Session

Session 5 2022

Start Date

10-27-2022 12:00 AM

Abstract

A major issue with weirs over erodible beds is the scour downstream, which can seriously challenge their stability. This paper presents experimental results on trapezoidal type-A piano key weirs having two values of bottom slopes keys (28o and 47o). Experiments were conducted in a recirculating channel 10 m long, 0.75 m wide and 0.8 m high. Approach flow depths in the range of 0.032 to 0.07 m, and tailwater depths in the range of 0.08 to 0.18 m were evaluated. It was observed that the bottom slope of weir keys significantly influences the scour depth, such that a 67.8% increase in the slope, increased the average maximum scour depth by about 65%. The maximum scour depth occurred downstream of the outlet keys. Moreover, the scour increased with an increase in the approach flow depth and decreased with the tailwater depth. Distance of location of the maximum scour depth from the weir toe, and length of the scour hole in the weir with key bottom slope of 47o were respectively 5 and 21% greater than the weir with key bottom slope of 28o. In general, the geometric dimensions of the scour hole which were influenced by tailwater depth were more obvious in the model with smaller key bottom slope, such that with a 125% increase in the tailwater depth, the average variations of the scour parameters (maximum scour depth, its distance from the weir toe, and the scour hole length) in the model with smaller key bottom slope were respectively 1.5, 2.5 and 2.7 times those of the other model.

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Oct 27th, 12:00 AM

Local Scour Downstream of Type-A Trapezoidal Piano Key Weir

A major issue with weirs over erodible beds is the scour downstream, which can seriously challenge their stability. This paper presents experimental results on trapezoidal type-A piano key weirs having two values of bottom slopes keys (28o and 47o). Experiments were conducted in a recirculating channel 10 m long, 0.75 m wide and 0.8 m high. Approach flow depths in the range of 0.032 to 0.07 m, and tailwater depths in the range of 0.08 to 0.18 m were evaluated. It was observed that the bottom slope of weir keys significantly influences the scour depth, such that a 67.8% increase in the slope, increased the average maximum scour depth by about 65%. The maximum scour depth occurred downstream of the outlet keys. Moreover, the scour increased with an increase in the approach flow depth and decreased with the tailwater depth. Distance of location of the maximum scour depth from the weir toe, and length of the scour hole in the weir with key bottom slope of 47o were respectively 5 and 21% greater than the weir with key bottom slope of 28o. In general, the geometric dimensions of the scour hole which were influenced by tailwater depth were more obvious in the model with smaller key bottom slope, such that with a 125% increase in the tailwater depth, the average variations of the scour parameters (maximum scour depth, its distance from the weir toe, and the scour hole length) in the model with smaller key bottom slope were respectively 1.5, 2.5 and 2.7 times those of the other model.