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Swakopmund Desalination Plant EIA: Numerical Modelling Results

This EIA study presents numerical modelling results for the Swakopmund Desalination Plant, assessing potential environmental impacts of brine disposal and sediment impacts. The study includes assessments based on assumed project descriptions, limitations, and uncertainties. Input data from NCEP waves and bathymetry were used for detailed wave, hydrodynamic, brine discharge, and sediment transport model results. Findings focus on the intake and discharge pipe layouts, diffuser length, and other guidelines for the project.

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Swakopmund Desalination Plant EIA: Numerical Modelling Results

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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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