Ingeborg Joris

LPMLE3: A novel 1‐D approach to study water flow in streambeds using heat as a tracer

We introduce LPMLE3, a new 1-D approach to quantify vertical water flow components at streambeds using temperature data collected in different depths. LPMLE3 solves the partial differential equation for coupled water flow and heat transport in the frequency domain. Unlike other 1-D approaches it does not assume a semi-infinite halfspace with the location of the lower boundary condition approaching infinity. Instead, it uses local upper and lower boundary conditions. As such, the streambed can be divided into finite subdomains bound at the top and bottom by a temperature-time series. Information from a third temperature sensor within each subdomain is then used for parameter estimation. LPMLE3 applies a low order local polynomial to separate periodic and transient parts (including the noise contributions) of a temperature-time series and calculates the frequency response of each subdomain to a known temperature input at the streambed top. A maximum-likelihood estimator is used to estimate the vertical component of water flow, thermal diffusivity, and their uncertainties for each streambed subdomain and provides information regarding model quality. We tested the method on synthetic temperature data generated with the numerical model STRIVE and demonstrate how the vertical flow component can be quantified for field data collected in a Belgian stream. We show that by using the results in additional analyses, nonvertical flow components could be identified and by making certain assumptions they could be quantified for each subdomain. LPMLE3 performed well on both simulated and field data and can be considered a valuable addition to the existing 1-D methods.

The addition of organic carbon and nitrate affects reactive transport of heavy metals in sandy aquifers

Organic carbon introduction in the soil to initiate remedial measures, nitrate infiltration due to agricultural practices or sulphate intrusion owing to industrial usage can influence the redox conditions and pH, thus affecting the mobility of heavy metals in soil and groundwater. This study reports the fate of Zn and Cd in sandy aquifers under a variety of plausible in-situ redox conditions that were induced by introduction of carbon and various electron acceptors in column experiments. Up to 100% Zn and Cd removal (from the liquid phase) was observed in all the four columns, however the mechanisms were different. Metal removal in column K1 (containing sulphate), was attributed to biological sulphate reduction and subsequent metal precipitation (as sulphides). In the presence of both nitrate and sulphate (K2), the former dominated the process, precipitating the heavy metals as hydroxides and/or carbonates. In the presence of sulphate, nitrate and supplemental iron (Fe(OH)(3)) (K3), metal removal was also due to precipitation as hydroxides and/or carbonates. In abiotic column, K4, (with supplemental iron (Fe(OH)(3)), but no nitrate), cation exchange with soil led to metal removal. The results obtained were modeled using the reactive transport model PHREEQC-2 to elucidate governing processes and to evaluate scenarios of organic carbon, sulphate and nitrate inputs.

Model-based Scenario Analysis of the Impact of Remediation Measures on Metal Leaching from Soils Contaminated by Historic Smelter Emissions

A spatially distributed model for leaching of Cd from the unsaturated zone was developed for the Belgian-Dutch transnational Kempen region. The model uses as input land-use maps, atmospheric deposition data, and soil data and is part of a larger regional model that simulates transport of Cd in soil, groundwater, and surface water. A new method for deriving deposition from multiple sites was validated using soil data in different wind directions. Leaching was calculated for the period 1890 to 2010 using a reconstruction of metal loads in the region. The model was able to reproduce spatial patterns of concentrations in soil and groundwater and predicted the concentration in shallow groundwater adequately well for the purpose of evaluating management options. For 42% of the data points, measurements and calculations were within the same concentration class. The model was used for forecasting under a reference scenario, an autonomous development scenario including climate change, and a scenario with implementation of remediation measures. The impact of autonomous development (under the most extreme scenario of climatic change) amounted to an increase of 10% in cumulative Cd flux after 100 yr as compared with the reference scenario. The impact of remediation measures was mainly local and is less pronounced (i.e., only 3% change in cumulative flux at the regional scale). The integrated model served as a tool to assist in developing management strategies and prioritization of remediation of the wide-spread heavy metal contamination in the region.

Examples of Risk Management in Flanders for Large Scale Groundwater Contamination

With respect to soil and groundwater remediation in Flanders, regulators have recently adopted a new, risk-based, policy. This policy is illustrated by two examples of risk management applied for large scale ground-water contamination. The first case involves a benzene and MTBE groundwater contamination threatening a shallow drinking water production site. Source zone treatment combined with pump & treat plume interception may be the only risk-based remediation strategy applicable in such cases. The second example is a risk management plan designed for the redevelopment of a brownfield located near Brussels, Belgium. In this area, an extensive ground-water contamination of monoaromatic and chlorinated aliphatic hydrocarbons is present in the Quaternary aquifer drained by the river Zenne. The risk management plan involves the combination of intensive treatment of source zones and plume treatment.

Quasi 3D modelling of vadose zone soil-water flow for optimizing irrigation strategies: Challenges, uncertainties and efficiencies

Abstract A quasi 3D modelling approach was developed by integrating a crop growth (LINGRA-N) and a hydrological model (Hydrus-1D) to simulate and visualize water flow, soil-water storage, water stress and crop yield over a heterogeneous sandy field. We assessed computational efficiency and uncertainty with low-to high-spatial resolution input factors (soil-hydraulic properties, soil-layer thickness and groundwater level) and evaluated four irrigation scenarios (no, current, optimized and triggered) to find the optimal and cost-effective irrigation scheduling. Numerical results showed that the simulation uncertainty was reduced when using the high-resolution information while a fast performance was maintained. The approach accurately determined the field scale irrigation requirements, taking into account spatial variations of input information. Optimal irrigation scheduling is obtained by triggered-irrigation resulting in saving up to ∼300% water as compared to the current-irrigation, while yield increased ∼1%. Overall, the approach can be useful to help decision makers and applicants in precision farming.

Bodemverdichting in Vlaanderen : Gevolgen van bodemverdichting op het watertransport door een bodem

De gevolgen van bodemverdichting op het watertransport door een bodem zijn verkend. Een bodemfysische database is gecreeerd door naast historische metingen nieuwe metingen te verzamelen op verdichte percelen. Dat is gebeurd door op 26 percelen op 2 plekken op 3 diepten ongestoorde monsters te nemen en de bodemfysische eigenschappen te bepalen. Op 6 percelen zijn continue hydrologische metingen verricht van bodemvocht op 3 diepten en grondwaterstanden. De laatste metingen zijn gebruikt om te toetsen of het model SWAP met de gemeten bodemfysische eigenschappen in staat is het watertransport in het perceel te beschrijven. Met SWAP zijn voor 5 Vlaamse stroomgebiedjes de effecten van bodemverdichting verkend voor klimaatscenario’s door de verdichte en niet-verdichte toestand te vergelijken. De met de pedotransferfuncties en nieuwe data berekende effecten van verdere verdichting op de waterhuishouding blijken globaal gezien beperkt te zijn. Dit neemt niet weg dat de lokale effecten mogelijk aanzienlijk kunnen zijn, gelet op de grote variatie in bodemverdichting die binnen de percelen werd opgemeten. De verschillen tussen de verdichte en niet-verdichte situatie in stroomgebieden zijn beperkt. Klimaatscenario’s leiden op verdichte bodems tot meer oppervlakkige afstroming en meer droogtegevoeligheid

LPMLE3 : A New Analytical Approach to Determine Vertical Groundwater-Surface Water Exchange Flux under Uncertainty and Heterogeneity

(1) VITO, Environmental Modeling Unit, Mol, Belgium (uwe.schneidewind@vito.be), (2) Ghent University, Department of Soil Management, Gent, Belgium, (3) Eindhoven University of Technology, Department of Mechanical Engineering, Eindhoven, The Netherlands, (4) FOM Institute DIFFER, Dutch Institute for Fundamental Energy Research, Nieuwegein, The Netherlands , (5) VUB Vrije Universiteit Brussel, Department of Hydrology and Hydraulic Engineering, Brussels, Belgium, (6) VUB Vrije Universiteit Brussel, Department of Fundamental Electricity and Instrumentation, Brussels, Belgium, (7) University of Antwerp, Department of Bioscience Engineering, Antwerp, Belgium, (8) Flinders University, School of the Environment, Adelaide, Australia

Determining Groundwater-Surface Water Exchange Fluxes and Their Spatial Variability Using the Local Polynomial Method LPML

(1) VITO, Environmental Modeling Unit, Mol, Belgium (uwe.schneidewind@vito.be), (2) Ghent University, Department of Soil Management, Ghent, Belgium, (3) VUB Vrije Universiteit Brussel, Department of Hydrology and Hydraulic Engineering, Brussels, Belgium, (4) VUB Vrije Universiteit Brussel, Department of Fundamental Electricity and Instrumentation, Brussels, Belgium, (5) University of Antwerp, Department of Bioscience Engineering, Antwerp, Belgium, (6) Flinders University, National Centre for Groundwater Research and Training, School of the Environment, Adelaide, SA, Australia

Application of Interval Fields for Uncertainty Modeling in a Geohydrological Case

In situ soil remediation requires a good knowledge about the processes that occur in the subsurface. Groundwater transport models are needed to predict the flow of contaminants. Such a model must contain information on the material layers. This information is obtained from in situ point measurements which are costly and thus limited in number. The overall model is thus characterised by uncertainty. This uncertainty has a spatial character, i.e. the value of an uncertain parameter can vary based on the location in the model itself. In other words the uncertain parameter is non-uniform throughout the model. On the other hand the uncertain parameter does have some spatial dependency, i.e. the particular value of the uncertainty in one location is not totally independent of its value in a location adjacent to it. To deal with such uncertainties the authors have developed the concept of interval fields. The main advantage of the interval field is its ability to represent a field uncertainty in two separate entities: one to represent the uncertainty and one to represent the spatial dependency. The main focus of the paper is on the application of interval fields to a geohydrological problem. The uncertainty taken into account is the material layers’ hydraulic conductivity. The results presented are the uncertainties on the contaminant’s concentration near a river. The second objective of the paper is to define an input uncertainty elasticity of the output. In other words, identify the locations in the model, whose uncertainties influence the uncertainty on the output the most. Such a quantity will indicate where to perform additional in situ point measurements to reduce the uncertainty on the output the most.