Hydraulic computations for stepped concrete overlays of embankment dams

Authors: WAHL, TONY - Us Bureau Of Reclamation; Hunt, Sherry; Kadavy, Kem; FALVEY, HENRY - Henry T Falvey & Associates, Inc

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/20/2022
Publication Date: N/A
Citation: N/A

Interpretive Summary: Flood control dams originally built in rural areas to protect farmland are increasingly being counted on to protect new urban developments. To do so, they must meet greater requirements for safe operation during large floods. Many earthen dams are now being modified with concrete overlays that protect the dam from erosion when large floods pass over the dam. Roller compacted concrete is an economical construction material that uses no reinforcing steel and can be placed quickly with earth-moving equipment. A side benefit is obtained because the material is placed in horizontal layers so that a stair-stepped surface is naturally produced on the downstream slope. The resulting steps absorb flow energy so that the downstream channel can also be more easily protected against erosion.

Technical Abstract: One method for rehabilitating and modernizing embankment dams is the addition of a concrete overlay that allows floods to be passed over the dam and protects the embankment from erosion. Roller compacted concrete is commonly used, which makes it practical to use a stepped construction that also enhances energy dissipation. Analysis of flow conditions over such structures requires computation of aerated flow and its effects on flow depth, training wall design, and energy dissipation. This paper describes the use of SpillwayPro, an energy-based water surface profile calculation tool for smooth spillway chutes (Wahl et al. 2019), recently improved to also analyze stepped chutes. The tool is applicable to a wide range of chute slopes, including flatter slopes typical of embankment dam overlays and steeper slopes encountered on concrete gravity dams. The use of an energy-based analysis allows SpillwayPro to be applied to some situations differing from the idealized configurations covered by empirical relations (Hunt & Kadavy 2013; Hunt et al. 2014), such as non-constant slopes, varying step heights, and converging chutes. SpillwayPro integrates water surface profile calculations, aerated flow effects, and cavitation analysis, which is potentially important for steeper slopes and large unit discharges. Simultaneous calculation of smooth and stepped-chute flow profiles enables rapid assessment of the energy dissipation benefits of steps, as well as a comparison of the aerated flow and cavitation issues for smooth vs. stepped chute constructions.