8/11/2019 Water Quality Modelling

1/1

Water Quality Modelling

Water quality models are used to analyse environmental systems and predict water quality changes due to

modifications in catchments and wastewater treatment plants. The prediction provides a basis for engineers to

carry out economic analysis to evaluate various options to improve the environment.

Water quality models are based on1) the law of conservation of mass (material transport into and out of the control volume as a physical process)

and

2) the change of substances in the control volume (transformation of the substances due to biological and/or

chemical processes). Material transport refers to the movement of the substances from one point to another,

which involves advection (movement with the fluid) and diffusion or dispersion (spread in the fluid due to

differences in concentration). The following water quality models are widely used:

AQUATOX - (Linking water quality and aquatic life) supported by EPA. This is a simulation model for aquatic

systems and is used to predict the fate of various pollutants, such as nutrients and organic chemicals, and their

effects on the ecosystem, including fish, invertebrates, and aquatic plants.

BASINS (Better Assessment Science Integrating point and Nonpoint Sources) supported by EPA. It is a multipurpose

environmental analysis system designed for watershed and water quality based studies. The software includes

the open-source MapWindow GIS interface, a Data Download Tool, project builder, watershed delineation

routines, and data analysis and model output visualisation tools. It also includes plug-in interfaces for well-known

watershed and water quality models SWMM5, WASP7, and SWAT 2005

QUAL2K -(River and Stream Water Quality Model ) supported by EPA. It covers one dimensional river channel with

conventional pollutants (nitrogen, phosphorus, dissolved oxy gen, BOD, sediment

Oxygen demand, algae), pH, periphy ton and pathogens.

SPARROW developed by USGS - a surface water-quality modelling tool for the regional interpretation of water-

quality monitoring data. The model relates in-stream water-quality measurements to spatially referenced

characteristics of catchments, including contaminant sources and factors influencing terrestrial and aquatic

transport. SPARROW empiricaly estimates the origin and fate of contaminants in river networks and quantifies

uncertainties in model predictions. The SPARROW model code is written in SAS Macro Language so it requires the

SAS (Statistical Analysis System Institute) software components.

SWMM (Storm Water Management Model (SWMM) supported by EPA. SWMM is a dynamic rainfall runoffsimulation model used for single event or long-term (continuous) simulation of runoff quantity and quality from

primarily urban areas. The runoff component of SWMM operates on a collection of subcatchment areas on which

rainfall-runoff is generated. The routing portion of SWMM transports this runoff through a conveyance system of

pipes, channels, storage/treatment devices, pumps, and regulators. SWMM tracks the quantity and quality of

runoff generated within each subcatchment, and the flow rate, flow depth, and quality of water in each pipe and

channel during a simulation period comprised of multiple time steps.

WASP (Water Quality Analysis Simulation Program) supported by EPA. This model helps users interpret and predict

water quality responses to natural phenomena and manmade pollution for various pollution management

decisions. WASP is a dynamic compartment-modelling program for aquatic systems, including both the water

column and the underlying benthos. The time varying processes of advection, dispersion, point and diffuse mass

loading and boundary exchange are represented in the model. WASP can be linked with hydrodynamic and

sediment transport models that can provide flows, depths velocities, temperature, salinity and sediment fluxes.