Note: Comparison of the H2OMAP SWMM Hazen Williams Force Main Solution to a HW Solution
In this example, we compare the force main head loss in four links in H20Map SWMM to the head loss in a steady state HazenWilliams solution for the same length pipe, diameter and flow (Figure 1). The H2OMap SWMM model has a large constant dry weather inflow at the wet wells which floods the wet well and causes a constant pump flow to the force main (Figure 2). TheHW calculator is located here http://www.engineeringtoolbox.com/william-hazens-equation-d_645.html and a comparison forHW head loss in PSI for 5000 feet long, 3 inch diameter pipes with HW Coefficients of 130, 120, 110 and 100, respectively, is shown in Table 1. The SWMM 5 equation loss (PSI Diff) and the PSI loss from the HW calculator are very close for all four links.
Table 1. Steady State comparison between HW Calculator and H2OMAP SWMM/SWMM 5 Force Main calculations.
HW
|
SWMM5
|
SWMM5
|
SWMM5 Loss
|
Loss
|
Coefficient
|
Psi UP
|
PSI Dn
|
PSI Diff
|
PSI HW Calculator
|
130
|
84.563
|
44.88
|
39.683
|
39.82
|
120
|
88.772
|
43.765
|
45.007
|
45.16
|
110
|
91.798
|
41.426
|
50.372
|
50.54
|
100
|
95.354
|
38.727
|
56.627
|
56.82
|
Figure 1. H2OMAP SWMM Wet Well, Pump, Force Main and Gravity Main Network.
Figure 2. Constant Pump Flows
