Experimental investigation of a trench weir with T-shaped bars

Abstract

The most common type of diversion structure used in boulder streams is a trench weir. It is a simple structure built below the bed level of streams, and the top of it is covered with bottom rack. Bottom rack consists of bars of various shapes like circular, rectangle, T-shaped, etc. It is placed over the trench weir with a desired porosity to control sediment ingestion into trench. In this present study, T-shaped bars are used because sediment ingestion and maintenance in the bottom rack consisting of T-shaped bar shall likely too low as compared to the rounded bars and rectangular bars. As in previous studies, Garcia et al. (Water 10(1035):1–21, 2018a, Water 10(1699):1–21, 2018b) compared the blocking capacity of bottom intakes having circular bars with intakes having T-shaped bars, they claimed that circular bar is inefficient as compared to T-shaped bars. The present study is based on experimental investigation of trench weir consisting of T-shaped bars under free flow condition, and it was found that the coefficient of discharge decreases with an increase in clear spacing of rack, slope of bottom rack, specific energy of approach flow, Froude number and Reynolds number. An equation is also being proposed to calculate coefficient of discharge with a maximum error of ± 20%.