Virtual Tutorial

The assessment criteria and guideline have been listed down in the EIAO-TM Annexes 6 and 14.

The generic approach in water quality assessment follows the sequence below:

• Scope water bodies in spatial and temporal extent, according to direct, indirect, near filed and far filed; and cumulative impacts of the Project;
  
• Identify pollution sources
  
• Identify water sensitive receivers
  
• Assess water quality impact
  
• Define mitigation measures
  
• Assess residual impact

Quantifying Water Quality Impact

There are different models for quantifying water quality impacts:

• Water Quality Model
  • Near Field - sewage/thermal, outfall initial dilution
    
  • Hydrodynamic - tidal flow modelling (currents and water levels)
    
  • Plume - sediment, bacterial, thermal
    
  • Water Quality - range of water quality parameters, establish pollution loading inventory
    
• Alternative Method
  
• Desktop mathematical calculation - suitable for assessing small dredging works by calculating depth averaged suspended sediment concentrations as a function of distance from works.

Some Tips¡K

When to Use Water Quality Modelling?

• Significant water quality concerns cannot be concluded by qualitative assessment
  
• Required by EIAO Study Brief(EIAO-TM Annexes 6 and 14)
  
• Potential for adverse water quality impacts
  
• Proximity to sensitive receivers
  
• Usually for discreet, quantifiable pollution sources
  
• Discharges exceeding the TM limits for Effluents
  
• Discharges into Drainage and Sewerage Systems Inland and Coastal Waters

When Not to Use Water Quality Modelling?

• Land based construction activities - controlled through specification of suitable control measures
  
• Very small scale cable laying - small scale sediment disturbance, sediment disturbance close to sea bed
  
• Very small scale dredging/reclamation works - subjective decision on not to model