I'm using a Reservoir in WaterCad to model the connection point to an existing water main based on fire hydrant flow data.
This is a basic WaterCad question that has been discussed and it seems that everyone has a different opinion. I'm looking for insight on the use of a reservoir and fire flow test data to model the connection to an existing system using WaterCad. I'd like to confirm that this approach is valid along with the pros and cons of doing it this way. I do understand that you can use a pump curve to mimic the existing connection flow and pressure fluctuations. However; I'm only using a reservoir to model the connection.
The model was developed to evaluate fire flows required for a proposed multifamily development with a single looped 6" diameter water main.
Two hydrants were flow tested and the results are below:
FH-1 - Static PSI - 80, Residual PSI = 77, Pitot PSI = 62, Flow GPM = 3922
FH-2 - Static PSI - 80, Residual PSI = 72, Pitot PSI = 59, Flow GPM = 3826
Based on this data, I'm using 72 PSI and 3826 GPM to set the parameters for my reservoir.
Is this a valid approach? Pros and cons? Does the Pitot PSI need to be taken into account?
Any and all insight will be greatly appreciated!
Rob Wassum PE
Hello Rob,
I'm not sure if it was adjusted, you may need to check with the person or persons who did the hydrant test. If you know the discharge coefficient, you can use the equation that converts pitot pressure to flow to confirm if that was used. This is mentioned on page 185 (equation 5.1) of our book Advanced Water Distribution Modeling and Management. It's also referenced in this wiki article.
As far as the WaterCAD model, this would effect the inflow vs. pressure rating table that you establish with the "fake" pump and reservoir. As the downstream demand changes, the pump shifts on its curve to provide the corresponding pressure. If you're not seeing a significant pressure drop, then the exact flow amount from the recording may not have a large impact. You could also make a conservative assumption and use a reservoir at a fixed elevation.
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.