Investigation of local scour and discharge characteristics of single step broad crested weirs

Scour control process considered as the main objective to ensure safety and economical design of hydraulic structures to prevent any serious failure in the future. Many types of research showed that local scour downstream of single step broad crested weir decreased five times in comparison with a traditional weir. In this study single step broad crested weir with height (21) cm at downstream and ten models of them are investigated. The first group is four models of ramps with different angles at the downstream of weir and six models of hollow end sill with different heights and porosity. The measurements were tested under three discharges for a duration of 6 hours, and the velocity field was measured by using an Acoustic Doppler Velocimeter. The present results showed that the ramp with an angle (10.80) is the best model to decrease local scour hole volume and a maximum depth of scour. It is also found that the end sill with height (24) cm and porosity (35%) give a low local scour hole volume and maximum depth of scour. The minimum distance of scour from weir is an important issue to prevent failure of weir in the future. In this research, the single broad crested weir was modified to produce minimum local scour at downstream and also reduces costs because there is no need to use countermeasures for reducing the scour depth by lining with rubbles and riprap to protect failure.