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Title: RECOVERING AND ENHANCING STABILITY OF SPILLWAY TO REDEDICATE WHITE OAK DAM

Author
item LIN, S - FERC
item PHILLIPPE, JON - VA DEP CONSEV REC
item CLEMENTS, L - RAPIDAN SERVICE AUTHORITY
item Temple, Darrel

Submitted to: State Dam Safety Officials Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/10/1999
Publication Date: N/A
Citation: Lin, S.S., Phillippe, J., Clements, L.L., Temple, D.M. 1999. Recovering and enhancing stability of spillway to rededicate white oak dam. In: Dam Safety 1999. Proceedings of the Association State Dam Safety Officials., October 1999, St. Louis, MO. 1999 CDROM.

Interpretive Summary: White Oak Dam in Virginia provided flood protection to the downstream flood plain during a major flood in 1995. A flood of the magnitude experienced is unusual and is estimated to have only 0.5 percent chance of occurrence in a given year. As a result of this unusually large flow, the structure's earth auxiliary spillway sustained major erosion damage. Different alternatives for spillway repair were considered, and a decision was made to repair the spillway with roller compacted concrete. The results of the evaluation of alternatives are reported and may assist others faced with the need to make similar evaluations.

Technical Abstract: Earth auxiliary spillways are designed to carry infrequent flood flows around the dam and protect the structure during extreme events. It is anticipated that these spillways may sustain erosion damage during these events. They are considered to have functioned satisfactorily if breach does not occur. The White Oak Dam spillway sustained major damage in 1995 with a flood having a likelihood of occurrence of approximately once every 500 years. The issue of reconditioning or reconstructing this severely damaged spillway is reviewed in this paper. The recently developed SITES computer program was used to verify the original spillway's performance and to evaluate repair alternatives involving replacement of earth fill. The research concerning alternative rehabilitation schemes included structural design, hydraulics, existing geology, available material, site constraints, construction costs and risk-based analysis. The final selection for this dam was the Roller Compacted Concrete (RCC) stepped spillway scheme based on all of the above factors, especially structural integrity, geological harmony, site constraints, hydraulic efficiency, and the results of economic risk analysis. The integrity of the resulting spillway is a major factor in the justification for this method of spillway rehabilitation.