Hydraulic Analysis of the Minnesota Falls Hydroelectric Project

Abstract

The City of Granite Falls, located in southwestern Minnesota, is currently in the process of preparing a FERC License Application for a Minor Water Project at the Minnesota Falls Dam, located on the Minnesota River. The Draft License Application, prepared in February 1997, stated that the proposed Minnesota Falls Hydro Facility would be used to mitigate the peaking effects caused by the Granite Falls Hydro Facility, located 3 miles upstream, such that the flows downstream of Minnesota Falls would equal the inflows to the Granite Falls Hydro Facility. In addition, development of hydropower at the Minnesota Falls site would require directing some of the flow away from the main spillway and through a conduit to the powerhouse. Two major concerns related to river flows were raised during the Initial Consultation stage of licensing: (1) the capability of the Minnesota Falls development to mitigate peaking of the existing Granite Falls facility, and (2) assurance of minimum flows in the riffle section between the Minnesota Falls Dam and the powerhouse tailrace area. The area between the dam and the powerhouse tailrace consists of a natural riffle flow section that is unique in the Minnesota River. While the Minnesota Department of Natural Resources recognized that a net run-of-river system would be a positive step towards improving the aquatic community, they were concerned about potential impacts to the riffle section. Concerns regarding impacts to the riffle habitat resulted in establishing minimum flow requirements. A hydraulic model was prepared to evaluate the ability of the proposed Minnesota Falls operation to mitigate the peaking effects and meet minimum flow requirements in the riffle section. This paper describes the hydraulic model used for the study, the model capabilities, and the results.