Project: Little Goose 1:40-scale Sectional Model
PI: Steve Wilhelms
Branch/Group: Inland Hydraulic Structures Branch, Environmental Hydraulics Group
Project Description/Activities/Capabilities:
The purpose of the Little Goose 1:40-scale section model was to define operational
characteristics of the existing deflector and stilling basin and alternative deflector designs; define
performance characteristics of a divider wall to separate powerhouse discharge from spillway
discharge; and verify the minimum spillway flow and tailwater elevation associated with debris
movement.
Sponsor: Walla Walla District. POC Sean Milligan.
Personnel: Steve Wilhelms, TEM Murphy, Laurin Yates, Calvin Buie
Project Location and Description:
Little Goose Dam is located on the Snake River at river mile 70.3. The powerhouse at Little
Goose Dam consists of 6 hydroturbines with a combined capacity of over 120 kcfs and the
spillway has a total width of 512 feet and consists of 8 radial gate-controlled bays 50 ft in width.
8-ft-long flow deflectors, with no transition radius, have been installed on spill bays 2 through 6 at
elevation 532 ft. The flip bucket stilling basin is shorter (80 ft) and deeper (invert elevation 466.5
ft) than the horizontal apron-type stilling basins used at the other Snake River projects. The
maximum depth of flow in the stilling basin is typically over 70 ft deep during normal tailwater
conditions. A training wall extending over 100 ft from the north end of the powerhouse, separates
the south side of the stilling basin from the powerhouse. A rock groin extends perpendicular to
the dam at the north adult fish entrance. The tailwater channel below the powerhouse narrows
quickly due to the presence of a peninsula containing fish passage facilities. The lock outlet is
located about 500 ft downstream from the powerhouse on the south bank. The elevation of the
tailwater channel downstream of the stilling basin ranges from 450 to 480 ft. A steep shelf 20-30
feet high extends across the tailwater channel 100 ft downstream of the stilling basin. The
tailwater channel gradually becomes shallower downstream of the shelf ranging in elevation from
500 to 520 ft. The thalweg of the Snake River channel runs along the north bank of tailwater
channel below the earthen embankment section of Little Goose Dam. The channel narrows
considerably within one-mile of the dam resulting in a channel width of about 1350 ft at the
location of the fixed monitoring station.
Facilities: Bldg. 5016
Related Topic Areas: Physical models, flow deflectors, dissolved gas, entrainment flow, debris
movement, rivers, reservoirs, hydraulic structures, fish passage, surface water, hydropower