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Swakopmund desalination plant EIA: Numerical modelling results Hardus Diedericks

Swakopmund desalination plant EIA: Numerical modelling results Hardus Diedericks. CSIR NATURAL RESOURCES AND THE ENVIRONMENT. Outline. Assumed project description Assumptions and limitations of the study Model results: waves, hydrodynamics, brine discharge and sediment transport

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Swakopmund desalination plant EIA: Numerical modelling results Hardus Diedericks

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  1. Swakopmund desalination plant EIA: Numerical modelling results Hardus Diedericks CSIR NATURAL RESOURCES AND THE ENVIRONMENT

  2. Outline • Assumed project description • Assumptions and limitations of the study • Model results: waves, hydrodynamics, • brine discharge and sediment transport • Additional requirements • Guidelines

  3. Project description • Provide numerical results to assess potential environmental impacts • Brine disposal at two possible intake/discharge pipe layouts • Sediment impacts at an intake basin • Results are for an EIA

  4. Conceptual layout of intake & discharge structures

  5. Limitations and assumptions • Assessment based on project description as supplied • Uncertainties: Pipeline locations, orientation, distance between intake and discharge pipes (parallel and perp.)

  6. Limitations and assumptions • Near-field behaviour based on conceptual designs, very near-field not resolved • Diffuser length 200 metres • 3D modelling needs improved input data and calibration data

  7. Input data: NCEP waves

  8. Wave reliability NCEP vs Slangkop wave climate Annual Hmo exceedance: Slangkop (NCEP) 1% 5% 10% 25% 50% 6.1 4.8 4.2 3.3 2.6 (5.7) (4.4) (3.8) (2.9) (2.3)

  9. Input data: bathymetry

  10. Model results: waves

  11. Wave applications • Waves are used in hydrodynamic simulations • (per month (season)) • Make a look-up table (rapid transformation) • (1997 – 2008)

  12. Waves at northern discharge position • Pipe orientation • approx 249o • Waves approx 225o • All waves

  13. Waves at locations (10 years) Northern location Southern location Proposed basin

  14. Hydrodynamic modelling • Input requirements • Wind, waves, offshore water temperature, • surface heat fluxes (all concurrent) • Bathymetry, beach profiles, D50 • Calibration and verification data • Simulation periods • Jan 2007 (summer) • June 2007 (winter) • Calm season (still to do)

  15. Input data: Winds (NCEP)

  16. Model results: Currents

  17. Model results: Currents

  18. Near-field behaviours

  19. Model results: Salinity (north option)

  20. Model results: Salinity (south option)

  21. Basin bathymetry

  22. Suspended sediment transport

  23. Required information • Hydrodynamics: wind and atmospheric data • Hydrodynamics: calibration data (ADCP) • Details of discharge and intake pipe locations • Chemical discharged (biocides) • Nearshore beach profiles at basin site • Median grain sizes (offshore and onshore)

  24. Analyses of results • Salinity, temperature, biocides and achievable dilutions • 80% to 99% exceedance contours • Days of exceedance of a selected guideline

  25. WQ Guidelines • Salinity (< 1 psu or < 36 psu; < 40 psu) • Temperature (ΔT < 1ºC; ANZECC) • Biocides (< 3 µg/ℓ) • Achievable Dilutions (nominally > 100)

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