Performance analysis of combined trapezoidal control notch in the sub-critical flow

Document Type : Research Paper

Authors

1 School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran

2 Department of Water and Environmental Engineering, School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran

3 Department of Civil Engineering, Faculty of Engineering, Urmia University, Urmia, Iran

Abstract

At the connection point of water conveyance canals carrying sub-critical flow with hydraulic structures such as inverted siphons and chutes, control notches can be used to create critical flow conditions and prevent water level drop in the downstream section or backwater flow in the upstream channel. In the present study, the performance of a combined trapezoidal control notch is investigated for the first time, and a method to determine its optimal dimensions for various discharges within the channel’s design discharge range is presented. For this purpose, the required equations are derived using specific energy equations and considering critical flow conditions over the notch and the non-linear equations are simultaneously solved using GRG method for discharges of 10, 25 and 50% of the design discharge. The obtained results are also validated through modeling in Flow3D software. Using this software, the flow characteristics including flow depth, specific energy, velocity profiles and stream lines over the proposed notch are evaluated. The results showed that the proposed structure is able to keep the flow in critical condition over different design discharges. The comparison between analytical results and the numerical method resulted in the proper compliance of these two methods with errors of less than 5%. Errors in flow depth ranged between 2.9% to 4.5%, and in specific energy 3.2% to 4.8%. The findings show that the use of a combined trapezoidal control notch creates critical flow conditions and prevents water level drop or backwater flow in the upstream channel under various hydraulic conditions.

Keywords

Main Subjects

Introduction

The existence of hydraulic structures such as chutes and spillways in water conveyance canals carrying sub-critical flow, sometimes leads to occurrence of high energy flow and excessive shear stress in the downstream section or backwater flow in the upstream section. Therefore, the presence of a water level regulator seems crucial. Typically, a trapezoidal weir with a crest level aligned with channel bed, which is called a trapezoidal control notch, is used to prevent water level drop or any erosion in canal. In some areas with variable hydraulic and hydrologic conditions, it is recommended to use combined sections to be able to handle very low flows to very high flows within the design discharge range. In this study, the specific energy method for designing control notches is used to design a combined trapezoidal control notch under various hydraulic conditions and its performance is investigated using Flow3D modeling software.

Method

In this study, a combined trapezoidal control notch is designed using the specific energy balance method under three different hydraulic conditions to regulate sub-critical flow in open channels. The structure consists of lower and upper sections with dimensions derived from critical flow equations. Numerical modeling was performed using Flow3D to investigate the performance of the structure. In other words, simulations validated water depth and specific energy against theoretical calculations. Design equations were solved using generalized reduced gradient method and the corresponding geometry was created in AutoCAD. This approach ensured critical flow maintenance without any backwater flow in the upstream section of the cannel.

Results

The combined trapezoidal control notch effectively maintained critical flow conditions across the tested discharge range (20–100% of design flow) for every hydraulic condition. Also, Flow3D simulations confirmed stable water depths upstream and specific energy, with less than 5% deviation from calculations. The structure prevented backflow and minimized water level fluctuations. The design demonstrated robustness in maintaining hydraulic efficiency under variable flow conditions.

Conclusions

This study indicated that the combined trapezoidal control notch effectively regulates subcritical flow while maintaining critical conditions across varying discharges. Numerical simulations validated the theoretical approach, showing desirable agreement with predicted hydraulic performance. These findings support the notch's practical application in water management systems requiring flow control.

Author Contributions

Conceptualization, R.Z. and A.M.; methodology, R.Z. and A.M.; software, A.M. and A.GH.; validation, A.M., R.Z. and A.GH.; formal analysis, A.M., R.Z. and A.GH.; investigation, A.M., R.Z. and A.GH.; writing—original draft preparation, A.M.; writing—review and editing, R.Z. and A.GH; visualization, A.M.; supervision, R.Z.

All authors have read and agreed to the published version of the manuscript

Data Availability Statement

Data is available on reasonable request from the authors.

Acknowledgements

The authors would like to thank all participants of the present study.

Ethical considerations

The authors avoided data fabrication, falsification, plagiarism, and misconduct.

Conflict of interest

 The authors declare no conflict of interest.

 

References

Ahadiyan, J., Abbasi Chenari, S., Azizi Nadian, H., Katopodis, C., Valipour, M., Sajjadi, S. M., & Omidvarinia, M. (2024). Sustainable systems engineering by CFD modeling of lateral intake flow with flexible gate operations to improve efficient water supply. International Journal of Sediment Research, 39(4), 629-642.
Arora, J. S. (2012). Introduction to optimum design. Lowa: Elsevier.
Askari, Z., Khodashenas, S. Z., Esmaili, K., Golian, M., Ostad-Ali-Askari, K., Singh, V. P. and Dalezios, N. R. (2019). Numerical analysis of hydraulic flow characteristics in prismatic compound channels using Flow3D software. American Research Journal of Civil and Structural Engineering, 3(1), 1-10.
Ayoob, N. S., Hamaad, A. M. (2022). Numerical simulation for flow over a broad-crested weir using Flow-3D program. Civil Engineering and Architecture, 10(5), 2157-2171.
Bayon, A., Valero, D., García-Bartual, R., Valles-Moran, F. J., Lopez-Jimenez P. A. (2016). Performance assessment of OpenFOAM and FLOW-3D in the numerical modeling of a low Reynolds number hydraulic jump. Environmental Modelling & Software, 80, 322-335.
Das, A. (2011). Critical channel dimensions for open-channel transition design. Journal of Irrigation and Drainage Engineering (ASCE), 137(11), 735-743.
Ghasemzadeh, F., & Kouchakzadeh, S. (2014). Design of trapezoidal flow measurement flume with crest level aligned with channel bed. Iranian Water Research Journal, 8(15), 1-10, (In Persian).
Ghasemzadeh, F., & Kouchakzadeh, S. (2023). Simulation of hydraulic problems in Flow3D. Third edition, Tehran: Noavar publishing company, (In Persian).
Hajialigol, S., Ahadiyan, J., Sajjadi, S. M., Hazi, M. A., Chadee, A. A., Nadian, H. A., & Kirby, J. T. (2024). Experimental analysis of turbulence measurements in a new dissipator structural (cross beams) in abruptly expanding channels. Results in Engineering, 21, 101829.
Karamdokht Behbahani, M., Sajjadi, S. M., Ahadiyan, J. (2024). Hydraulic investigation of the flow through multiple rectangular Lopac gate in free flow and submerged mode by Flow3D software, Iranian Journal of Irrigation and Water Engineering, 14(4), 19-32, (In Persian).
Kheybar, H., Sajjadi, S. M., & Ahadiyan, J. (2021). Effect of sudden canal contraction on the discharge coefficient and the energy dissipation coefficient of the elliptical LOPAC gate*. Irrigation and Drainage, 70(5), 1145-1154.
Kim, B. J., Hwang, J. H., Kim, B. (2022). Flow-3D model development for the analysis of the flow characteristics of downstream hydraulic structures. Sustainability, 14, 1-17.
Lee, J., Chan, H., Huang, C and Leu, J. (2012). Experiments on hydraulic relations for flow over a compound sharp-crested weir. International Journal of Physical Sciences, 7(14), 2229-2237.
Majedi-Asl, M., Jahanpeima, M., Khodapanah-Rad, P., Kouhdaragh, M., Bagherzadeh, M. (2023). Numerical investigation of flow over the rectangular compound sharp-crested weir at different angles in plan. Civil Infrastructure Researches, 9(2), 51-65, (In Persian).
Marosi, M., Roshan, R. & Sarkardeh, H. (2014). Analysis and design by Flow3D. First edition, Tehran: Fadakbook publishing company, (In Persian).
Mobarak, F., sajjadi, S. M., Ahadiyan, J., Zeynivand, M. (2022). Numerical modeling of the effect of elliptical elongation on the hydraulic performance of an elliptical Lopac gate, Water and Irrigation Management, 12(2), 263-275, (In Persian).
Mohammadi, M. & Vatankhah, A. (2020). Flow measurement flume with cylindrical and conical walls. Iranian Journal of Soil and Water Research, 51(7), 1637-1651, (In Persian).
Nouroozi, S., Ahadiyan, J. (2017). Effect of Vortex Breaker Blades 45 Degree on Discharge Coefficient of Morning Glory Spillway Using Flow-3D, Irrigation Sciences and Engineering, 40(1), 191-200, (In Persian).
Sarkamaryan, S. & Ahadiyan, J. (2020). Mathematical modeling of energy loss on Stepped Spillway Using ANSYS-CFX Numerical Model, Irrigation Sciences and Engineering, 43(1), 43-56, (In Persian).
Shahabi, M., Ahadiyan, J., Ghomeshi, M., Narimousa, M., Katopodis, C., & Nadian, H. A. (2022). Numerical study of the effect of a V-shaped weir on turbulence characteristics and velocity in V-weir fishways. River Research and Applications, 39(1), 21-34.
Shivapur, A., Mulangi, R., & Govardhan Swamy H. (2009). Use of inclined compound triangular notch-weir to improve discharge range, ISH Journal of Hydraulic Engineering, 15(3), 87-96.
Taghavi, M., Ghodousi, H. (2015). Simulation of flow suspended load in weirs by using Flow3D model. Civil Engineering Journal, 1(1), 37-49.
Taheri Talavari, T., Sajjadi, S.M., Ahadiyan, J. and Azizi Nadian, H., (2024). Numerical hydraulic and hydrodynamic investigation of flow passing through multiple elliptic lopac gates with Flow3D software. Advanced Technologies in Water Efficiency, 4(3), 40-60, (In Persian).
Vatankhah, A.R. (2013a). Limiting dimensions for trapezoidal channels and control notches (design aid). KSCE Journal of Civil Engineering, 17(4), 850-857.
Vatankhah, A.R. (2013b). Multiple critical depth occurrence in two-stage cross sections: effect of side slope change. Journal of Hydrologic Engineering (ASCE), 17(4), 850-857.
Waterbeheer, S. L. E. (2002). Design of open channels and hydraulic structures. Netherlands: TU Delft University.
       
Iranian Journal of Soil and Water Research
Volume 56, Issue 8
November 2025
Pages 2119-2136

Files

Share

How to cite

Statistics