---
title: "Tutorial 6 - Modeling Stormwater Quality"
canonical: "https://help.innovyze.com/space/xps/19661371/Tutorial%206%20-%20Modeling%20Stormwater%20Quality"
format: markdown
---
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:

- Build-up of pollutants in catchments during dry periods
- Rate of pollutant wash off during storm events.

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](https://help-innovyze.atlassian.net/wiki/spaces/xps/pages/19661457). 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 × R**<sup>**exp**</sup>

where:

 C = concentration in runoff, mg/L

 Coeff = user defined washoff coefficient

 R = runoff flow, m<sup>3</sup>/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.

| **Level** | Intermediate |
| --- | --- |
| **Objectives** | - Define pollutant characteristics
- Define pollutant-land use buildup/wash off characteristics
- Simulate stormwater quality in simple catchment system |
| **Time** | 1 hour |
| **Data files** | **Yarra60m.xp** (starter file) |


1. Open the file *Yarra60m.xp *and set the Mode to **Rnf**.> Macro (inline-media-image)
2. Add **Landuse** records in the **Global Database** and define the pollutant buildup parameters for **Dust** and **Dirt**:
  1. From the **Configuration **menu, select **Global Data.**
  2. In the **Data Base Type** list, select **(R) Landuse**.
  3. Type the name **Forest **in the user field and then click **Add Record**.
  4. Select the **Forest** and click **Edit**.> Macro (inline-media-image)
  5. The default Dust and Dirt pollutant setting is **DD Limit** = **1E25 **and the **Buildup **rate is linear with **A **= **1**. This data is required for each land use record but is only used if the pollutant buildup option is **Landuse**. In that type of simulation, all pollutant buildup is tied to the buildup of dust and dirt as a fraction or factor. For this tutorial, set this data to default values and select **OK**. In this example, you will be defining pollutant wash off as ”None”.> Macro (inline-media-image)
  6. Repeat this step for land use types **Grassland** and **Residential**.   
> Macro (inline-media-image)
3. > Macro (anchor)

Define the parameters for each pollutant and each pollutant-land use combination according to the following table:  
> Macro (inline-media-image)
  1. From the **Configuration **menu, select **Global Data.**
  2. In the **Data Base Type** list, select **(R) Pollutant**.> Macro (inline-media-image)
  3. In the **Record Name**,** **select **TSS** and then click **Edit**. As shown below, enter the **Unit **label (**mg/l**) and the **Daily Decay Rate** (**0.0**) for **TSS**.> Macro (inline-media-image)
  4. Click the **Landuse specific data** button to define TSS’s pollutant’s wash off characteristics for each Landuse.
  5. Click the **Buildup/Washoff** button to open the **Buildup/Washoff** dialog.> Macro (inline-media-image)
  6. Add Records for **TSS-Forest**, **TSS-Grassland**, and **TSS-Residential** in the **Buildup/Washoff** characteristics.Select **TSS-Forest** in the left panel and then click **Edit**.> Macro (inline-media-image)
  7. For **Buildup,** select **None**. For **Washoff**, select **EMC**.  
> Macro (inline-media-image)
  8. <span style="color: #4a4a4a">Click </span><span style="color: #4a4a4a">**EMC**</span><span style="color: #4a4a4a">. Set the </span><span style="color: #4a4a4a">**Mean Concentration**</span><span style="color: #4a4a4a"> to </span><span style="color: #4a4a4a">**40**</span><span style="color: #4a4a4a">. Click </span><span style="color: #4a4a4a">**OK**</span><span style="color: #4a4a4a"> twice to return to the </span><span style="color: #4a4a4a">**Select**</span><span style="color: #4a4a4a"> dialog for </span>**<span style="color: #4a4a4a">Buildup/Washoff</span>**<span style="color: #4a4a4a"> and then click </span>**<span style="color: #4a4a4a">Select</span>**<span style="color: #4a4a4a"> to enter this record choice for the </span>**<span style="color: #4a4a4a">TSS-Forest</span>**<span style="color: #4a4a4a"> pollutant and landuse combination.</span>  
> Macro (inline-media-image)
  9. <span style="color: #4a4a4a">Repeat the input for the Buildup/Washoff data for </span>**<span style="color: #4a4a4a">TSS-Grassland</span>**<span style="color: #4a4a4a"> and </span>**<span style="color: #4a4a4a">TSS-Residential</span>**<span style="color: #4a4a4a">, following the table and the interim steps from major </span>[<span style="color: #4a4a4a">step 3</span>](#Tutorial6-ModelingStormwaterQuality-step3)<span style="color: #4a4a4a">.</span>
4. Add BOD buildup/washoff data:
  1. Repeat Steps 2 and 3 for pollutant **BOD**.
  2. Add **Buildup/Washoff **records for **BOD-Forest**, **BOD-Grassland**, and **BOD-Residential**.
  3. Set **Washoff** to **Rating Curve** and add the data for each BOD-landuse combination.> Macro (inline-media-image)
  4. Close all dialogs to return to the network view.
5. Set Runoff Job Control:
  1. In the **Configuration **menu, select **Job Control** **> Runoff**.
  2. Double-click the **Water Quality** button to launch the **Water Quality** dialog.
  3. Click the **Pollutant List** button.  
> Macro (inline-media-image)
  4. Select **TSS** and **BOD** from the **Pollutants** **list** and add them to the **Use Pollutants** list. Click **OK**.  
> Macro (inline-media-image)
  5. In the **Water Quality** dialog, select **Landuse List**. Add **Forest, Grassland,** and **Residential** to the **Use Land Uses** list. Click **OK**.  
> Macro (inline-media-image)
  6. Click **OK** to return to the network view.