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United States Department of Agriculture

Agricultural Research Service

Title: Physical Model Study of the Proposed Spillway for Cedar Run Site 6, Fauquier County, Virginia (Change Title and Add Accept. Date)

Authors
item Rice, Charles
item Kadavy, Kem

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 5, 1997
Publication Date: N/A

Interpretive Summary: The USDA-NRCS contracted with a consultant to design an emergency spillway and stilling basin for Cedar Run Site 6, Fauquier County, VA. The proposed spillway is a roller compacted concrete spillway with a slope of 0.7H:1V and USBR Type III stilling basin. The USDA-ARS Hydraulic Engineering Research Unit was contracted to conduct a two-dimensional physical model study of the proposed stepped spillway and stilling basin to evaluate the hydraulic performance of the stepped surfaces, effect of entrance abutments, adequacy of the stilling basin, and performance of a flip bucket under different spillway configurations. A smooth chute was also tested to permit comparison of the energy dissipation for the stepped surface and a conventional smooth concrete surface. The steps were effective in dissipating energy; at the design discharge, the energy dissipation with the steps was 32% compared with 7.2% with the smooth surface. We also determined that the stilling basin length can be reduced 20-25% without affecting performance, resulting in considerable dollars saved. The flip bucket appears to be a viable alternative to the use of the stilling basin. Square abutments had greater contraction of the nappe at the entrance compared with rounded abutments. However, considering the difficulty of construction and increased cost for rounded abutments, square abutments are recommended. These findings will permit the consultants to confidently design the structure, and can be used by others in similar situations.

Technical Abstract: A two-dimensional physical model study was conducted of a proposed RCC stepped spillway and stilling basin to evaluate the hydraulic performance of the stepped surfaces, effect of entrance abutments, adequacy of the stilling basin, and performance of a flip bucket. The PMF peak discharge was 27.34 m**3/s/m; the stilling basin design discharge 18.31 m**3/s/m. A smooth chute was also tested to permit comparison of the energy dissipatio for the stepped surface and a conventional smooth concrete surface. The steps were effective in dissipating energy. At the stilling basin design discharge, the energy dissipation with the steps was 32% compared with 7.2% with the smooth surface. The stilling basin was very effective in dissipating energy at 18.31 m**3/s/m and smaller discharges and can be reduced 20-25 percent in length without negatively affecting performance. The flip bucket appears to be a viable alternative to the use of the stilling basin. Square abutments had greater contraction of the nappe at the entrance compared with rounded abutments. However, considering the difficulty of construction and increased cost for rounded abutments, square abutments are recommended.

Last Modified: 7/22/2014
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