Project: Lower Granite Total Dissolved Gas Exchange Study
PI: Mike Schneider
Project Description/Activities/Capabilities:
The purpose of this field study was to define and quantify processes that contribute to dissolved
gas transfer during spill at Lower Granite Dam. In general, the transfer of dissolved gas has been
found to be a function of the unit spillway discharge, spill pattern, spillway geometry, stilling basin
and tailwater depth and flow conditions, forebay TDG concentration, project head, and water
temperature. This study focused on resolving questions regarding the change in TDG saturation
in the Snake River cause by project operations at Lower Granite Dam.
Sponsor: Walla Walla District, POC Lynn Reese
Personnel: Mike Schneider
Project Location and Description:
Lower Granite Lock and Dam is the upstream-most project on the Lower Snake
River, located 107.5 miles above the Snake River confluence with the Columbia
River. The main structure includes the powerhouse, spillway and stilling basin,
navigation lock, fish facilities, concrete non-overflow sections, and a rock-filled
embankment adjacent to the north shore. The dam spans 3,200 ft including the
earthen non-overflow embankment. The powerhouse is located near the south shore
with the spillway and navigation lock to the north. The powerhouse consists of six
generator bays with a maximum total discharge capacity of 130,000-cfs. The
powerhouse capacity is only 123 kcfs when all units are operated within 1 percent of
peak efficiency. The turbine units are numbered from 1 to 6 starting at the south
bank. The Lower Granite spillway is 512 ft long. It has eight 50-ft-wide spillway
bays separated by seven 14-f-wide piers. The spill bays are numbered consecutively
form north to south. The spillway crest elevation is 681.0 fmsl. The spillway
discharge is controlled by eight radial (tainter) gates that are 50 ft wide by 60 ft
high. The spillway will pass the project design flood of 850,000-cfs, with the
maximum pool elevation of 746.5 fmsl, and the standard project flow of 678,000-cfs
with the normal full pool elevation 738.0 fmsl. A raised spillway crest was added to
spillbay 1 during the winter of 2002. The RSW is operated in a full open or closed
mode with an average discharge of about 6.8 kcfs.
Facilities: Field Study
Related Topic Areas: Hydrualic Structures, Environmental Studies, Spillway Flow Deflectors,
Total Dissolved Gas, Hydropower, reservoir
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