Initial Appraisal Report -- May 1998

Screening Document -- October 1998

Plan of Study for Chief Joseph Dam Gas Abatement -- April 1999

System Study -- Initiated January 1999

• Plan of Study
• Overview

Near-Field Study -- Conducted June 1999

• Plan of Study
• Study Report

Physical Model Studies -- in progress

General Reevaluation Report -- May 2000

Final Environmental Assessment and Finding of No Significant Impact

• Dissolved Gas Abatement Final EA/FONSI

The sectional model was watered up for the first time in September 1999. Viewing of the model without flow deflectors revealed that the nappe of the flow at Chief Joseph Dam is thinner than at the lower river dams with flow deflectors probably due to its higher head (180 feet) and steeper slope.

In October 1999, several agency representatives visited WES to view and discuss modeling and analysis. The agencies represented were Colville Confederated Tribes, Washington State Department of Ecology, NMFS, and BPA. The NMFS participant submitted a trip report.

As of 6 January 2000, three deflectors have been examined and performance curves for each have been developed. The three deflectors have the same 10-foot radius of curvature and the same elevation of 776 fmsl, but differ in length: 8, 12.5, and 17 feet. They were each examined at a variety of flows and tailwater elevations. The results were used to create a performance curve for each length. From the performance curve, it can be seen that the 12.5-foot deflector had the largest range of skimming flows, a desired outcome. All three deflectors produced about the same range for the combined skimming and undulating flows. From these results, it was determined that 12.5 feet was the best of the three. The next step was to overlay tailwater frequency data on top of the performance curves to optimize deflector elevation. The result was a 12.5-foot deflector at elevation 779 fmsl.

The next step for analysis will be to determine, with the 12.5-foot deflector, how high the flow would need to be for the nappe to override the lip of the deflector. The deflector should be short enough so that the energy of flows greater than the normal high flow condition is dissipated in the stilling basin. In other words, high flows continue to plunge as the spillway was originally designed. Otherwise, the high energy has the potential to erode the channel downstream of the stilling basin. Once the result of this effort is available, we will determine the following steps in the physical model studies.

Performance curves

PDF files with photos of each deflector under various spill and tailwater conditions

8 feet long, 2000 cfs per spillbay
8 feet long, 4270 cfs per spillbay
8 feet long, 6630 cfs per spillbay
8 feet long, 9030 cfs per spillbay
8 feet long, 11360 cfs per spillbay

12.5 feet long, 2000 cfs per spillbay
12.5 feet long, 4270 cfs per spillbay
12.5 feet long, 6630 cfs per spillbay
12.5 feet long, 9030 cfs per spillbay
12.5 feet long, 11360 cfs per spillbay

17 feet long, 2000 cfs per spillbay
17 feet long, 4270 cfs per spillbay
17 feet long, 6630 cfs per spillbay
17 feet long, 9030 cfs per spillbay
17 feet long, 11360 cfs per spillbay

Spreadsheets with Data

8-foot deflector
12.5-foot deflector
17-foot deflector

Calibration of the general model powerhouse and spillway has just been completed. In addition, downstream channel velocities in the general model match those collected during the near-field study in June 1999, providing verification not always possible in a general model. Once a final design is determined from the sectional model, it will be placed in the general model where 3-dimensional flow conditions will be examined, including velocity, bed movement/scour, rightbank implications, and possible entrainment of material into the stilling basin.

A few samples of the kinds of general model testing photos are below. More will be available as general model flow deflector testing begins.

For more information on the Chief Joseph Dam Dissolved Gas Abatement Study, please contact the Seattle District Corps of Engineers:

Marian Valentine, Hydraulic Engineer, (206) 764-3543
marian.l.valentine@usace.army.mil

Mike Deering, Hydraulic Engineer, (206) 764-3595
michael.k.deering@usace.army.mil

Beth Coffey, Project Manager, (206) 764-4478
frances.e.coffey@usace.army.mil