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Research Project: Development of Engineering Tools for the Design and Rehabilitation of Safe, Efficient Embankment Protection Alternatives, Hydraulic Structures, and Channels

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Title: Stilling basin design for stepped chutes: More than one type to consider

Author
item Hunt, Sherry
item Kadavy, Kem

Submitted to: State Dam Safety Officials Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/1/2017
Publication Date: 9/12/2017
Citation: Hunt, S., Kadavy, K.C. 2017. Stilling basin design for stepped chutes: More than one type to consider. In: Dam Safety 2017. Proc. of the Assoc. of State Dam Safety Officials Annual Conf., 09/10-15/17, San Antonio, TX, 2 p.

Interpretive Summary:

Technical Abstract: Scientists with the USBR developed stilling basin design criteria for smooth chute spillways. Advances in concrete technology has allowed for the economical design of stepped chutes for maximizing energy dissipation and potentially allowing for a shorter stilling basin footprint as compared to one for a smooth chute. Modifications to the chute surface forces designers to consider the hydraulic performance of stilling basins when highly aerated flow enters the basin. Design parameters for stilling basin include Froude number, clear water flow depth, and sequent flow depth. Type I, type II, type III, and type IV stilling basins for stepped chutes are being evaluated at the USDA-ARS Hydraulic Engineering Research Unit in Stillwater, OK. The evaluation includes the collection of pressures within the basin, water surface elevations, photography, and videography. Findings indicate Froude numbers based on the entering clear water flow depth for stilling basins designed for stepped chutes on slopes between 10 and 30 degrees can range from 3.3 less than or equal to F less than or equal to 5.5. Hydraulic jumps created in the stilling basin when transitioning from stepped chutes are visually observed to oscillate for Froude numbers less than approximately 4.5. The oscillations and the resulting waves propagating downstream were observed to be dampened and minimized by energy dissipation blocks or a dentated sill, but were not significantly improved by increasing the tailwater level above the recommended value for each type of basin. This research is intended to provide practicing engineers guidance on designing stilling basins for stepped chutes.