Subject: Force Main Friction Loss in SWMM 5 You can model Force Mains in SWMM 5 using either Darcy Weisbach or Hazen Williams as the full pipe friction loss method (see Figure 1 for the internal defintion of full flow). No matter which method you use for full flow the program will use Manning’s equation to calculate the loss in the link when the link is not full (see Figure 2 for the equations used for calculating the friction loss – variable dq1 in SWMM 5). The regions for the different friction loss equations are shown in Figure 3.
|Figure 1. How the full pipe condition is defined in SWMM 5|
Figure 2: Friction equations used in SWMM 5 for a Force Main.