References of "Batelaan, Okke"
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See detailDrought-related vulnerability and risk assessment of groundwater in Belgium: estimation of the groundwater recharge and crop yield vulnerability with the B-CGMS
Jacquemin, Ingrid ULg; Verbeiren, Boud; Vanderhaegen, Sven et al

Poster (2016, April 19)

Due to common belief that regions under temperate climate are not affected by (meteorological and groundwater) drought, these events and their impacts remain poorly studied: in the GroWaDRISK, we propose ... [more ▼]

Due to common belief that regions under temperate climate are not affected by (meteorological and groundwater) drought, these events and their impacts remain poorly studied: in the GroWaDRISK, we propose to take stock of this question. We aim at providing a better understanding of the influencing factors (land use and land cover changes, water demand and climate) and the drought-related impacts on the environment, water supply and agriculture. The study area is located in the North-East of Belgium, corresponding approximatively to the Dijle and Demer catchments. To establish an overview of the groundwater situation, we assess the system input: the recharge. To achieve this goal, two models, B-CGMS and WetSpass are used to evaluate the recharge, respectively, over agricultural land and over the remaining areas, as a function of climate and for various land uses and land covers. B-CGMS, which is an adapted version for Belgium of the European Crop Growth Monitoring System, is used for assessing water recharge at a daily timestep and under different agricultural lands: arable land (winter wheat, maize...), orchards, horticulture and floriculture and for grassland. B-CGMS is designed to foresee crop yield and obviously it studies the impact of drought on crop yield and raises issues for the potential need of irrigation. For both yields and water requirements, the model proposes a potential mode, driven by temperature and solar radiation, and a water-limited mode for which water availability can limit crop growth. By this way, we can identify where and when water consumption and yield are not optimal, in addition to the Crop Water Stress Index. This index is calculated for a given crop, as the number of days affected by water stress during the growth sensitive period. Both recharge and crop yield are assessed for the current situation (1980 – 2012), taking into account the changing land use/land cover, in terms of areas and localization of the agricultural land and where the proportion of the different crops had considerably evolved through time (e.g., increase of grain maize and potatoes while winter cereals decrease). The preliminary results of the recharge lead to an average value in the area showing a significant negative trend, in both simulations with fixed (base = 1980) and changing land cover. In the same time, we could observe an increasing number of water stress periods, especially for maize, one of the main crops in the area. Finally, a preliminary test will be presented for the horizon 2040, for which we use meteorological time series (for high and low hydrologic impacts) given by the CCI-HYDR Perturbation Tool (Ntegeka V. and Willems P., 2009). This preliminary test aims to (1) evaluate the amplitude of the potential recharge deficit and, (2) especially, to define vulnerability zones, affected by frequent water stress, in connection with irrigation needs which could possibly increase the groundwater extraction. [less ▲]

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See detailQuantifying drought effects on groundwater recharge in a human-influenced catchment
Verbeiren, Boud; Huysmans, Marijke; Vanderhaegen, Sven et al

Conference (2015, June)

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See detailFactors controlling Si export from soils: A soil column approach
Ronchi, Benedicta; Barao, Lucia; Clymans, Wim et al

in Catena (2015), 133

The release of dissolved silicon (DSi) from A and B horizons was investigated with leaching tests on unsaturated columns. As forest A horizons have larger biogenic Si (BSi) pools than arable lands, we ... [more ▼]

The release of dissolved silicon (DSi) from A and B horizons was investigated with leaching tests on unsaturated columns. As forest A horizons have larger biogenic Si (BSi) pools than arable lands, we compared the Si release from a forest and a cropland from the same geographical region developed on a Luvisol in Belgium and a Cambisol in Sweden. The A horizons released a quickly dissolving Si fraction in contrast to the B horizons, which did contain no or only little amounts of BSi and released lower Si concentrations. Our experiments show that Si export from forest soils is high because of the presence of a large reservoir of soluble BSi as well as due to the acidity of the soil (pH<4). Leaching at two different water fluxes revealed that export in forest soils was transport controlled while cropland soils were in equilibrium. [less ▲]

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See detailDifferentiating between influencing factors land use and climate to assess drought effects on groundwater recharge in a temperate context
Verbeiren, Boud; Huysmans, Marijke; Vanderhaegen, Sven et al

Conference (2014, November)

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See detailLarge-scale stochastic optimization using non-stationary geostatistics for uncertainty assessment of groundwater flow and solute transport, in the framework of a near surface radioactive waste disposal
Rogiers, Bart; Laloy, E.; Gedeon, Matej et al

Poster (2014, July 09)

Uncertainty quantification is very much needed to support decision making related to e.g. environmental impact assessment for waste disposal sites. A probabilistic result provides a much stronger basis ... [more ▼]

Uncertainty quantification is very much needed to support decision making related to e.g. environmental impact assessment for waste disposal sites. A probabilistic result provides a much stronger basis for decision making compared to a single deterministic outcome. Accurate posterior exploration of high-dimensional and CPU-intensive models, which are often used for environmental impact assessment, is however a challenging task. To quantify the uncertainty associated with solute transport in the framework of a near surface radioactive waste disposal in Mol/Dessel, Belgium, we investigate combining the adaptive Metropolis (AM) McMC algorithm for updating the global model parameters, and adaptive spatial resampling (ASR) for updating of the spatially distributed model parameters, by block sampling. The forward model used is a groundwater flow model conditioned on borehole and direct push data, that accounts for non-stationary heterogeneity in hydraulic conductivity. The obtained flow solutions are used for solute transport simulations, and the results are compared with a different groundwater flow model parameterization, that makes use of homogeneous hydrogeological layers. Moreover, a number of simulations is performed to assess the effect of realistic dispersivity, which is derived from outcrop investigations. The obtained results indicate that the combination of AM and ASR using block sampling seems not to be very efficient for McMC sampling with the forward model used in this study. However, using the algorithm in optimization mode seems to work fine, and provides an alternate way for exploring the parameter space and the prediction uncertainty. [less ▲]

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See detailMulti-scale aquifer characterization and groundwater flow model parameterization using direct push technologies
Rogiers, Bart; Vienken, Thomas; Gedeon, Matej et al

in Environmental Earth Sciences (2014)

Direct push (DP) technologies are typically used for cost-effective geotechnical characterization of unconsolidated soils and sediments. In more recent developments, DP technologies have been used for ... [more ▼]

Direct push (DP) technologies are typically used for cost-effective geotechnical characterization of unconsolidated soils and sediments. In more recent developments, DP technologies have been used for efficient hydraulic conductivity (K) characterization along vertical profiles with sampling resolutions of up to a few centimetres. Until date, however, only a limited number of studies document high-resolution in situ DP data for three-dimensional conceptual hydrogeological model development and groundwater flow model parameterization. This study demonstrates how DP technologies improve building of a conceptual hydrogeological model. We further evaluate the degree to which the DP-derived hydrogeological parameter K, measured across different spatial scales, improves performance of a regional groundwater flow model. The study area covers an area of ~60 km² with two overlying, mainly unconsolidated sand, aquifers separated by a 5-7 m thick highly heterogeneous clay layer (in north-eastern Belgium). The hydrostratigraphy was obtained from an analysis of cored boreholes and about 265 cone penetration tests (CPTs). The hydrogeological parameter K was derived from a combined analysis of core and CPT data and also from hydraulic direct push tests. A total of 50 three-dimensional realizations of K were generated using a non-stationary multivariate geostatistical approach. To preserve the measured K values in the stochastic realizations, the groundwater model Krealizations were conditioned on the borehole and direct push data. Optimization was performed to select the best performing model parameterization out of the 50 realizations. This model outperformed a previously developed reference model with homogeneous K fields for all hydrogeological layers. Comparison of particle tracking simulations, based either on the optimal heterogeneous or reference homogeneous groundwater model flow fields, demonstrate the impact DP-derived subsurface heterogeneity in K can have on groundwater flow and solute transport. We demonstrated that DP technologies, especially when calibrated with site-specific data, provide high-resolution 3D subsurface data for building more reliable conceptual models and increasing groundwater flow model performance. [less ▲]

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See detailHigh resolution saturated hydraulic conductivity logging of friable to poorly indurated borehole cores using air permeability measurements
Rogiers, Bart; Winters, P.; Huysmans, Marijke et al

in Hydrogeology Journal (2014)

Saturated hydraulic conductivity (Ks) is one of the most important parameters determining groundwater flow and contaminant transport in both unsaturated and saturated porous media. This paper investigates ... [more ▼]

Saturated hydraulic conductivity (Ks) is one of the most important parameters determining groundwater flow and contaminant transport in both unsaturated and saturated porous media. This paper investigates the hand-held air permeameter technique for high resolution hydraulic conductivity determination on borehole cores using a spatial resolution of ~0.05 m. We test the suitability of such air permeameter measurements on friable to poorly indurated sediments to improve the spatial prediction of classical laboratory based Ks measurements obtained at a much lower spatial resolution (~2 m). About 368 Ks measurements were made on ~350 m of borehole cores originating from the Campine basin, Northern Belgium, while ~5230 air permeability measurements were performed on the same cores. The heterogeneity in sediments, ranging from sand to clayey sand with distinct clay lenses, resulted in a Ks range of seven orders of magnitude. Cross-validation demonstrated that using air permeameter data as secondary variable and laboratory based Ks measurements as primary variable increased performance from R2 = 0.35 for ordinary kriging (laboratory Ks only) to R2 = 0.61 for co-kriging. Due to the large degree of small-scale variability detected by the air permeameter, the spatial granularity in the predicted laboratory Ks also increases drastically. The separate treatment of Kh and Kv revealed considerable anisotropy in certain lithostratigraphical units, while others where clearly isotropic at the sample scale. Air permeameter measurements on borehole cores provide a cost-effective way to improve spatial predictions of traditional laboratory based Ks. [less ▲]

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See detailApplication of multi-scale variography for inferring the spatial variability of the hydraulic conductivity of a sandy aquifer
Rogiers, Bart; Vienken, Thomas; Gedeon, M et al

Poster (2014, April 28)

In the framework of the disposal of short-lived low- and intermediate-level radioactive waste in a near-surface disposal facility in Dessel (Belgium), extensive characterization of the hydraulic ... [more ▼]

In the framework of the disposal of short-lived low- and intermediate-level radioactive waste in a near-surface disposal facility in Dessel (Belgium), extensive characterization of the hydraulic conductivity (K) in the shallow Neogene aquifer has been performed at a regional scale. In the last few years the small-scale heterogeneity has been additionally characterized by outcrop analogue, hydraulic direct push, and borehole core air permeameter studies. The gathered data now include a) more than 350 hydraulic conductivity measurements on samples from 8 cored boreholes, mostly reaching depths of 50 m and data at 2 m intervals, b) more than 5000 air permeability measurements on the same borehole cores, c) more than 250 cone penetration tests (CPTs) with depths down to 40 m and data at 2 cm intervals, d) over 100 dissipation tests performed during the CPT campaigns, e) 17 direct push injections loggings, 6 hydraulic profiling tool logs, and 6 direct push slug tests, f) several hundreds of air permeability measurements on outcrop analogues of the aquifer sediments, and g) numerous grain size analyses. The current study aims to quantify the heterogeneity of K from the centimetre- to the kilometre-scale and to check the compatibility of the spatial variability revealed by the different datasets. This is achieved through gathering all K values (either direct measurements, calibrated relative K values, or K estimates from secondary data), and the use of variography to quantify spatial variability in terms of two-points geostatistics. The results are discussed, and the main differences between the different data sources are explained. In a final step, different multi-scale variogram models are proposed for capturing the main characteristics of multi-scale variability within the shallow Neogene aquifer in Belgium. [less ▲]

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See detailCombining flux estimation techniques to improve characterization of groundwater–surface-water interaction in the Zenne River, Belgium
Dujardin, Juliette; Anibas, Christian; Bronders, Jan et al

in Hydrogeology Journal (2014)

The management of urban rivers which drain contaminated groundwater is suffering from high uncertainties regarding reliable quantification of groundwater fluxes. Independent techniques are combined for ... [more ▼]

The management of urban rivers which drain contaminated groundwater is suffering from high uncertainties regarding reliable quantification of groundwater fluxes. Independent techniques are combined for estimating these fluxes towards the Zenne River, Belgium. Measured hydraulic gradients, temperature gradients in conjunction with a 1D-heat and fluid transport model, direct flux measurement with the finite volume point dilution method (FVPDM), and a numerical groundwater flow model are applied, to estimate vertical and horizontal groundwaterfluxes and groundwater–surface-water interaction. Hydraulic gradient analysis, the temperature-based method, and the groundwaterflow model yielded average verticalfluxes of–61,–45 and–40 mm/d, respectively. The negative sign indicates upwardflow to the river. Changes in exchangefluxes are sensitive to precipitation but the river remained gaining during the examined period. The FVPDM, compared to the groundwaterflow model, results in two very high estimates of the horizontal Darcyfluxes (2,600 and 500 mm/d), depending on the depth of application. The obtained results allow an evaluation of the temporal and spatial variability of estimated fluxes, thereby helping to curtail possible consequences of pollution of the Zenne River as final receptor, and contribute to the setup of a suitable remediation plan for the contaminated study site. [less ▲]

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See detailA System-based Paradigm of Drought Analysis for Operational Management
Tsakiris, Georges; Nalbantis, Ioannis; Vangelis, Harris et al

in Water Resources Management (2013), 27

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See detailThe usefulness of outcrop-analogue air-permeameter measurements for analysing aquifer heterogeneity: testing outcrop hydrogeological parameters with independent borehole data
Rogiers, Bart; Beerten, Koen; Smeekens, Tom et al

in Hydrology and Earth System Sciences (2013), 17

Outcropping sediments can be used as easily accessible analogues for studying subsurface sediments, especially to determine the small-scale spatial variability of hydrogeological parameters. The use of ... [more ▼]

Outcropping sediments can be used as easily accessible analogues for studying subsurface sediments, especially to determine the small-scale spatial variability of hydrogeological parameters. The use of cost-effective in situvmeasurement techniques potentially makes the study of outcrop sediments even more attractive. We investigate to what degree air-permeameter measurements on outcrops of unconsolidated sediments can be a proxy for aquifer saturated hydraulic conductivity (K) heterogeneity. The Neogene aquifer in northern Belgium, known as a major groundwater resource, is used as the case study. K and grain-size data obtained from different outcropping sediments are compared with K and grain-size data from aquifer sediments obtained either via laboratory analyses on undisturbed borehole cores (K and grain size) or via large-scale pumping tests (K only). This comparison shows a pronounced and systematic difference between outcrop and aquifer sediments. Part of this difference is attributed to grain-size variations and earth surface processes specific to outcrop environments, including root growth, bioturbation, and weathering. Moreover, palaeoenvironmental conditions such as freezing–drying cycles and differential compaction histories will further alter the initial hydrogeological properties of the outcrop sediments. A linear correction is developed for rescaling the outcrop data to the subsurface data. The spatial structure pertaining to outcrops complements that obtained from the borehole cores in several cases. The higher spatial resolution of the outcrop measurements identifies small-scale spatial structures that remain undetected in the lower resolution borehole data. Insights in stratigraphic and K heterogeneity obtained from outcrop sediments improve developing conceptual models of groundwater flow and transport. [less ▲]

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See detailUsing multiple point geostatistics for tracer test modeling in a clay-drape environment with spatially variable conductivity and sorption coefficient
Huysmans, Marijke; Orban, Philippe ULg; Cochet, Elke et al

in Mathematical Geosciences (2013), 46(5), 519-537

This study investigates the effect of fine-scale clay drapes on tracer transport. A tracer test was performed in a sandbar deposit consisting of cross-bedded sandy units intercalated with many fine-scale ... [more ▼]

This study investigates the effect of fine-scale clay drapes on tracer transport. A tracer test was performed in a sandbar deposit consisting of cross-bedded sandy units intercalated with many fine-scale clay drapes. The heterogeneous spatial distribution of the clay drapes causes a spatially variable hydraulic conductivity and sorption coefficient. A fluorescent tracer (sodium naphthionate) was injected in two injection wells and groundwater was sampled and analyzed from five pumping wells. To determine (1) whether the fine-scale clay drapes have a significant effect on the measured concentrations and (2) whether application of multiple-point geostatistics can improve interpretation of tracer tests in media with complex geological heterogeneity, this tracer test is analyzed with a local 3D groundwater flow and transport model in which fine-scale sedimentary heterogeneity is modeled using multiple-point geostatistics. To reduce memory needs and calculation time for the multiple-point geostatistical simulation step, this study uses the technique of "direct multiple-point geostatistical simulation of edge properties". Instead of simulating pixel values, model cell edge properties indicating the presence of irregularly-shaped surfaces are simulated using multiple point geostatistical simulations. Results of a sensitivity analysis show under which conditions clay drapes have a significant effect on the concentration distribution. Calibration of the model against measured concentrations from the tracer tests reduces the uncertainty on the clay drape parameters. The calibrated model shows which features of the breakthrough curves can be attributed to the geological heterogeneity of the aquifer and which features are caused by other processes. [less ▲]

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See detailRegional urban groundwater body risk assessment of contaminants using remotely sensed multi-resolution land-cover data
Batelaan, Okke; Dujardin, Juliette; Jamin, Pierre ULg et al

Conference (2013, September 15)

Contaminated sites are often the result of past relatively anarchic economical and industrial development. The last decades stakeholders are more aware of the risks posed by these sites. Within the Frac ... [more ▼]

Contaminated sites are often the result of past relatively anarchic economical and industrial development. The last decades stakeholders are more aware of the risks posed by these sites. Within the Frac-Weco project an integrated framework for the assessment, at regional scale, of the risks posed by these contaminated sites on water resources and ecosystems has been developed. The methodology is based on the calculation of contaminant fluxes reaching the receptors providing a way of estimating the level of exposure/degradation of these receptors at the groundwater body scale. The most important contamination problems at regional scale are located around old urban and industrialized areas. The land-cover distribution in these zones is of prime importance because it determines the spatial variation of groundwater recharge, which is the main vector of contaminant leaching from soil surface to groundwater. To obtain detailed information about land cover for groundwater recharge modeling, a stratified satellite image classification approach was adopted combining land-cover mapping at pixel level for the studied area as a whole with sub-pixel estimation of imperviousness within built-up zones. The obtained land-cover data is used as an input in the WetSpass model to simulate groundwater recharge at high resolution in spatially complex urban areas. In the next step the simulated groundwater recharge is used as an input in a regional scale groundwater flow and transport model simulating contaminant dispersion through the aquifer. Modeling results are further used to calculate a quality index for the whole groundwater body based on threshold values defined specifically for each contaminant. The approach proposed has been applied on the RWM073 groundwater body corresponding to the alluvial deposits of the Meuse River, Liège (Belgium). The high-resolution groundwater recharge estimations obtained by integrating remote sensing in the modeling procedure allow a better identification of the potential sources of contaminants and enable a proper quantification of total fluxes of contaminants from brownfields into the groundwater. The developed framework for regional risk assessment results in a global quality indicator for the groundwater body which can be used as input for decision-making. [less ▲]

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See detailDrought-related vulnerability and risk assessment of groundwater resources under temperate conditions
Verbeiren, Boud; Huysmans, Marijke; Tychon, Bernard ULg et al

Conference (2013, September)

Drought hazards are usually associated with (semi-)arid regions. Due to the assumed insignificance of drought hazards under temperate conditions this field remains poorly studied. This study aims at ... [more ▼]

Drought hazards are usually associated with (semi-)arid regions. Due to the assumed insignificance of drought hazards under temperate conditions this field remains poorly studied. This study aims at filling this gap by: (1) Increasing understanding of influencing factors determining drought in a temperate context; (2) Developing a methodology and quantitative tools aimed at planning and decision support with respect to groundwater management. In the first place drought is a phenomenon caused by deficient precipitation for a large area and significant duration and as such it is mainly a meteorological-related hazard. In case the temporary water deficiency affects groundwater bodies, the term groundwater drought is used. Groundwater droughts develop slowly but can have considerable socio-economic and environmental consequences. Groundwater drought is a complex phenomenon. Three main variables are important: groundwater recharge, groundwater level and groundwater discharge. Groundwater recharge is important as it is the source (inflow) of all groundwater. The groundwater table gives an indication of the storage, while groundwater discharge represents the outflow from the groundwater system. Next to natural meteorological variations also human induced factors play a role. In the Belgian context the main influencing factors determining the inflow and potentially resulting in a recharge deficit and an overall deterioration of groundwater resources are climate and land use/land cover. Groundwater demand for human activities has a direct effect on groundwater storage (level). The combined effect of these factors makes that some groundwater bodies are under pressure. In these groundwater bodies the outflow exceeds the inflow generating a reduction in storage and hence an unsustainable situation. A thorough knowledge of all three influencing factors and their interaction or combined effect is essential for a reliable estimate of the groundwater budget and a sustainable management. Hence, there is a need for an improved understanding of groundwater drought and the human-induced factors influencing the groundwater balance. This should form the basis for an integrated approach which allows tackling these negative effects and safeguarding sustainability of groundwater resources. [less ▲]

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See detailOpal-CT precipitation in a clayey soil explained by geochemical transport model of dissolved Si (Blégny, Belgium)
Ronchi, Benedicta; Barao, A.L.; Vandevenne, F. et al

Poster (2013, August 25)

Opal-CT precipitation controlling dissolved Si export Dissolved Si (DSi) exported by rivers are controlled by geological, hydrological and biological cycle processes [1]. The DSi concentrations measured ... [more ▼]

Opal-CT precipitation controlling dissolved Si export Dissolved Si (DSi) exported by rivers are controlled by geological, hydrological and biological cycle processes [1]. The DSi concentrations measured in a river of an upstream catchment in eastern Belgium (Blégny, Land of Herve) don’t vary seasonally (6.91±0.94mgL-1; n=363). Si concentrations in pore water are often higher and vary more (8.65±3.65mgL-1; n=128). The decrease of DSi along the flowpath of water is due to sink processes, i.e. precipitation, adsorption or uptake by vegetation. As the DSi in the river does not show any seasonal variation, uptake by vegetation can be ruled out [1] whereas precipitation or adsorption can control the DSi drained by the stream water. This hypothesis is confirmed by XRD and DeMaster analysis. At 0.1m depth the soil is constituted of 62% quartz, 7% K-feldspar, 6% plagioclase, 3.2% carbonates, 18.9% Al-clay, 1.47% Kaolinite, 0.63% Chlorite and 0.2% amorphous Si, probably of biogenic origin. At 1.5m depth, the amounts of several minerals (35.8% quartz, 0.6% K-feldspars, 0.9% plagioclase, Al-clay 14.7%) drop drastically. Carbonates, chlorite and kaolinite are absent whereas 40.4% opal-CT appears. The precipitation of opal-CT controls the DSi export of this catchment. Development of geochemical transport model To descripe DSi export from a catchment a geochemical transport model is developped in HP1 which couples the water flux model Hydrus with the geochemical model PHREEQC [2]. Our model is based on the conceptual model developped in [3]. First results show different DSi export dynamics in the unsaturated zone than in the aquifer due to different pCO2 values and varying soil moisture conditions. Further development of the model will help to find out the reason of opal-CT precipitation in this setting. [1]Fulweiler, Nixon (2005) Biogeochemistry 74:115–130. [2] Simunek, Jacques, van Genuchten, Mallants (2006) JAWRA 42:1537-1547. [3] Ronchi et al. (2013). Silicon, 5(1), 115–133. [less ▲]

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See detailThe usefulness of outcrop analogue air permeameter measurements for analyzing aquifer heterogeneity: quantifying outcrop hydraulic conductivity and its spatial variability
Rogiers, Bart; Beerten, Koen; Smeekens, Tuur et al

in Hydrological Processes (2013)

Saturated hydraulic conductivity (K) is one of the most important parameters determining groundwater flow and contaminant transport in both unsaturated and saturated porous media. Although several well ... [more ▼]

Saturated hydraulic conductivity (K) is one of the most important parameters determining groundwater flow and contaminant transport in both unsaturated and saturated porous media. Although several well-established laboratory methods exist for determining K, in situ measurements of this parameter remain very complex and scale dependent. Often, the limited accessibility of subsurface sediments for sampling means an additional impediment to our ability to quantify subsurface K heterogeneity. One potential solution is the use of outcrops as analogues for subsurface sediments. This paper investigates the use of air permeameter measurements on outcrops of unconsolidated sediments to quantify K and its spatial heterogeneity on a broad range of sediment types. The Neogene aquifer in northern Belgium is used as a case study for this purpose. To characterize the variability in K, 511 small-scale air permeability measurements were performed on outcrop sediments representative over five of the aquifer’s lithostratigraphic units. From these measurements, outcrop-scale equivalent K tensors were calculated using numerical upscaling techniques. Validation of the air permeameter-based K values by comparison with laboratory constant head K measurements reveals a correlation of 0.93. Overall, the results indicate that hand-held air permeameters are very efficient and accurate tools to characterize saturated K, as well as its small-scale variability and anisotropy on a broad range of unconsolidated sediments. The studied outcrops further provided a qualitative understanding of aquifer hydrostratigraphy and quantitative estimates about K variability at the centimetre-scale to metre-scale. [less ▲]

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See detailTowards a comprehensive framework for the assessment of groundwater drought in temperate regions
Tsakiris, Georges; Nalbantis, Ioannis; Vangelis, Harris et al

Conference (2013, June)

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See detailMulti-scale aquifer characterization and groundwater flow model parameterization using direct push technologies
Rogiers, Bart; Vienken, T; Batelaan, Okke et al

in Novel Methods for Subsurface Characterization and Monitoring: From Theory to Practice (2013, May)

Groundwater flow and contaminant transport models are used to support decision making regarding waste disposal options, sites contaminated by surface or subsurface sources, or to develop and test cost ... [more ▼]

Groundwater flow and contaminant transport models are used to support decision making regarding waste disposal options, sites contaminated by surface or subsurface sources, or to develop and test cost-effective groundwater remediation schemes. Such models are influenced by different sources of uncertainty, including those due to spatial variability in aquifer and aquitard properties including hydraulic conductivity (K). However, quantifying spatial variability in K remains challenging. Classical drilling techniques for shallow heterogeneous unconsolidated sedimentary deposits involving continuous coring are expensive and time-consuming, especially when the area of interest exceeds several tens of km². Alternative techniques such as direct push technologies use hydraulic rams, supplemented with vehicle weight, or high-frequency hammering, to advance small-diameter tools into the subsurface. These tools are typically used for cost-effective geotechnical characterization of unconsolidated deposits; recent developments also allow for hydraulic characterization. The depth of investigation is up to ~40 m, depending on the tools used (i.e applied load) and sediment properties (friction). Up to now, only a limited number of studies document using this type of data to parameterize regional groundwater flow models. To fill this gap, this study aims at parameterizing a regional groundwater flow model using data from various types of direct push technologies. We discuss the characterization of an area (~60 km²) near the nuclear zone of Mol/Dessel (Belgium), using various direct push technologies. Most of the measurements are concentrated in an area of 200×400 m². The data include 265 cone penetration tests (CPTs), 113 pore pressure dissipation tests (PPDTs), 17 direct push injection logs (DPIL), 6 hydraulic profiling tool (HPT) logs and 19 direct push slug tests (DPST). Resulting K values, either calculated or estimated, and the corresponding spatial variability are compared with that of borehole and outcrop studies. The benefit of using standard CPT data for the parameterization of an aquitard at the study site has previously been shown. The approach is now applied to the aquifer units and incorporates new direct push data for the entire upper ~40 m of the hydrogeological domain. The effect of the 3D heterogeneous hydraulic conductivity field on the performance of the groundwater flow model is discussed; the value of the different direct push technologies is equally addressed. [less ▲]

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See detailDerivation of flow and transport parameters from outcropping sediments of the Neogene aquifer, Belgium
Rogiers, Bart; Beerten, K.; Smeekens, T. et al

in Geologica Belgica (2013), 16(3), 129-147

Centimetre-scale saturated hydraulic conductivities (K) are derived from air permeability measurements on a selection of outcrops of the Neogene aquifer in the Campine area, Belgium. Outcrop sediments are ... [more ▼]

Centimetre-scale saturated hydraulic conductivities (K) are derived from air permeability measurements on a selection of outcrops of the Neogene aquifer in the Campine area, Belgium. Outcrop sediments are of Miocene to Quaternary age and have a marine to continental origin. Grain size analyses for the same outcrops and corresponding K predictions using previously developed models are also presented. We discuss outcrop hydrogeological properties and quantify the heterogeneity within the outcrops in detail using geostatistical variography. Moreover, outcrop-scale K values, their anisotropy and dispersivities are numerically calculated as a means to upscale such small-scale measurements to a larger scale commensurate with the scale of flow and transport modelling. By studying the small-scale variability as observed in outcrops, we gain crucial understanding of the larger-scale behaviour of the corresponding hydrogeological units within the Neogene aquifer, the most important groundwater reservoir of Flanders. The results of this study will equally improve conceptual hydrogeological model building and parameterization. [less ▲]

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See detailAssessing urbanisation effects on rainfall-runoff using a remote sensing supported modelling strategy
Verbeiren, Boud; Van de Voorde, Tim; Canters, Frank et al

in International Journal of Applied Earth Observation and Geoinformation (2013), 21

This paper aims at developing a methodology for assessing urban dynamics in urban catchments and the related impact on hydrology. Using a multi-temporal remote sensing supported hydrological modelling ... [more ▼]

This paper aims at developing a methodology for assessing urban dynamics in urban catchments and the related impact on hydrology. Using a multi-temporal remote sensing supported hydrological modelling approach an improved simulation of runoff for urban areas is targeted. A time-series of five medium resolution urban masks and corresponding sub-pixel sealed surface proportions maps was generated from Landsat and SPOT imagery. The consistency of the urban mask and sealed surface proportion timeseries was imposed through an urban change trajectory analysis. The physically based rainfall-runoff model WetSpa was successfully adapted for integration of remote sensing derived information of detailed urban land use and sealed surface characteristics. A first scenario compares the original land-use class based approach for hydrological parameterisation with a remote sensing sub-pixel based approach. A second scenario assesses the impact of urban growth on hydrology. Study area is the Tolka River basin in Dublin, Ireland. The grid-based approach of WetSpa enables an optimal use of the spatially distributed properties of remote sensing derived input. Though change trajectory analysis remains little used in urban studies it is shown to be of utmost importance in case of time series analysis. The analysis enabled to assign a rational trajectory to 99% of all pixels. The study showed that consistent remote sensing derived land-use maps are preferred over alternative sources (such as CORINE) to avoid over-estimation errors, interpretation inconsistencies and assure enough spatial detail for urban studies. Scenario 1 reveals that both the class and remote sensing sub-pixel based approaches are able to simulate discharges at the catchment outlet in an equally satisfactory way, but the sub-pixel approach yields considerably higher peak discharges. The result confirms the importance of detailed information on the sealed surface proportion for hydrological simulations in urbanised catchments. In addition a major advantage with respect to hydrological parameterisation using remote sensing is the fact that it is site- and period-specific. Regarding the assessment of the impact of urbanisation (scenario 2) the hydrological simulations revealed that the steady urban growth in the Tolka basin between 1988 and 2006 had a considerable impact on peak discharges. Additionally, the hydrological response is quicker as a result of urbanisation. Spatially distributed surface runoff maps identify the zones with high runoff production. It is evident that this type of information is important for urban water management and decision makers. The results of the remote sensing supported modelling approach do not only indicate increased volumes due to urbanisation, but also identifies the locations where the most relevant impacts took place. [less ▲]

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