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Water quality

Method indicator
Bottom-Up Hybrid Top-Down

Summary of key issues:

Issue Description
Description Water quality modelling represents the advection and dispersion of suspended matter, dissolved oxygen and contaminants. Water quality models can also simulate the biochemical reactions that take place within biological systems such as nitrification and the decay of biological oxygen demand (BOD).
Temporal applicability Typically applied to the short to medium-term (single tide up to several months).
Spatial applicability Varying from a single point to estuary wide including the open coast.
Links with other tools Water quality modelling can be linked to various tools for the increased understanding of the impacts of water quality on biodiversity, for example.
Data sources
  • Typically, the qualitative models are not hydrodynamic dispersion models and require tidal information to drive the model.
  • Conservative substances (salinity, chloride, traces)
  • Decayable substances
  • Suspended sediment
  • Bacteria
  • Heavy Metals
  • BOD and COD (biological and chemical oxygen demand)
  • Algae
  • Oxygen
  • Temperature
  • Nutrients (ammonia, nitrate, phosphate, silicate)
  • Organic Matter (nitrogen, carbon, phosphorus, silicon)
Necessary software tools / skills Water quality models (typically linked to a hydrodynamic model); water quality expertise, thorough understanding of chemical processes occurring (e.g. biochemistry, flocculation).
Typical analyses The impact of discharge on any water body is dependent upon discharge quantity and the prevailing physical and chemical conditions.
Limitations Spatial extent of model determined from the knowledge of the location and temporal effect of the discharge. Calibration and validation of a water quality model should reflect the timescales of the parameters in question, tidal and possibly seasonal variability.


Water quality modelling solves the equation of advection-diffusion for a predefined computational grid on a wide range of model substances. Overall, water quality models aim to provide the user with information regarding the “condition” of a water body. Typically, water quality models require tidal information to drive the model.

The impact of a discharge on any water body is dependent on a discharge quantity and prevailing physical and chemical conditions. Typically, spatial and temporal conditions for each individual water bodies are highly variable. This is due to tidal and wind currents, bathymetry, fluvial flow. To asses the impact of a discharge it is necessary to predict the duration over which the pollutants may act and the area likely to be effected.

Read the full PDF document for more information on this methodPDF version

Analysis and modelling

Last Modified on: 19 June 2011
Printed from the Estuary Guide on 22/05/2024 09:13:28