Understanding SuDS design

Step-by-step:

Incorporating sustainable drainage systems – or SuDS – into a water drainage model can reduce flooding and improve water quality by reducing both flow rates and the amount of pollution carried to downstream watercourses.

For this exercise, it is useful to see how SuDS would fit into an existing drainage model, complete with pipes, a pond, and a discharge control point. Assume an outflow or discharge rate of 16.1 liters per second. Your goal is to place SuDS features in the catchment to control flow rates with the intention of being able to reduce the size of the pond. Open a drainage model file that requires SuDS.

1. In the Tree View, right-click the Pond design phase and select Duplicate Phase.
2. Click the light bulb icon next to the original Pond design phase to switch it OFF.
3. Click the green Go button to change it to a red Stop sign and stop further analysis on it.
4. Right-click the new Pond design (1) and select Rename Phase.
   

5. Type the name “SuDS design”.
6. Press ENTER.

All SuDS design will now take place within the new SuDS design phase.

7. In the Tree View, right-click the CAD Data node and select Import Data.
8. In the Load CAD Wizard, click Select.
9. In the Open dialog box, navigate to the file SuDS outline.dwg and open it.
10. In the Load CAD Wizard, click Next.
11. On the Select Layer page, click Deselect All.
12. Click the checkbox to enable only the ID_StormwaterControl layer.
13. Click Finish.

In the plan view, you can now see the imported outlines of a swale and permeable pavement area.

14. In the Tree View, deselect Inflows.

Now you can see how SuDS would fit into this existing drainage model.

Each SuDS structure will store water and include a flow limitation device to decrease the flow rates downstream so that the pond’s size can be reduced. In this example, there are some unknown variables, including the storage volumes of the SuDS features and the pass forward rates downstream of each. However, for now, assume that their storage volumes are fixed so that you can reduce the pass forward rates as much as possible. This allows you to reduce the size of the pond.