RFB-104-19 DOW – Bullock Pen Lake Dam Rehabilitation
RFB-104-19 DOW – Bullock Pen Lake Dam Rehabilitation
Project Manager Name: Frank Phillips
Phone: (502) 782-0331
Email:
frank.phillips@ky.gov
Estimate:
$11,955,906.00
Estimated Length of Project:
766 (Substantial Completion) + 30 (Final Completion)
Bullock Pen Lake Dam is an earthen dam with a crest elevation that varies from elevation 768.1 feet near the left abutment to elevation 766.4 feet at the principal spillway at the right end of the dam. The dam crest is approximately 670 feet long with an average crest width of about 10 feet. The upstream and downstream slopes of the embankment are 3H:1V and 2.5H:1V, respectively. The maximum section of the dam has a height of approximately 50 feet. The centerline of the dam has an east-west alignment that extends from Rainbow Drive at the left abutment to within about 250 feet of Gun Club Road at the right abutment. The downstream face of the dam faces south toward Lebanon Road.
The existing spillway is an excavated rock channel with a 115-foot wide concrete control section. The dam also has a low-level drain pipe consisting of a 16-inch diameter cast iron bell and spigot pipe with an upstream invert at elevation 720.8 feet (according to historic drawings) and a downstream invert at elevation 719.8 feet. An existing control valve is located at the downstream end of the pipe. The location of the inlet/upstream end of the pipe in the reservoir is unknown.
The dam is classified as a Class C high hazard structure. The design storm for a Class C high hazard structure is the Probable Maximum Precipitation (PMP); however, the existing spillway can only pass approximately 24% of the PMP without overtopping the dam. In addition, within a few years after construction and shortly after initial filling of the reservoir, erosion of the shale in the excavated rock spillway channel in the right abutment was observed, and that erosion continues to progress.
The proposed modifications to the Bullock Pen Lake Dam include the construction of a 12½-cycle, 260-foot wide reinforced concrete labyrinth spillway with a stepped chute over the dam embankment. The proposed spillway is sized to safely pass flows from storm events up to the PMP. Modifications also include raising the crest of the dam to elevation 770.3 feet, providing internal embankment drain and filter systems, re-grading the upstream and downstream slopes of the existing embankment to match the existing slope angles of 3H:1V and 2.5H:1V, respectively, addressing historic seepage issues in the existing spillway, and closure of the existing spillway and spillway outlet channel. In addition to these modifications, the existing low-level drain pipe will be filled with grout and abandoned. A siphon, consisting of a 24-inch diameter high-density polyethylene (HDPE) pipe, will be installed at the left end of the proposed spillway and will serve as the new low-level drain. Miscellaneous site improvements, such as drainage improvements and the construction of permanent site access roads, are also proposed.
A temporary stream diversion and work protection system will also be constructed by the Contractor to allow the lake to be maintained near its normal pool elevation and to provide a minimum 25-year level of protection to the work during construction. A staged steel sheet pile and sand bag cofferdam system will be constructed in the existing embankment upstream of the work area, and flows will be diverted through the existing spillway or new labyrinth spillway depending on the stage of construction. The cofferdam system has been designed by the Engineer; however, the design of additional temporary stream diversion works, and the construction, maintenance, and safe removal of all temporary works will be the responsibility of the Contractor. The Contractor will be required to submit a Control of Water Plan detailing their approach, calculations (where applicable), and proposed sequencing for the temporary stream diversion works.
Project Location: Boone and Grant