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title: "(USA) Advanced Chapter 5 - Sizing of Treatment System"
canonical: "https://help.innovyze.com/space/infodrainage2020v2/16416816/(USA)%20Advanced%20Chapter%205%20-%20Sizing%20of%20Treatment%20System"
format: markdown
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Open the file **I****D_US_Advanced_Tutorial_Ch5.iddx** or continue working from your previous file.
You can carry on from the previous Tutorial or **switch **to the **Sizing of Treatment** Phase by selecting from the drop-down list on the left Tree View panel if you have not already done so.
There are three sizing components which are typically performed -** **[**runoff-reduction-sizing**](#id-(USA)AdvancedChapter5-SizingofTreatmentSystem-runoff-reduction-sizing), [**pond-protection-event-sizing**](#id-(USA)AdvancedChapter5-SizingofTreatmentSystem-pond-protection-event-sizing), and [**results-fine-tuning**](#id-(USA)AdvancedChapter5-SizingofTreatmentSystem-results-fine-tuning).
As you saw from reviewing the results, the treatment train is not currently configured to adequately and efficiently mitigate stormwater runoff from the site. The design aim is to capture and infiltrate 1 inch of the ‘first flush’ Runoff Reduction volume from the site, in order to address pollution concerns. Further, we must not discharge greater flow rates off site for the 5 and 100 year ARI events post-development than occurred in the pre-development (existing site) conditions. Select the desired component or work through all three starting with Runoff Reduction Sizing.
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Runoff Reduction Sizing
This chapter addresses the design aim to capture and infiltrate 1 inch of the ‘first flush’ Runoff Reduction volume from the site, in order to address pollution concerns.
1. First, you will size the system to address the Water Quality concerns by using a **Runoff Reduction** sizing calculator.
2. Edit **Raingarden** and select the **Sizing Calculator**** **button.
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3. There are several sizing methods that can be used to initially size Stormwater Control (SWC) facilities. In this tutorial, use the default **Runoff Reduction Volume** option. Further, there are several design levels which can be selected against which a facility can be adjusted. In this example, the default **Exceedence level** option will be used. Select the calculator icon within the **Sizing Calculator** dialog to assess Runoff Reduction volume.> Macro (inline-media-image)
4. There are several different options within the **Water Quality Volume** dialog. Select **Runoff Reduction** under **Method**, and **Use Plan Data** for **Input Type**. This will calculate the Runoff Reduction for all Inflow Areas connected to the SWC you are editing. Enter a **Precipitation Depth** of **1.0** inch and click **Calculate**.
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5. The calculated results will itemize the Inflow Volume required to be retained for all connected Inflow Areas as well as the current storage volume of the **Raingarden** SWC. Columns can be shown/hidden by selecting the options at the top of the dialog. Note that the current Outcome is Failure. The SWC could be upsized however space is tight on site and care must be taken to avoid the houses. Click **OK** to use this required volume to upsize the SWC and see the new outline.
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6. In the **Sizing Calculator**, the required retention volume is shown. There are several methods to update the facility, such as increasing the **Top** and **Bottom Areas** or making the facility deeper to accommodate the additional volume. The default **Areas** option should be selected, then click **OK** to update the SWC.
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7. The SWC dimensions will automatically adjust to accommodate the required Runoff Reduction Volume. Click **OK** to see the required footprint size of the SWC. > Macro (inline-media-image)
8. It is now much larger and may be overwhelmed in higher events. To ensure the smaller Bioretention area is not overwhelmed in higher events, one option is to split the **Inflow** into two areas, and use both the Raingarden and the Dry Pond facilities to retain and infiltrate the Runoff Reduction Volume. This also more accurately represents how the site will drain. Ensure that the **Snap** option is turned on under the **Plan** ribbon, then right-click the **Inflow Area** and select **Replace Outline > Free Form**.
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9. Trace the lower portion of the site area as shown, then press the **Esc** key to deselect the **Inflow**.> Macro (inline-media-image)
10. Create an **Inflow** for the remaining portion of the size as was done previously, select the **Urb-Res-Dev** template under **Build > Add Inflow**, as shown below.
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11. Notice that the newly added **Inflow Area** has been automatically connected to the adjacent **Standard MH **junction. No addition inlet specification or connection is needed.
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12. Press **Esc** to exit the drawing mode. Open the Raingarden again and rerun the **Sizing Calculator**, selecting **Runoff Reduction** again and the volume has now reduced. Update the Areas and the **Bioretention** now just fits into the space between the buildings. Further refinement may be needed in reality to ensure properties are not at risk however, this demonstrates the importance of being able to see the outline on plan.
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Pond and Protection Event Sizing
The controlling volume for the Dry Pond will be the 5 and 100 year ARI events, so no Runoff Reduction sizing is required for this facility, though the Sizing Calculator can be used to set an appropriate initial volume for the Dry Pond SWC to appropriately mitigate the larger runoff events.
1. Edit the **Dry Pond** SWC then select the **Sizing Calculator**, this time change the method to **Quick Storage Estimate** and the **Design Level** to **Freeboard**, this is to allow a 6 inch gap below the top level of the pond for safety.
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2. Click on the calculator next to the Volume and select the **Input Type** as **User Input,** to enable us to enter the whole area rather than only the directly connected portion. Enter the input as shown below. Select **SCS – Greenville** for the **Rainfall**, and then click **Calculate**.
- Area = **6.51 **ac
- Volumetric Runoff Coefficient = **0.9** – this is an approximation of the landuse defined within the Inflow Area
- Discharge Rate = **3.1** cfs – this is approximately the existing site discharge rate
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3. Due to the potential variance in rainfall events and runoff timing there is a wide approximate storage range indicated however the average will give us a good starting point. Click **OK** and note that an average volume for the potential range is selected.
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4. In the Sizing Calculator, change the **Design Level** to **Freeboard** to ensure that the Dry Pond is adjusted based on the storage below the Freeboard level.
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5. Click **OK** twice to see the initially sized top extents of the Dry Pond SWC.
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Results and Fine Tuning
1. Run the Analysis in order to compare results between the Existing and Developed Phases by selecting **Go** under the **Analysis** ribbon.
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2. After running the Analysis the **Stormwater Controls** summary is shown. Note that the first result shown is for the 1 in Water Quality Event, where there is no outflow from the Dry Pond, showing that all of the First Flush is completely retained within the site.
3. By changing the rainfall to the 100 year ARI event the **Raingarden** SWC is shown to Flood, while the Dry Pond is shown to have available (extra) volume capacity. > Macro (inline-media-image)
4. The view from the **Profile** shows slight overtopping of the Raingarden SWC. Use the **Playback Animation** toolbar to view the inundation across the system. Note the red horizontal lines indicate the Maximum Hydraulic Grade Line (HGL) for the elements within the system and the orange icon shown in the screenshot below indicates the Water Surface Level (WSL) is within the Freeboard for the SWC facility. > Macro (inline-media-image)
5. It is often easiest to calibrate the upstream facilities first in a multi-facility treatment train. Edit the **Raingarden ****SWC Weir** outlet, increase the width to 2 ft wide. Then run the analysis again.
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6. Viewing results for the Raingarden SWC for **All Storms** within the **Stormwater Controls** summary shows that increasing the weir width eliminated the flooding at this facility.
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7. Select **Comparison Report** under the **Results** ribbon, and use **Update Preview** to show a comparison between the Existing and Completed Design Phase outfall results.
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8. It is shown that the current Dry Pond outlet is discharging less flow than the Existing Phase. > Macro (inline-media-image)
9. You can continue to adjust the Treatment Train as discussed above in order to refine the Results comparison to the Existing Phase flows, if desired.
10. This tutorial in its entirety has been saved and can be viewed by opening the **ID_US_Advanced_Tutorial_Completed.iddx** file. The **Completed Design **phase can be opened to reference the final model configuration as described in the section above.> Macro (inline-media-image)
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11. The finished layout can be exported to AutoCAD file (*.dxg or *.dxf ). Go to the **Export** ribbon, and then select the **To CAD** button.
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