Stormwater Quality (SWQ)

Introduction

Stormwater Quality (SWQ) module applies surface pollution to catchment runoff. Surface pollution is specified as a special type of runoff model boundary condition with Water Quality (WQ) boundary properties specifying the quantities and dynamics of stormwater pollution.

SWQ supports separate definitions of stormwater pollution for fast surface runoff contributions and for slow RDI/NAM runoff contributions from catchments.

As any other catchment boundary condition, SWQ boundary condition can be spatially uniform (i.e. applied for all catchments) or spatially distributed (applied on a selection or individual catchment).

The following methods are supported for computation of stormwater water quality:

1. Simple concentration

2. Tabular concentration

3. Build-up/Wash-off

4. Event mean concentration (EMC)

Method 1 applies a concentration directly to the runoff from the catchment. The applied concentration can be specified as constant or cyclic or it can be based on an arbitrary time series. In this method, the concentration is independent of the runoff.

Method 2 applies a concentration of pollutant specified as a tabulated function of runoff intensity (i.e. specific runoff).

Note that Method 1 and Method 2 assume unlimited supply of pollutants on the catchment surface. These should be applied with care and only in appropriate cases.

Methods 3 and 4 simulate the build-up of pollutants or sediments on the catchment surface and wash-off of this pollution by mechanical action of rainfall. These methods are also referenced to as SWQ advanced methods.