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

Project description • Provide numerical results to assess potential environmental impacts • Brine disposal 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

Conceptual layout of intake & discharge structures Conceptual layout of intake & discharge structures

Limitations and assumptions • Assessment based on project description as supplied • Uncertainties: Pipeline 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 (m 3/day) Brine Discharge Volumes (m 3/day) Intake Volumes (m 3/day) 80 000 90 000 170 000 Discharge Salinity (ppt) 65. 9 Increased Discharge Temperature (deg C) 1. 0

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

Input data: NCEP waves Input data: NCEP waves

Wave reliability NCEP vs Slangkop wave climate Annual Hmo exceedance: Slangkop (NCEP) 1% 5% 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)

Input data: bathymetry Input data: bathymetry

Model results: waves Model results: waves

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

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

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

Hydrodynamic modelling • Input requirements Wind, waves, offshore water temperature, surface heat fluxes (all Hydrodynamic modelling • Input requirements Wind, waves, offshore water temperature, surface heat fluxes (all concurrent) Bathymetry, beach profiles, D 50 • Calibration and verification data • Simulation periods Jan 2007 (summer) June 2007 (winter) Calm season (still to do)

Input data: Winds (NCEP) Input data: Winds (NCEP)

Model results: Currents Model results: Currents

Model results: Currents Model results: Currents

Near-field behaviours Near-field behaviours

Model results: Salinity (north option) Model results: Salinity (north option)

Model results: Salinity (south option) Model results: Salinity (south option)

Basin bathymetry Basin bathymetry

Suspended sediment transport Suspended sediment transport

Required information • Hydrodynamics: wind atmospheric data • Hydrodynamics: calibration data (ADCP) • Details Required information • Hydrodynamics: wind 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)

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

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