Predicting Discharge Coefficient of Rectangular Broad-Crested Gabion Weir Using M5 Tree Model

Research Paper


Currently made alternative structures from loose stones, gabion weirs are preferred with respect to solid concrete weirs formerly used in the past. By being more stable and flexible, gabion weirs have great advantage over their rigid (impervious) counterparts. The aim of this study was to investigate the overflow and through flow in rectangular broad-crested gabion weirs in order to evaluate the discharge coefficient C d. Eight physical models of broad-crested gabion weirs with four different porosities were made. The results of the experiments revealed that C d tended to be 20% less in submerged flow than in free flow. In addition, the average values of C d in both free and submerged flow were 0.66 and 0.53, respectively. Though increasing the gabion porosity led to an increase in C d, this amount became less and less with higher discharge values. M5 tree model as a sub-technique of data mining used to model C d values is capable of constructing tree-based piecewise linear equations for continuous datasets. The results showed that M5 tree model presents 12 linear equations for both free and submerged flows with R and RMSE of 0.95 and 0.036, respectively.


Broad-crested weir Discharge coefficient Gabion M5 tree model Porosity 



Weir width


Mean stone size used in gabion construction


Froude number = \(\frac{q}{{\sqrt g H_{1}^{1.5} }}\)


Acceleration due to gravity


Water depth in upstream of the weir measured from weir crest


Water depth in downstream of the weir measured from weir crest


Weir length


Porosity of gabion materials


Weir height




Discharge per unit width


Reynolds number


Submergence ration = H 2/H 1


Fluid density


Dynamic viscosity of the fluid (water)


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Copyright information

© Shiraz University 2017

Authors and Affiliations

  1. 1.Department of Water Engineering, Faculty of AgricultureUniversity of TabrizTabrizIran

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