Discussion of “Unsteady Stage-Discharge Relationships for Sharp-Crested Weirs” by Firouz Ghasemzadeh, Salah Kouchakzadeh, and Gilles Belaud.

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I would like to thank the authors for writing this interesting articledealing with unsteady stage-discharge relationships for sharp-crestedweirs. The operation of triangular and rectangular sharp-crestedweirs in unsteady flow conditions was experimentally investigated.Results indicated the presence of looped rating curves, with transpositionof the rising and falling limbs compared to that commonlyobserved in stream gauge ratings. The authors found that thedeviation between steady and unsteady flow rates in the looped ratingcurves depends on the weir type and the hydrograph gradient(i.e., the temporal depth variation), especially when the latterchanges rapidly.Finally, they proposed calibrated relationships, where two empiricalcoefficients account for the so-called hydrograph equivalentslope defined as the geometric mean of the absolute slope value ofthe water head above the weir crest, between the rising and the fallinglimb, which incorporates the effect of flow unsteadiness.For a circular sharp-crested orifice at the bottom of a tank, theunsteady stage-discharge relationship, only differing in the exponentx of the water level, h, above the crested orifice (x ¼ 1=2 forcircular holes, x ¼ 3=2 for rectangular weirs, x ¼ 5=2 for triangularweirs), was recently derived (Baiamonte 2020a, b). The onlyobjective of this discussion is to show that the deviation betweensteady and unsteady flow rates in the looped rating curves could beanalytically derived without calibration. As a consequence, the effectof the average hydrograph gradient found by the authors can beanalytically determined for both the rising and the falling limbs. Theanalysis is performed for dimensionless groups, which makes theresults more general and more useful for their ability to contract,or make more succinct, the functional form of physical relationships.
Lingua originaleEnglish
Numero di pagine3
Stato di pubblicazionePublished - 2021

All Science Journal Classification (ASJC) codes

  • ???subjectarea.asjc.2200.2205???
  • ???subjectarea.asjc.2300.2312???
  • ???subjectarea.asjc.1100.1101???


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