Physical modeling of beveled-face stepped chute

Authors: Hunt, Sherry; Kadavy, Kem; WAHL, TONY - Us Bureau Of Reclamation; MOSES, DANA - Us Army Corp Of Engineers (USACE)

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2022
Publication Date: 1/26/2022
Citation: Hunt, S.L., Kadavy, K.C., Wahl, T.L., Moses, D.W. 2022. Physical modeling of beveled-face stepped chute. Water. 14(3). Article 365. https://doi.org/10.3390/w14030365.
DOI: https://doi.org/10.3390/w14030365

Interpretive Summary: The construction industry has been driven to find a more economical yet aesthetically pleasing method for constructing roller-compacted concrete (RCC) overlays and stepped chutes as a solution for upgrading old earthen dams. Modifying the traditional vertical step face to a 45-degree sloping step face (e.g. beveled) provides both benefits, since slip forms can be used rather than expensive constructed formwork. A physical model study simulating flow over a dam with a 3:1 (Horizontal:Vertical) slope was used to determine the effects of this design change on the hydraulic performance of the stepped chute. Beveled steps moved the start of white-water (aerated flow) about 25 percent upstream compared to traditional vertical steps for the same step height, chute slope, and flow rate. A new equation was developed to predict where white water develops in chutes with 45-degree beveled steps. Above and below the start of the white-water zone, flow depth, average air concentration, and energy losses showed similar trends for vertical and beveled steps. Results are specific to the tested configuration. Additional research is needed to develop general relationships that can be applied to other bevel angles and chute slopes.

Technical Abstract: New construction practices for roller compacted concrete (RCC) overlays and stepped chutes are changing the step geometry from a traditional square-edge, vertical face to a 45 degree beveled face. A large-scale 3(H):1(V) (i.e., q = 18.4 degree) stepped chute model was tested with a 45 degree beveled face step with a height (h) of 152 mm. Results were compared to data on square-edge, vertical face steps previously obtained. The distance to the inception point of free-surface aeration normalized by the surface roughness was reduced approximately 25% for the same Froude number defined in terms of roughness height. An existing inception point relationship for vertical face steps was adjusted with a best fit correction factor to predict the free-surface inception point for this chute slope and beveled face angle. Relative flow depths, mean air concentration, and energy loss data showed similar general trends for vertical face and beveled face steps, but the depths and air concentrations for beveled face steps were slightly higher for equal values of relative free-surface inception point, Li/L, and relative step height (e.g., h/dc). Energy loss at the free-surface inception point ranged from approximately 20 to 40% of total head for both step types. Additional research is needed to determine the generalized effects of the bevel angle and the chute slope on flow properties. This research is expected to be used by field engineers for the design of stepped chutes with beveled face steps.