Simplistic Design Methods for Moderate-Sloped Stepped Chutes: Fid-Bau Portal

Simplistic Design Methods for Moderate-Sloped Stepped Chutes

Hunt, Sherry L. / Kadavy, Kem C. / Hanson, Gregory J.

Numerous research contributions have been made on the hydraulic properties for steep, stepped chutes. Stepped chutes applied to more moderate slopes like those for aging embankment dams are a growing trend, and research activities as a result have increased in this arena. Although numerous stepped chute design guidelines are available, some of them are complicated and somewhat cumbersome to use. A multiyear, large-scale physical model study was conducted for a broad range of step height ( $h$ ) to critical flow depth ( $d_{c}$ ) ratio and chute slope ( $θ$ ) (i.e., ${0.035 \leq h / d}_{c} \leq 2.27$ and $14 ° \leq θ \leq 26.6 °$ ). The objectives of the study were to (1) evaluate the step height to critical flow depth ratio and the chute slope affect on the surface inception point, clear water and bulked flow depth, air concentration, and energy coefficient; and (2) develop practical, straight-forward design relationships for practicing engineers. Detailed flow measurements were collected during testing, and the results were compared in terms of free-surface inception point, air-water flow properties, and energy dissipation. Free-surface inception point relationships were validated for a broader range of use. Relationships for air concentration, clear water flow depth, and energy coefficient were developed, and findings showed these relationships are a function of (1) the length from the downstream edge of the broad-crested weir to the point of interest to the characteristic length from the downstream edge of the broad-crested weir to the free-surface inception point ( ${L / L}_{i}$ ) ratio, (2) the step height to critical flow depth ( ${h / d}_{c}$ ) ratio, and/or (3) the chute slope ( $θ$ ).