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