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HEC-HMS Unit Hydrograph generation problem

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  • O Mary
    Hello everyone, I am a new user of HEC-HMS and I can’t figure out the following problem: I have one rainfall gauge station on my study area (of about 30
    Message 1 of 3 , Mar 20, 2012
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      Hello everyone,

      I am a new
      user of HEC-HMS and I can’t figure out the following problem:
      I have one rainfall
      gauge station on my study area (of about 30 km2). The rain data is daily (i.e. one record per day).My
      flash flood spans for 12 days. I would want to generate the hydrograph on the
      basis of this rain data, using the Loss SCS Curve Number method and the SCS  Unit Hydrograph Transform method.  I determined the CN following the Purdue university
      tutorial, along with all the hydrologic parameters needed. I also determined
      the Basin Lag and the Time of Concentration according to the HEC HMS users’
      manual.
      My problem is that the
      hydrograph generated has values 10 to 15 times smaller than the streamflow measured
      data.
      I have no idea at all what do I am doing wrong, considering that a few months
      ago, on the same river basin, with the same  type of data, I managed to generate a
      hydrograph that fitted the measured streamflow hydrograph.
      Any
      suggestions would help a lot.

      Thanks,
      Mary
    • Alan A. Smith
      Hi Mary, A likely cause is a mix-up in the time-step being used. Rainfall data is depth per 24 hours and the hydrograph algorithm may be using 1-hour time
      Message 2 of 3 , Mar 20, 2012
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        Hi Mary,

        A likely cause is a mix-up in the time-step being
        used. Rainfall data is depth per 24 hours and
        the hydrograph algorithm may be using 1-hour time steps.
        As a last resort you might download MIDUSS from
        <www.miduss.com> (No cost) and use the Time
        Parameter, Storm, and Catchment commands. The
        latter can use the SCS CN to model runoff.

        Best of luck
        Alan A. Smith


        At 08:13 AM 20/03/2012, you wrote:
        >
        >Hello everyone,
        >
        >I am a new
        >user of HEC-HMS and I can’t figure out the following problem:
        >I have one rainfall
        >gauge station on my study area (of about 30
        >km2). The rain data is daily (i.e. one record per day).My
        >flash flood spans for 12 days. I would want to generate the hydrograph on the
        >basis of this rain data, using the Loss SCS
        >Curve Number method and the SCSÂ Unit
        >Hydrograph Transform method. Â I determined the
        >CN following the Purdue university
        >tutorial, along with all the hydrologic parameters needed. I also determined
        >the Basin Lag and the Time of Concentration according to the HEC HMS users’
        >manual.
        >My problem is that the
        >hydrograph generated has values 10 to 15 times
        >smaller than the streamflow measured
        >data.
        >I have no idea at all what do I am doing wrong, considering that a few months
        >ago, on the same river basin, with the same Â
        >type of data, I managed to generate a
        >hydrograph that fitted the measured streamflow hydrograph.
        >Any
        >suggestions would help a lot.
        >
        >Thanks,
        >Mary
      • Suresh Babu
        hi Mary, The first thing to check is your rainfall data. Is your rainfall data is representative enough for that event? Just do a quick check on volume
        Message 3 of 3 , Mar 20, 2012
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          hi Mary,

          The first thing to check is your rainfall data. Is your rainfall data is representative enough for that event? Just do a quick check on volume comparison between rainfall and runoff, assuming all rainfall becomes runoff, no loss. If your runoff/ rainfall ratio > 1, something wrong in rainfall data or not captured enough. If it is other way, need to look into it deeply.

          Cheers,
          Suresh

          Sent from my iPad

          On Mar 20, 2012, at 8:13 PM, O Mary <o.mary1234@...> wrote:

          > Hello everyone,
          >
          > I am a new
          > user of HEC-HMS and I can’t figure out the following problem:
          > I have one rainfall
          > gauge station on my study area (of about 30 km2). The rain data is daily (i.e. one record per day).My
          > flash flood spans for 12 days. I would want to generate the hydrograph on the
          > basis of this rain data, using the Loss SCS Curve Number method and the SCS Unit Hydrograph Transform method. I determined the CN following the Purdue university
          > tutorial, along with all the hydrologic parameters needed. I also determined
          > the Basin Lag and the Time of Concentration according to the HEC HMS users’
          > manual.
          > My problem is that the
          > hydrograph generated has values 10 to 15 times smaller than the streamflow measured
          > data.
          > I have no idea at all what do I am doing wrong, considering that a few months
          > ago, on the same river basin, with the same type of data, I managed to generate a
          > hydrograph that fitted the measured streamflow hydrograph.
          > Any
          > suggestions would help a lot.
          >
          > Thanks,
          > Mary
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