Bird Haven Dam
Bird Haven Dam is owned, maintained, and operated by the Lord Fairfax Soil and Water Conservation District (District). The District has an easement on the land, which is owned by Bird Haven Lake LLC. Dam is one of 104 dams owned by Soil and Water Conservation Districts in Virginia. A few homes border the lake, and the lake and the surrounding area provide ground water recharge and a haven for wildlife. This earthen flood control dam was completed in 1972 at a cost of $297,721. It is 70 feet high by 601 feet long. The normal water surface elevation (the Normal Pool) is just below the top of the concrete riser located in the lake. The area of the Normal Pool is 16 acres and that of the watershed is 2,965 acres.
The dam was originally designed to store all the water that would run off the watershed in a 100-year, 24-hour storm (6.5 inches in 24 hours). This water would be slowly released through the principal spillway in the concrete riser. The large grassy area at the side of the dam was the emergency, or auxiliary, spillway. When a storm event produces more runoff than can be stored by the dam, the excess water flows through the emergency spillway rather than overtopping the dam.
The District operates the dam under an operating certificate from the Virginia Soil and Water Conservation Board. A professional engineer from the Department of Conservation and Recreation (DCR), Division of Dam Safety and Flood Plain Management works with District personnel to identify and address all maintenance concerns. Similarly, the District is subject to regulation and oversight by the federal Natural Resources Conservation Service (NRCS), which also provides technical advice and assistance to the District. Since the District has no funds for major repairs, problem analysis, or improvements, it has looked in the past to DCR for the necessary financial support.
In Virginia dams are classified in three categories: high hazard; moderate hazard; and low hazard. The area that would be under water in the event of a dam failure is called the Inundation Zone. Dams that have people living in the Inundation Zone are classified as high hazard dams. The Bird Haven Dam has always been a high hazard dam. Engineering studies in 2009 and 2010 resulted in maps that show the area of downstream flooding under various scenarios. There are approximately 200 homes, businesses or other buildings in the Inundation Zone; and there could be an estimated 1,400 people at risk, along with potential infrastructure disruption to utilities, 17 roads and an airport. At the time it was built, the dam met all safety standards. The District maintains a current Emergency Action Plan (EAP) that goes into operation if there is a risk of flooding or other problems at the dam. In cooperation with the State and Shenandoah County Emergency Services, the EAP is revised annually and regular drills and exercises are conducted to ensure that the plan is current.
Since September 2008, Virginia’s Impounding Structures Regulation has required that high hazard dams safely convey a Probable Maximum Flood (PMF). The PMF is defined as a flooding event resulting from a Probable Maximum Precipitation (PMP) event. The PMP is the theoretically greatest amount of precipitation for a given duration (6, 12, or 24-hour periods must be analyzed in accordance with Virginia’s impounding regulations) that is meteorologically possible over a given size storm area at a particular geographic location. In such an event, there would have been 26 to 38 inches of rain, and thus there would be extensive flooding both above and below the dam, but the dam itself should be designed so it would not fail. Though professionals differ on the precise number, one engineer calculated that Bird Haven Dam would withstand .73 PMF. Consequently, the District initiated discussions with both the federal and State governments to obtain improvement funds.
Funding for this rehabilitation came from a bond issue authorized by the Virginia legislature. Bird Haven dam was among the first five on the list for improvement. DCR Design and Construction (DAC) selected Schnabel Dam Engineering, Inc., as the architect/engineer (A/E) for the project. Schnabel completed the first stage of this project, in which alternatives were prepared for the “footprint” of the improvements. A public meeting was held in February 2012 at which representatives of Schnabel and DAC explained the alternatives and answered questions. The best alternative was chosen and Schnabel completed the design documents for the improvements to the dam. The design included a concrete emergency spillway to replace the original earthen spillway. A hard copy of the design documents can be reviewed at the District office. A final public informational meeting was held on September 24, 2013.
A Request for Proposals, to complete construction of the improvements at both Bird Haven and Lake Laura dams, was advertised in March of 2015. A prebid meeting was held on site and four prequalified bidders attended and the scope of the project was reviewed. Sealed bids from all four contracting firms were received and opened on April 2, 2015. After review of the bids, ASI Contractors was award a construction contract to complete the work at both Bird Haven and Lake Laura dams. Construction began in August 2015 and was completed by the Fall of 2016.
Lord Fairfax Soil and Water Conservation District
VA DCR, Division of Dam Safety and Flood Plain Management
Bird Haven Lake LLC