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.

Figure 1.   H2OMAP SWMM Wet Well, Pump, Force Main and Gravity Main Network.

Figure 2.  Constant Pump Flows