J.M. Abril Department of Applied Physics (I); University of Seville (Spain) IAEA Regional Training Course on Sediment Core Dating Techniques. RAF7/008 Project J.M. Abril, University of Seville 1 Lecture 9: Case studies Spatial variability in sedimentation rates and radionuclide inventories. An approach from Computational Fluid Dynamics Models Irish Sea and Härsvatten lake

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Horizontal movement, with water velocity Settling velocity Resuspension BASIC PROCESSES FOR SPM DYNAMICS AND SEDIMENTATION RATES J.M. Abril, University of Seville 3

Bathimetry The Irish Sea J.M. Abril, University of Seville 4

Distribution (in % dry weight) of small particles (ф ≤ 62.5 µm) in the top sediment layer for the Irish Sea. J.M. Abril, University of Seville 5

Residual circulation Stream function (km 3 y -1 ) calibrated by modelling the salinity distribution J.M. Abril, University of Seville 6

SOURCE TERM: Proportional to freshwater discharges along the shoreline SOURCE TERM: Proportional to freshwater discharges along the shoreline J.M. Abril, University of Seville 7

SEDIMENTATION RATES arise as net balance of deposition and resuspension or, alternatively, as a mass balance at each grid-cell J.M. Abril, University of Seville 8

The grid used in our numerical model, with grid lengths Δx = Δy = 5.16 km. Numbers in the X and Y directions are the index used to label each grid- cell. Black boxes represent land and the white ones water. Eq. 1 is solved in the center of each grid-cell at every time step. J.M. Abril, University of Seville 9

Modelling the mean annual SALINITY distribution served to calibrate the diffusion term in the transport equation Observed Model J.M. Abril, University of Seville 10

Estimated river discharges (km 3 y -1 ) for each coastal sector (defined between arrows) taken from MAFF (MAFF, 1987). Contours (x 10 3 km 3 over each compartment) represent computed steady-state distribution of volumes from these river discharges. J.M. Abril, University of Seville 11

Computed steady-state spatial distributions of SPM and sedimentation rates J.M. Abril, University of Seville 12

VALIDATION SPM (a) and net deposition (b) vs. distance from the Cumbrian coast-line. Circles are measured values. SENSITIVY TEST: The continuous line is for our selected set of parameter values. The dashed and point dashed lines corresponds to double and a half value of settling velocity. J.M. Abril, University of Seville 13

All these results for w confirm the general accepted impression about the sedimentary processes taking place at the Irish Sea. IOS and MAFF (Kirby et al., 1983) did not found evidences of net erosion nor sedimentation in the mud bank of Cumbria, concluding that the sedimentary regime in this area is relatively stable. J.M. Abril, University of Seville 14

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The model solves the three dimensional hydrodynamic equations, using normalized σ coordinates in the vertical It includes wave–current interaction through by an increase in the current friction factor, J.M. Abril, University of Seville 17

Suspended matter equations m s is the SPM concentration, and w s is their settling velocity Deposition and erosion of the sediment are incorporated into the sea bed boundary condition. Both processes have threshold velocities. E is the erodability, M (2-5) is some power of the water velocity, and f gives the fraction of particles with a diameter <62.5 lm in the sediment Includes a source term, as in Abril and García-León, J.M. Abril, University of Seville 18

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Lake Härsvatten J.M. Abril, University of Seville 22

Large-scale and Long-term Environmental Behaviour of Transuranic Elements as Modelled through European Surface Water Systems. This work is part of a research project financially supported by the European Commission, Nuclear Fission Safety Programme, Contract No. FI4P-CT (DG12-WSMN ). Coordinator: Dr. F. El-Daoushy (Uppsala University, Sweden). Partners: Dr. F. El-Daoushy (Uppsala University, Sweden) Prof. P. G. Appleby (University of Liverpool, the United Kingdom); Prof. M. García-León (Universidad de Sevilla, Spain); Dr. P. Casper (Forschungsverbund Berlin e.V.-Gemeinsame Verwaltung, Germany); Prof. G. Ardisson (Université de Nice, France). J.M. Abril, University of Seville 23

In radioecology, lakes have often been considered as well mixed water bodies From CFD studies we know that the magnitude of the wind forced water currents is of the order of some cm/min to few cm/s over spatial scales of the order of few kilometers. Consequently, the time scale involved in the dispersion and mixing of any input of pollutants will be, typically, of several days or weeks, being the lacustrine system comparable to an estuarine or a coastal areas with length-scales of ten or hundred kilometers and with water currents of the order of 1 m/s. Thus, the spatial distribution of concentrations and inventories or the focussing, cannot be properly understood without considering the hydrodynamics of the lacustrine water body. J.M. Abril, University of Seville 24

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Focusing ? J.M. Abril, University of Seville 26

Bathymetric map and grid for numerical model J.M. Abril, University of Seville 27

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Advective tracks J.M. Abril, University of Seville 33 Vs

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Spheroidal carbonaceous fly-ash particles R. Bindler et al. Spatial distribution of SPC inventories by quartiles J.M. Abril, University of Seville 37

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J.M. Abril, University of Seville 39 Modelling SPM dynamics

J.M. Abril, University of Seville 40 Modelling sedimentation rates

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Pu concentrations in dissolved phase (a.u.) 24 after a hypothetical atmospheric input. Spatial distribution of SPC inventories by quartiles J.M. Abril, University of Seville 43

The present model development has to be understood as an effort to produce a suitable virtual laboratory for testing our knowledge on radionuclide behaviour in lake systems and lacustrine sediments, being at time like a map to assist future research in this field J.M. Abril, University of Seville 44