Optimizing a SuDS analysis

Step-by-step:

Once you have modeled a fully featured drainage system with SuDS, you are ready to simulate how they operate during rainfall events.

1. On the ribbon, Analysis tab, Analysis panel, click Validate.
2. In the Validate dialog box, verify there are no errors.
3. Close the dialog box.
4. On the ribbon, select Analysis Criteria.
   
5. In the Analysis Criteria dialog box, make sure the parameters are set as they appear in this example:
   
6. Click OK.
7. To run the analysis, on the ribbon, Analysis tab, Analysis panel, click Go.

Once the simulation is complete, the Stormwater Controls Summary dialog box opens. In this example, it shows the results of the first 15-minute summer storm. Realize that there are a total of 18 storms that were used throughout the creation of this model.

8. In the Stormwater Controls Summary, click Critical Storm to see how each stormwater control feature handles the most severe rainfall event.
   

In this example, three different storms were the critical duration for the three stormwater controls.

The Percentage Available (%) column shows the percentage of the total volume of the Stormwater Control available above the maximum water elevation measured to the exceedance elevation. A negative value shows that the capacity of the storage structure has been exceeded. Here, the pond has 39% of its capacity available. This is not surprising, because the introduction of the two SuDS structures to this model has reduced the flow rate into the pond. Now, you will be able to reduce its size substantially.

The swale is at minus 5%, meaning that it is a little undersized. However, the size of the swale is fixed, so instead, you need to increase the discharge rate from the swale so that its capacity is acceptable.

You can apply a similar approach to the cellular storage. It is currently at plus 8%, so its pass forward rate can be reduced a little.

Once you have optimized the upstream SuDS, you can reassess the pond.

Best practice is to create a new phase for the SuDS optimization:

9. In the Tree View, under the Phase Management node, right-click the SuDS design phase and select Duplicate Phase.
10. Right-click the new phase and click Rename Phase.
11. Rename it, “Optimized SuDS Design”.
12. Deactivate all other phases by toggling OFF the light bulb icons next to them, leaving the new phase as the only one visible.
13. Set all other phases to Stop, so that only the optimized suds design is set to Go.
    
14. Double-click the Cellular Storage icon to view its properties.
    
15. In the Cellular Storage dialog box, Outlets tab, open the Diameter Calculator.
16. Decrease the Design Flow to 7 liters per second.
17. Click OK.

Note that, back in the Cellular Storage dialog box, a new Diameter of 58 mm was calculated.

18. Double-click the Swale icon to open its properties.
    
19. In the Swale dialog box, Outlets tab, open the Diameter Calculator.
20. Increase the Design Flow (orifice flow) to 5.7 l/s.
21. The Diameter should have changed automatically to 52 mm. Click OK.
    
22. To run a simulation, in the ribbon, Analysis tab, Analysis panel, click Go.
23. When the Stormwater Controls Summary opens, click Critical Storm.
24. View the Percentage Available (%) column.

In this example, the swale and cellular storage capacities are now optimized to within 2% of capacity, but the pond is on 39% and therefore needs further optimization.

The Stormwater Controls Summary shows that the maximum resident volume in the pond is 485 meters cubed. A top tip is to size the pond slightly smaller than this value. In this case, it was determined that 385 meters cubed is the right size for the pond.

25. Double-click the Pond icon to open its properties.
    
26. Open the Sizing Calculator.
27. Enter a new Volume of 385 cubic meters.
    
28. In the Tree View, right-click Flow Paths and select Add.
29. Click manhole S1 to set the start point.
30. Click manhole S17 to set the endpoint.
    

In this example, the flow path reveals no broken connections.

31. Right-click the new flow path and select Show Profile to see the complete long section.
    
32. With the flow path still highlighted, on the ribbon, Analysis tab, Analysis panel, click Validate.
33. In the Validate dialog box, verify that there are no errors.
34. Click OK to close the dialog box.
35. On the ribbon, click Go to run the simulation.
    
36. In the Stormwater Controls Summary, click Critical Storm.
    
37. Review the Percentage Available (%) column.

There is zero percent available, but the Status is OK. The maximum resident volume is 384 meters cubed, so less than 1 meter cubed is available. In reality, you may need to increase the size of the pond slightly, but for this exercise, it is perfectly optimized.