Introduction to the USTM

The mechanisms promoted in the removal of stormwater pollutants encompass physical, chemical and biological processes. Owing to the intermittent nature of stormwater inflow, physical processes associated with detention for sedimentation and filtration (either through vegetated systems or through an infiltration medium) are the principal mechanisms by which stormwater contaminants are first intercepted. Subsequent chemical and biological processes can influence the transformation of these contaminants.

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Two basic modelling procedures are adopted in the unified model - hydrologic routing to simulate the movement of water through the treatment system, and a first order kinetic model to simulate the removal of pollutants within the treatment system.

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