Rehabilitation on high-hazard 3.3-MW Brainerd hydroelectric facility dam apron raises concerns

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Concern with regard to repair of the dam’s concrete spillway apron was raised in a public forum at the Brainerd Public Utilities (BPU) Commission meeting held Jan. 27.

In June 2014, the City of Brainerd, Minn., and its Public Utilities Commission, purchased the 3.342-MW Brainerd hydroelectric project, originally constructed in the late 1880s in central Minnesota on the Mississippi River, for US$2.6 million. Prior to the city’s purchase, guidelines set by the Federal Energy Regulatory Commission (FERC) and applied by the Minnesota Department of Natural Resources (MDNR) determined the facility has a high-hazard dam.

The Brainerd Dispatch reports a worker who retired from the company contracted to repair the dam’s spillway apron attempted to “raise concerns” about the dam’s safety. But, the worker was stopped while speaking after he displayed an unauthorized image of the facility’s spillway apron infrastructure.

The Dispatch indicates Larry Prahm, who reportedly retired in good standing from the company on Dec. 1, 2014, addressed the commission regarding his concern that the dam could fail when water from spring rains enter the facility because its spillway apron is not being properly repaired. To support his position, Prahm produced what he said was a copy of a recent x-ray of the spillway’s apron. He was not authorized to have the image or release it publically, and BPU Commission President Lucy Nesheim prevented Prahm from making further comments.

In general terms, a concrete apron is the area of concrete constructed on the reservoir floor that leads to the impoundment side of a dam, extending beyond the dam wall, downstream. The apron prevents water from washing out the dam’s foundation, and among its several attributes, an apron’s thickness, width and length are site-specific.

In its February 2014 Legislative Report issued to state and federal Minnesota representatives and the City of Brainerd, MDNR said, “The dam is classified as a high-hazard dam because failure of the dam during a flood event may result in the loss of life and significant property damage downstream.”

The report also said, “The most urgent repair need is the reconstruction of the concrete spillway apron scheduled for 2014. This project entails removing deteriorated concrete and constructing new reinforced concrete features in the downstream side of the dam to dissipate the energy of the water going over the spillway. This estimated US$1.5 million project is required by FERC and will be the responsibility of Brainerd Public Utilities.”

Brainerd is a major tourist area in the central part of the state that, according to 2010 census data, has about 92,000 inhabitants in nearby areas downstream from the dam.

Brainerd Dam is a 25-foot-high concrete, L-shaped dam that has a 2,500-acre impoundment and a powerhouse containing five generating units. Its former owner, Wausau Paper Mills, used energy generated from the facility until it closed the mill in 2013.
 

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