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.)
Potable Water Produced
(m3/day)
Brine Discharge Volumes
Intake Volumes
Discharge Salinity
(ppt)
Increased Discharge Temperature
(deg C)
80 000
90 000
65.9
1.0

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% % % 25% %
(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)