Water and Irrigation Management

Water and Irrigation Management

Validation of the Numerical Model for Submerged Flow Discharge Prediction Based on Experimental Measurements

Document Type : Research Paper

Authors
Bahare Rastipishe 1
Ali Salajegheh 1
younes aminpour 2
amirhossein parsamehr 3
1 Department of Arid and Mountainous Region Reclamation, Faculty of Natural Resources, University of Tehran, Karaj, Iran.
2 Hydraulic and Aquatic Environment Engineering Research Institute, Water Research Institute, Ministry of Energy, Tehran, Iran.
3 Department of Rangeland and Watershed Management (Nature Engineering), Faculty of Agriculture, Fasa University, Fasa, Iran.
10.22059/jwim.2026.411597.1291
Abstract
Accurate discharge measurement under submerged flow conditions remains a major challenge in irrigation and drainage networks. Portable SMBF flumes, despite their widespread application, experience reduced accuracy under submergence conditions. In this study, the hydraulic performance of an SMBF flume under submerged conditions was evaluated through an integrated experimental and numerical approach using the Flow-3D simulator. Experiments were conducted in a rectangular flume with contraction ratios of (r=0.342) and (r=0.561). In the numerical modeling framework, the RNG turbulence model and the Volume of Fluid (VOF) method were employed to accurately capture the free-surface dynamics. Model performance was assessed using RMSE, NSE, the Kling–Gupta Efficiency (KGE) index, and a systematic mesh sensitivity analysis. The results indicated that the contraction ratio (r=0.342) showed the best agreement with experimental data, while increasing the contraction ratio to (r=0.561) led to a reduction in model accuracy. Furthermore, an optimal grid configuration with a cell size of approximately one hundredth of a meter and a total number of cells between 105× 7/5 and 106×1/1 provided a suitable balance between numerical accuracy and computational cost. The main novelty of this study lies in presenting an integrated framework combining three-dimensional numerical modeling, mesh sensitivity analysis, and the application of the KGE index for multi-dimensional performance evaluation under submerged flow conditions. This approach enables simultaneous assessment of accuracy, stability, and variability of flow. The findings can be directly applied to the calibration of SMBF flumes and the improvement of discharge measurement accuracy in irrigation networks.
Keywords
Flow-3D
Kling–Gupta Efficiency (KGE)
Numerical modeling
SMBF flume
Subjects
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Water and Irrigation Management
Volume 16, Issue 1
Summer 2026
Pages 69-79