The Effect of Bedform on Increasing The Flow Depth

Document Type : Research Article

Authors

1 Water Engineering Department, Agriculture Faculty, University of Tabriz, Tabriz-Iran

2 Department of Water Engineering, Faculty of Agriculture, University of Tabriz, Tabriz, Iran

3 Department of Water Engineering, Faculty of Agriculture, University of Tabriz, Tabriz-Iran

Abstract

Through sediment transport in alluvial channels, regular and alternating triangular-shaped patterns known as bedforms develop on the riverbed. Depending on the flow characteristics and regime, the geometric dimensions of these bedforms evolve, significantly influencing bed roughness and, consequently, increasing flow depth—particularly under ripple and dune conditions. Predicting flow depth based on bed roughness is therefore a critical aspect of hydraulic modeling and the design of hydraulic structures. In movable-bed channels, estimating flow resistance and its corresponding depth poses a major challenge due to the inherent uncertainty associated with the formation and transformation of bedforms. As such, developing a reliable, straightforward, and practical relationship to estimate the maximum flow stage in the presence of bedforms is both important and necessary. This study presents a simple and practical linear relationship for predicting flow stage under lower flow regime conditions, based on 292 recorded experimental cases from four reputable research sources. From this relationship, a coefficient of 1.25—referred to as the Tabriz University coefficient—is introduced, which significantly simplifies calculations of flow depth in the presence of ripple and dune bedforms without requiring detailed geometric information of the bedforms. The accuracy of this coefficient in estimating flow depth was found to be acceptable. Furthermore, a corresponding relationship for estimating the Manning roughness coefficient based on the flat-bed Manning coefficient was derived using this special coefficient. The performance of the proposed relationship for Manning’s coefficient was validated under controlled laboratory conditions in rectangular flumes. however, its application to natural channels remains outside the scope of this study and is suggested for future research.

Keywords

Main Subjects

References

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Amirkabir Journal of Civil Engineering
Volume 57, Issue 7
October 2025
Pages 1245-1264

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