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Flushing to improve disinfectant residual

Dear all,

As a beginner, I would like to have a technical support on flushing to improve disinfectant residual in the network. First, I used a long term EPS-240 hr- water quality run using chlorine residual as the indicator of quality. The simulation shows that the most critical nodes of the network are the final ones in which the chlorine concentration is below the minimum  fixed (0.2 mg/l). Then I can use-as Dr. Tom Walski suggests- the ending values from this run as the beginning values for my flushing run. For the flushing flows of the critical nodes, do I have to assign them manually in the Demand section? Moreover, there is an automatic way to activate the flushing flows only when the chlorine residual falls below the minimum?

Thanks for any help and regards,

Stefania Avvedimento

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  • Hello Stefania,

    It looks like you're referring to this post from ten years ago. 

    For the flushing flows of the critical nodes, do I have to assign them manually in the Demand section?

    You must enter either the fixed demand outflow amount, or the emitter coefficient. There is some information here on determining the hydrant emitter coefficient, as well as the help topic "Estimating Hydrant Discharge using Flow Emitters". You don't necessarily need to do this for all flushing elements one by one though - you can enter it in the global flushing flows section (when clicking the flushing Area)

    Moreover, there is an automatic way to activate the flushing flows only when the chlorine residual falls below the minimum?

    After the Constituent run, you could set up a query to retrieve the nodes (or just hydrants) where the constituent statistical result is beyond your desired threshold, 

    ...then, in the Flushing tool (I assume you are using a recent version of WaterCAD or WaterGEMS), click New > New Conventional Events > click the lightning bolt dropdown and choose your selection set. This would then add all the desired nodes as conventional flushing nodes.


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

  • Note that my previous post assumed that you wanted to use the water quality run to identify hydrants to flush and that you want to use scour velocity as a criteria during the separate flushing run with the flushing tool.

    If you are wanting to flush the hydrants during the actual water quality run to see the impact it has on constituent concentration, you would need to use a standard constituent EPS run (like Dr. Walski talks about in the other forum discussion) and manually flush the hydrant. To answer your question, there isn't a way in this scenario, to automatically flush (apply a demand to) a hydrant based on a constituent concentration condition. One option may be to perform the long-term constituent run to see the locations where chlorine concentration is too low, then manually set up demand patterns to apply to those hydrants, with the demand pattern configuration to "open" (flush) the hydrant at the desired times (zero multiplier on the demand pattern except for the times when the hydrant will flush), then re-run the water quality EPS to see what impact the flushing would have.


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

  • The key here is to pick a flushing hydrant that you can flow without causing any flooding or discharging directly into a receiving stream.

    After you have raised the chlorine level, run a long term simulation to determine how long it will take for the chlorine concentration to degrade again. If the levels stay reasonably high, you can plan the flushing interval. If the levels drop off quickly, you may need to investigate the potential for installing a booster chlorine feed.

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  • The key here is to pick a flushing hydrant that you can flow without causing any flooding or discharging directly into a receiving stream.

    After you have raised the chlorine level, run a long term simulation to determine how long it will take for the chlorine concentration to degrade again. If the levels stay reasonably high, you can plan the flushing interval. If the levels drop off quickly, you may need to investigate the potential for installing a booster chlorine feed.

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