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# Comparison of the H2OMAP SWMM5 Hazen Williams Force Main Solution to a HW Solution

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