The water quality component may be added to a rainfall-runoff model to generate a time series of pollution concentration in the stormwater runoff. In XPSWMM/XPStorm, sub-catchment surface runoff to individual nodes is calculated in the Runoff mode (Rnf). When the water quality option is invoked, pollutographs are calculated for each contaminant at each active runoff node. These hydrographs and pollutographs may be stored on interface files that are input to the Sanitary mode (San) to model storage and treatment processes. The interface files may also be used as input to the Hydraulics mode (Hdr) to model the transport of contaminants through the network.
Modeling water quality in stormwater requires equations that describe the:
Typically, separate equations are developed for each pollutant-land use combination.
This tutorial demonstrates the simulation of total suspended solids (TSS) and biochemical oxygen demand (BOD) for the collection system developed in Tutorial 2 - Surface Water Hydrology. The pollutant build-up is not modeled. An infinite source is assumed to be available for wash off. Two wash off schemes are used. The TSS is modeled using the Event Mean Concentration (EMC) method. BOD is modeled with the rating curve:
C = Coeff × Rexp
C = concentration in runoff, mg/L
Coeff = user defined washoff coefficient
R = runoff flow, m3/s
exp = user defined exponent
The program has options for modeling Best Management Practices, such as street sweeping and pollutant removal in catch basins. The contaminant contributions from rainwater and groundwater can be simulated in Runoff mode. However, these advanced options are not included in this tutorial.
|Data files||Yarra60m.xp (starter file)|
Repeat this step for land use types Grassland and Residential.
For Buildup, select None. For Washoff, select EMC.
Click EMC. Set the Mean Concentration to 40. Click OK twice to return to the Select dialog for Buildup/Washoff and then click Select to enter this record choice for the TSS-Forest pollutant and landuse combination.
Set Runoff Job Control:
In the Configuration menu, select Job Control > Runoff.
Double-click the Water Quality button to launch the Water Quality dialog.
Click the Pollutant List button.
Select TSS and BOD from the Pollutants list and add them to the Use Pollutants list. Click OK.
In the Water Quality dialog, select Landuse List. Add Forest, Grassland, and Residential to the Use Land Uses list. Click OK.
Click OK to return to the network view.