History of Bee Tree Dam and Spillway and a Preview for the Wednesday Field Trip to Bee Tree Dam

Abstract Only - Bee Tree Dam is located on Bee Tree Creek, a tributary of the Swannanoa River, in Buncombe County, North Carolina. The dam, owned by the City of Asheville, is part of the water supply system for the City of Asheville, Buncombe and Henderson Counties in North Carolina.
The embankment dam, constructed in 1925, is a semi-hydraulic fill structure with a height of approximately 177 feet. The dam was designed by Charles Waddell and he supervised the construction, maintaining strict control of the hydraulic sluicing of the core materials, as reported in the Engineering News Record. The original spillway was located on the rock abutment at the right end of the embankment dam. The spillway structure consisted of an ungated concrete ogee weir section, approximately 100 feet in length that converges into a concrete-lined chute outlet channel 30 feet in width. The intake tower is a concrete structure located in the reservoir. The tower, which is approximately 125 feet high, contains a vertical cast iron pipe 30 inches in diameter with fifteen 16-inch inlet valves. A gallery tunnel, 539-feet in length extends from the intake tower through rock and then through the left side of the embankment to the downstream side of the dam. The tunnel/conduit houses the raw waterline and mudline pipes.
The dam is classified as a Very Large, High-Hazard dam under the criteria of the North Carolina 1967 Dam Safety Law. The original spillway was significantly undersized, passing approximately the 1/3 probable maximum precipitation (PMP) storm event without overtopping. The required design storm for this dam was determined during the 1980’s by the NC State Dam Safety Office to be the ¾ PMP storm event.
The dam was repaired, including total spillway replacement, in 2001-2002. To accommodate the required design storm, the spillway was replaced by a new spillway that is 180 feet wide at the ogee weir, with sidewalls that converge to a 60-foot wide chute section. Model studies were conducted at the St. Anthony Falls Hydraulics Laboratory, St. Paul, MN, to confirm the required chute width for alternative combinations of weir widths and the unsymmetrical sidewall convergence angles. In addition, the top of dam was raised with a 7-foot high reinforced concrete parapet along the top of the existing dam. The new spillway ogee weir is divided into two levels (a 100-foot wide low level and an 80-foot wide high level) so that the 100-year storm discharge will not be increased in the new spillway, as the downstream valley is heavily populated.