Velocity Measurements in Vicinity of a Removable Spillway Weir

Spillways at dams on the Columbia River and main tributaries are of the tainter-gate type, which discharge water beneath the gate structure when open. An experimental overflow weir was installed in one of the Lower Granite Dam (LGD) spillway bays in the Snake River in the Fall of 2001. Called the Removable Spillway Weir, or RSW, its purpose is to take advantage of the surface oriented behavior of migrating juvenile salmonids to provide a more natural entrance for downstream passage. This paper presents the first year of a multiyear study of turbulent flows adjacent to the RSW. The goal of this project is to relate turbulence characteristics in the LGD forebay to fish movement, fish behavior, and hydrodynamic modeling results considering the operation of the RSW. Tasks included in the first year of study include site preparation, stand construction, protocol testing, and velocity collection. Field data characterizing flow paths were collected in the near field of the LGD forebay using an Acoustic Doppler Velocimeter (ADV). Measurements were taken from the face of the RSW using a sampling platform equipped with several motors to allow for a full range of movement. Three dimensional velocity vectors were measured at a sampling rate of 25 Hz. Due to low suspended solids in the water, turbulence parameters could not be defined; only mean velocities were obtained. These and future data will be used to assist in CFD model validation, corroborate fish tracking data, assess juvenile salmonid response to turbulence levels, and to compare field data to natural turbulence levels in natural rivers upstream. Results from this study can be used to improve fish passage technology.