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    On the efficiency of the hybrid and the exact second-order sampling formulations of the EnKF: a reality-inspired 3-D test case for estimating biodegradation rates of chlorinated hydrocarbons at the port of Rotterdam

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    Type
    Article
    Authors
    El Gharamti, Mohamad cc
    Valstar, Johan
    Janssen, Gijs
    Marsman, Annemieke
    Hoteit, Ibrahim cc
    KAUST Department
    Earth Fluid Modeling and Prediction Group
    Earth Science and Engineering Program
    Physical Science and Engineering (PSE) Division
    Date
    2016-11-15
    Permanent link to this record
    http://hdl.handle.net/10754/621918
    
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    Abstract
    This study considers the assimilation problem of subsurface contaminants at the port of Rotterdam in the Netherlands. It involves the estimation of solute concentrations and biodegradation rates of four different chlorinated solvents. We focus on assessing the efficiency of an adaptive hybrid ensemble Kalman filter and optimal interpolation (EnKF-OI) and the exact second-order sampling formulation (EnKFESOS) for mitigating the undersampling of the estimation and observation errors covariances, respectively. A multi-dimensional and multi-species reactive transport model is coupled to simulate the migration of contaminants within a Pleistocene aquifer layer located around 25 m below mean sea level. The biodegradation chain of chlorinated hydrocarbons starting from tetrachloroethene and ending with vinyl chloride is modeled under anaerobic environmental conditions for 5 decades. Yearly pseudo-concentration data are used to condition the forecast concentration and degradation rates in the presence of model and observational errors. Assimilation results demonstrate the robustness of the hybrid EnKF-OI, for accurately calibrating the uncertain biodegradation rates. When implemented serially, the adaptive hybrid EnKF-OI scheme efficiently adjusts the weights of the involved covariances for each individual measurement. The EnKFESOS is shown to maintain the parameter ensemble spread much better leading to more robust estimates of the states and parameters. On average, a well tuned hybrid EnKF-OI and the EnKFESOS respectively suggest around 48 and 21 % improved concentration estimates, as well as around 70 and 23 % improved anaerobic degradation rates, over the standard EnKF. Incorporating large uncertainties in the flow model degrades the accuracy of the estimates of all schemes. Given that the performance of the hybrid EnKF-OI depends on the quality of the background statistics, satisfactory results were obtained only when the uncertainty imposed on the background information is relatively moderate. © Author(s) 2016.
    Citation
    Gharamti ME, Valstar J, Janssen G, Marsman A, Hoteit I (2016) On the efficiency of the hybrid and the exact second-order sampling formulations of the EnKF: a reality-inspired 3-D test case for estimating biodegradation rates of chlorinated hydrocarbons at the port of Rotterdam. Hydrology and Earth System Sciences 20: 4561–4583. Available: http://dx.doi.org/10.5194/hess-20-4561-2016.
    Sponsors
    The authors would like to thank three anonymous reviewers for their constructive comments and suggestions, which improved the quality of the manuscript. The authors would also like to thank the municipality of Rotterdam for their support and cooperation throughout this project. Research reported in this publication was supported by King Abdullah University of Science and Technology (KAUST).
    Publisher
    Copernicus GmbH
    Journal
    Hydrology and Earth System Sciences
    DOI
    10.5194/hess-20-4561-2016
    Additional Links
    http://www.hydrol-earth-syst-sci.net/20/4561/2016/
    ae974a485f413a2113503eed53cd6c53
    10.5194/hess-20-4561-2016
    Scopus Count
    Collections
    Articles; Physical Science and Engineering (PSE) Division; Earth Science and Engineering Program

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