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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 19, issue 10
Hydrol. Earth Syst. Sci., 19, 4041–4053, 2015
https://doi.org/10.5194/hess-19-4041-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Hydrol. Earth Syst. Sci., 19, 4041–4053, 2015
https://doi.org/10.5194/hess-19-4041-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 05 Oct 2015

Research article | 05 Oct 2015

A methodological approach of estimating resistance to flow under unsteady flow conditions

M. M. Mrokowska, P. M. Rowiński, and M. B. Kalinowska M. M. Mrokowska et al.
  • Institute of Geophysics Polish Academy of Sciences, Ks. Janusza 64, 01-452 Warsaw, Poland

Abstract. This paper presents an evaluation and analysis of resistance parameters: friction slope, friction velocity and Manning coefficient in unsteady flow. The methodology to enhance the evaluation of resistance by relations derived from flow equations is proposed. The main points of the methodology are (1) to choose a resistance relation with regard to a shape of a channel and (2) type of wave, (3) to choose an appropriate method to evaluate slope of water depth, and (4) to assess the uncertainty of result. In addition to a critical analysis of existing methods, new approaches are presented: formulae for resistance parameters for a trapezoidal channel, and a translation method instead of Jones' formula to evaluate the gradient of flow depth. Measurements obtained from artificial dam-break flood waves in a small lowland watercourse have made it possible to apply the method and to analyse to what extent resistance parameters vary in unsteady flow. The study demonstrates that results of friction slope and friction velocity are more sensitive to applying simplified formulae than the Manning coefficient (n). n is adequate as a flood routing parameter but may be misleading when information on trend of resistance with flow rate is crucial. Then friction slope or friction velocity seems to be better choice.

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This paper presents evaluation of resistance parameters: friction slope, friction velocity and Manning coefficient in unsteady flow. Theoretical description is facilitated with the analysis of field data from artificial dam-break flood waves in a small lowland watercourse. The methodology to enhance the evaluation of resistance by relations derived from flow equations is proposed. The study shows the Manning coefficient is less sensitive to simplified relations than other parameters.
This paper presents evaluation of resistance parameters: friction slope, friction velocity and...
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