Metric Tutorial Chapter 6 - Foul Design

Foul models are very similar to stormwater models, except inflow areas provide domestic and industrial flows, rather than rainfall runoff. Foul flows are steady state (do not change with time) and therefore foul design is much simpler than stormwater design as there is no volumetric analysis. Also, foul systems rarely include storage structures.

Foul models are built in the same way as stormwater models, by digitising the locations of manholes, pipes and inflow areas. In this exercise we will simply convert a stormwater model.

1. Open the file Foul Design.iddx
2. In the Tree View, right-click on the Storm Phase and switch it to a Foul system.
   
   
   An information message will appear.
   
   
   
3. Click OK. There are seven inflow areas in our catchment. We are going to assume that six of these areas each contain ten houses. Catchment Area 6 at the downstream end of the catchment is assumed to contain a small hospital and industrial unit.
4. Double-click the ‘Catchment Area’ inflow polygon in the north west of the catchment. It should open a dialog box of which only this part is relevant:
   
   
   We can see that there are three methods of assigning domestic flow:
   • Specifying a flow in l/s/ha and a peak flow factor.
   • Using the ‘main drainage’ calculation method, on the drop-down menu.
   • Using the ‘discharge unit’ calculation method, on the drop-down menu.
     
     
   We are going to use the main drainage method to represent the housing.
5. Ensure that the calculation method is set to main drainage .
6. Press on the little calculator buttonto see the default flow per dwelling values.
7. We are not going to edit these, so click OK.
8. Set the number of dwellings to 10.
   The resulting flow rate should be 0.4625 l/s.
   We could click on each of the inflow areas to change their characteristics, however it is perhaps easier to edit the values in a table.
9. Click OK to close the Catchment Area dialog.
10. From the Build menu, click Tables .
11. Click the little Inflows icon  in the top left corner of the tables.
12. Click the little + sign to expand the inflow headings.
13. Ensure that only five options are selected, as shown below.
    
    
    The resulting table should look like this. Note that you may need to close the table and re-open it, for the values to appear.
    
    
    
14. Change the calculation method and fill in the Flow per dwelling and the Number of dwellings for six out of seven catchments, as shown.
    
    
    
15. Click OK.
    We are now going to assign the hospital and industrial flows to the most downstream catchment.
16. Double-click the Catchment Area 6 polygon.
17. Tick on the industrial flow and set a value of 30 l/s/ha and an industrial peak flow factor of 2.00.
18. Ensure the calculation method is set to Discharge Unit.
    
    
    
19. Press on the little calculator button.
    Discharge units allow great flexibility in defining foul flows. The different system types allow for the assumption that say a wash basin in a hospital, would be used more than a wash basin in a house.
20. Ensure that the system is set to System I and fill in the number of appliances as follows:
    
    
    
21. Click OK.
22. Set the Frequency Factor to 1.0.
23. The resulting flow rate should be 14.18 l/s.
24. Click OK.
    We are now going to design the pipe network to serve these inflows.
25. Go to Preliminary sizing and Network design criteria.
26. Set up the design options as follows, noting that the design level and pipe full condition require editing.
    
    
    
27. Run the Network Design Wizard, clicking next when prompted.
    
    The network design report should look like this:
    
    
    The profile should look like this.