Inception Point Relationship for Flat-Sloped Stepped Spillways

Abstract

A two-dimensional, physical model was constructed to evaluate the air entrainment inception point location in a 4(H):1(V) stepped spillway. Step heights of 38, 76, and 152 mm were evaluated. The physical model was constructed with a broad-crested weir, and model unit discharges ranging from 0.11 m3 / ( s⋅m ) to 0.82 m3 / ( s⋅m ) were tested. Hubert Chanson developed a relationship for predicting the inception point location for primarily steep ( θ≥22° ) stepped spillways. In this study, Chanson’s relationship effectively predicts the location of the inception point for slopes as flat as 14° for Froude surface roughness values ( F∗ ) >10 which, in this study, corresponds to model step heights of 38 and 76 mm. A new relationship for predicting the location of the inception point was developed, applicable for flatter sloped ( θ≤22° ) stepped spillways with 1< F∗ <100 . This relationship is similar to Chanson’s, but it is optimized for flat-sloped stepped spillways with a broad-crested weir.