With the recent and continuing increases in energy consumption, combined with strong environmental concerns, there has been a resurgence in the development of low-impact hydroelectric projects throughout North America and internationally. Within North America, the proposed developments have generally been limited to smaller run-of-river developments or the addition of low-head powerplants to existing in-river structures. Of particular interest have been the hydropower additions adjacent to existing lock and dam structures within the Ohio and Upper Mississippi River Basins. The existing lock and dam facilities are maintained and operated by the U.S. Army Corps of Engineers and were developed to provide safe and efficient navigation along the rivers for commercial transport of goods. With the addition of a hydropower project, the developer is required to demonstrate that there will be no adverse impacts on navigation and flood levels within the vicinity of the project.This paper will consolidate and discuss the results of nine physical model studies that have been conducted for hydropower additions adjacent to existing lock and dam projects. The primary objective for each of the studies was to evaluate and resolve any impacts on navigation that the proposed development might impose. Secondary objectives have included verifying that the project would not adversely impact flood levels, scour and erosion or environmental habitats in the vicinity of the project. In addition, the project designers have utilized the models to refine the alignment and geometry of the powerhouse approach channel to minimize head losses while providing uniform flow distribution entering the powerhouse intake. In each case, the physical modeling was instrumental in optimizing a project layout that minimized the impacts on river navigation while providing approach and tailrace flow conditions compatible with efficient power generation. The experience gained and the “lessons learned” on the various projects are summarized and discussed, and design recommendations are developed that can be applied to future projects
Lock and Dam
The twin cities hydropower project located at the Mississippi Lock and Dam No. 1 (P-362) in St. Paul, MN is seeking to be certified as a low-impact project under the Low Impact Hydropower Institute's (LIHI) certification criteria.
The 17.92 MW project was licensed by FERC in November 2004 and is located within the Mississippi National River and Recreation Area (MNRRA).
According to the application for certification, the project consists of