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Thread: Function for open channel flow rate with input variable for inflow

  1. #1
    Associate Engineer
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    Apr 2017
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    Function for open channel flow rate with input variable for inflow

    Hello, I am conducting a research project which analyzes flow rates of open channels. In one particular portion of the project, I am analyzing an open channel that is receiving inflow from a separate source. Let us say for the purpose of this question that the flow rate of the water coming out from the separate source and into the open channel is entering the open channel with a flow rate of "Q" meters^3/sec. If this is the case, then once the water enters the open channel, will it continue to travel with the same flow rate "Q" regardless of the composition of the channel (ie. if the channel is earthen or if it is cemented)? Or instead, will the flow rate change? And if the flow rate changes, how will it change in accordance with the composition of the open channel? Finally, whatever the answer to this question maybe, how may I prove that answer mathematically and what equation would I use for such a proof?

    Please keep in mind that the water flow in the open channel is uniform, open channel flow.

    I have attempted to analyze this problem with the Manning formula. However, because the Manning formula does not offer a function input for inflow flow rate, I was unable to obtain an answer.

    Thank you very much.

  2. #2
    Lead Engineer
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    Aug 2013
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    Just as general consideration as long as the input flow rate is maintained then that flow rate "Q" will be maintained throughout the length of the channel; however, since it is an open channel, flow resistance can reduce the flow velocity in restricted regions or by accumulated flow friction by increasing the water depth as required to maintain sufficient water head pressure to overcome the drag resistance and maintain the required input flow rate "Q". Of course, if the channel is not of sufficient depth to provide the required head that is what we know as a flood condition.

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