A physical model study of the intake structure of the Prairie du Sac Hydroelectric Project was
conducted to assess the distribution of velocities across the intake as an aid in identifying
possible modifications to meet resource agency fish protection criteria. The model was built at a
scale of 1 to 14.
In the model study, approach velocity characteristics were evaluated for a new trash rack placed
upstream of the intake structure replacing the existing trash rack inside the structure. Two
modification scenarios were studied: a trash rack with 1.75-inch openings (68% opening ratio),
and a trash rack with 1.0-inch openings (53% opening ratio).
Flow velocities were measured at 40 locations upstream of the model trash rack, corresponding
to points located approximately one foot upstream of the trash rack in the full-scale (prototype)
structure. Flow velocity measurements were conducted under three flow conditions: 1300 cfs
(representing typical flow through the project’s 3 larger generating units) 1000 cfs (representing
typical flow through the project’s 5 smaller generating units), and 2170 cfs (representing
maximum flow possible through the project’s largest generating unit). Under the 1300 cfs flow
condition, the approach flow velocities did not exceed 1.1 and 1.2 fps with the 1.75- and 1.0-inch
opening trash racks, respectively. The maximum through flow velocities for the 1300 cfs flow
condition were estimated to be 1.9 and 2.4 fps, respectively.
Mohseni, Omid; Leuker, Matthew; Christopher, Richard; Stefan, Heinz G..
Physical Model Study of the Intake Structure of the Prairie Du Sac Hydroelectric Project.
St. Anthony Falls Laboratory.
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