Northern States Power Company (NSP) is examining various alternatives
to modify the automatic spillway gates at the Wissota Hydro Plant on the
Chippewa River at Chippewa Falls, Wisconsin. The gates are called
"stauwerke" gates. The main purpose of the study is to assure that the
automatic spillway gates operate properly during a probable-maximum-flood
(PMF) as required by the Federal Energy Re&ulatory Commission (FERC)
and the Department of Natural Resources (DNR). The position of the gates
must be controllable so that they can be fully lowered or raised with Lake
Wissota at its normal elevation of 898.0 ft. The gates must also be fully
open during a PMF. The spillway has 13 automatic gates each 64 feet wide
in the configuration shown in Fig. 1. Figure 2 shows a photo of the
prototype spillway with gate 1 starting at the south abutment on the right.
Each gate is connected to a 144.5 ton counterweight through linkages and
arms as shown in Fig. 3. Records of openings and closings from 1982 to
1985 show that the gates have operated automatically. Gates 2 through 13
open when the lake elevation is about 0.6 ft above the normal elevation of
898 ft and close when the elevation drops about 0.5 ft below normal. Gate 1
is controlled by a chain hoist and can be pulled down to about 6 ft and used
to somewhat control the lake elevation. When the gates open automatically,
they open a distance of 3.1 to 3.6 feet. The maximum opening of the gates
was 6 feet in the 1941 flood. The 13 gates were expected to be capable of
passing 263,000 cfs. With the PMF of 363,000 cfs, other means have to be
provided to pass the extra 100,000 cfs. Therefore, the questions are whether
or not the gates will operate properly, and if the anticipated flow can be
passed. Presently, in the fully lowered position the gates will be 10 feet
below pool El. 898 ft. By removing curbs around the gate arm openings, the
gates would be horizontal and thus down 10.83 feet. It is not possible to
test the prototype gates in the fully lowered position. Therefore, NSP
proposed to run field tests on Gate 1 of the Wissota Dam spillway, correlate
the results with a physical hydraulic model at the St. Anthony Falls
Hydraulic Laboratory, and expand the model studies to test conditions not
possible in the prototype.
Dahlin, Warren Q.; Wetzel, Joseph M.; Stefan, Heinz G..
Wissota Hydro Plant Automatic Spillway Gate Studies Phase I.
St. Anthony Falls Hydraulic Laboratory.
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