Adjust for Elevation in Freeman Flow Equation?

Hi all, I am looking for a sanity check on a water supply calculation for water main with significant elevation delta.

We ran a hydrant test on a dead-end run for a new development that is fed from a city main at the top of a hill.

The two furthest hydrants were tested, the flow hydrant at the dead-end and pressure hydrant mid-way down the hill.

City Main = EL 500
Pressure Hydrant = EL 450
Flow Hydrant = EL 400
Proposed FFE = EL 425

The Freeman Flow equation bases hydrant flow on pitot pressure (PSIG) which is relative to the hydrant elevation. To calculate R20 (ie 20PSIG) at that hydrant elevation we use a ratio of PSIG values from the pressure hydrant normalized to 1.85 power multiplied by the hydrant flow rate from Freeman equation.

It is at this point that I begin second-guessing: the ratio that is being used does not take into account the elevation delta as it is PSIG. I have calculated the HGLs for the three pressures based on converting PSIG at its respective elevation.

My initial thought is that the pressure hydrant PSIGs (based on EL 450) should be converted to PSIGs at the flow hydrant (ie based on EL 400) by means of HGL - Hydrant Elevation and then using those "adjusted" PSIG static/residual values as the scaling terms for R20 at the flow hydrant. Then to get a theoretical R20 for a future hydrant at FFE I would repeat the same process, this time normalizing pressure hydrant static/residual HGLs to FFE elevation, holding the Freeman Flow value constant, and using a "new" R20 = 20PSIG at FFE.

​On the face I get reasonable values, but would like to get feedback from the group. Thanks in advance.

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