such performance criteria in the optimisation process and stop the optimisation process once performance criteria would have reached the values specified by the end-users with respect to the objectives of the study. [less ▲]

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See detailAssessing the impacts of technical uncertainty on coupled surface/subsurface flow model predictions using a complex synthetic case
Wildemeersch, Samuel ULg; Goderniaux, Pascal ULg; Orban, Philippe ULg et al

Poster (2011, September)

According to the EU Water Framework Directive, Member States have to manage surface water and groundwater at the water body scale and in an integrated way. Flow and transport models constitute useful ... [more ▼]

According to the EU Water Framework Directive, Member States have to manage surface water and groundwater at the water body scale and in an integrated way. Flow and transport models constitute useful management tools in this context since they can predict system responses to future stresses. However, numerical modelling at such a scale faces specific issues linked to (1) the representation of the geological and hydrogeological complexity, (2) the uneven level of characterisation knowledge, (3) the representativity of measured parameters and variables in the field, and (4) the CPU time needed for solving the numerical problem. Assumptions and simplifications made for dealing with these issues can lead to a series of models differing by their complexity and by the reliability of their predictions. Consequently, modellers have to find a compromise between complexity and reliability. The main objective of this research is to estimate the impacts of technical uncertainty, which is the uncertainty related to the numerical implementation, on groundwater flow model predictions. To reach that objective, the methodology consists in comparing reference predictions (hydraulic heads and flow rates) of a complex and close to reality synthetic case with the predictions provided by a series of simplified models (coarse spatial discretisation, coarse time discretisation, simplified law in the unsaturated zone). The synthetic case reflects the main characteristics found in groundwater bodies of South Belgium (Condroz region of Wallonia), characterised by a succession of limestone synclines and sandstone anticlines. The numerical model is developed with the fully-integrated surface/subsurface flow and transport code HydroGeoSphere using a mesh refined along the surface water network (153027 nodes and 269872 elements). A 5-year reference transient simulation, with daily stress factors is performed. The simulated hydraulic heads and flow rates constitute the reference observations and predictions for the comparison with the simplified models. The simplified models tested differ by their horizontal (500 m vs. 1000 m element size) and vertical (8 layers vs. 3 layers) spatial discretisations, their time discretisation (daily vs. monthly stress factors), and the type of constitutive law used for simulating the unsaturated flow (linear vs. van Genuchten). The models are run with the same parameter values than those used in the reference model to evaluate the deterioration in model predictions due to technical uncertainty. Additionally, some of the models are calibrated with the inverse modelling code PEST to distinguish how far a model calibration can possibly compensate for technical uncertainty. Then, predictions from each simplified model are compared with the reference predictions of the synthetic case. Then, the simplified models are ranked using several model performance criteria. Results of this research provide guidelines for the numerical implementation of groundwater flow models at the water body scale with respect to specific groundwater management objectives. [less ▲]

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See detailAssessing the influence of crop management strategies on the distribution of soil water content by ERT
Chelin, Marie ULg; Parvin, Nargish ULg; Hiel, Marie-Pierre ULg et al

Poster (2013, December 20)

Amongst other functions, cover crops are known to increase the stability of the soil structure. Commonly, their suppression is realized by using conventional tillage, but that it has been demonstrated to ... [more ▼]

Amongst other functions, cover crops are known to increase the stability of the soil structure. Commonly, their suppression is realized by using conventional tillage, but that it has been demonstrated to damage the soil structure, which directly impacts the soil water content. The proposed alternatives vary in terms of date, depth and type of tillage. As the soil water content is a major factor in agriculture, it is essential to better understand the influence of the cover crop management on its spatio-temporal distribution. Recent studies demonstrated the relevancy of the electrical resistivity tomography (ERT) to estimate the three-dimensional soil water content distribution. However, only a few of them were performed under field conditions. This study aims at (i) validating the use of the ERT method to estimate the soil water content distribution under field conditions (ii) quantifying the influence of cover crop management on the dynamic of soil water content along the growing season of a maize crop and on Belgian soil types. Three types of cover crop management content will be daily monitored: strip tillage, spring tillage and winter tillage. In order to assess the impact of plants on the soil water distribution, an additional plot will be burned after winter tillage. ERT will be used on a surface of 2 m² for each cover crop management. The validation of the average soil water content will be attended by using Time Domain Reflectrometers (TDR) and suction cups. The water stock obtained by ERT will be validated by using data from a weather station for the estimation of the evapotranspiration and rainfall and minirhizotrons for the assessment of the root water uptake. [less ▲]

Detailed reference viewed: 29 (7 ULg)