Experimental study of flow over trench weir with flat bars

Abstract

Trench weir is generally constructed across hilly streams to divert water for its use in multipurpose. Presented in this paper is experimental study of flow over trench weir with flat rack bars. Various factors affecting the discharging capacity are aspect ratio, rack slope, width of flat, clear spacing, and Reynolds number of the approach flow. Discharge equations are proposed for different flow conditions to compute the diverted discharge through the trench weir which compute the same within ±10% error. Since the trench is entirely filled with water for submerged flow condition, the jets flowing through the slits of the rack are no more subject to the atmospheric pressure and, hence, no air entrainment occurs and hence the diverted flow under submerged conditions is low with respect to free flow conditions. There is practically no loss of energy in the flow over the rack under the free and submerged flow conditions with partial withdrawal. Computed water surface profile over the rack compares well with the observed values. The flow in the trench is not unidirectional rather concentrated near the boundary of the trench outlet.

Keywords:

• Boulder stream
• discharge
• rack
• submergence
• trench weir

Acknowledgment

The authors are greatly thankful to Late Dr. U. C. Kothyari, Professor, IIT Roorkee for his direction and regular supervision as well as for providing required information about the results and also for his support in carrying out this research work.